Re: Missing errcode() in ereport
Hi, On 2020-03-30 11:54:03 +0800, Craig Ringer wrote: > On Fri, 20 Mar 2020, 01:59 Andres Freund, wrote: > > On 2020-03-17 10:09:18 -0400, Tom Lane wrote: > > > We might want to spend some effort thinking how to find or prevent > > > additional bugs of the same ilk ... > > > > Yea, that'd be good. Trying to help people new to postgres write their > > first patches I found that ereport is very confusing to them - largely > > because the syntax doesn't make much sense. Made worse by the compiler > > error messages being terrible in many cases. > > > Very much agreed. > > I'd have found it helpful to just have the docs explain clearly how it > works by chaining the comma operator using functions with ignored return > values. IDK, that seems like it'll be a bit too implementation specific. > That would also help people understand how they can make parts of an > ereport conditional, e.g. only set errdetail() if there additional info is > currently available W/O duplicating the rest of the ereport . Well, they can do whatever they can in any function argument list. I don't see why the ereport docs are a good place to explain ... ? ... : ... ? Or am I misunderstanding what you suggest here? > Not sure there's much we can do without changing ereport's "signature" I think the changes we just did already improved the situation a good bit. Both by obviating the need for the additional parentheses, as well as making parameters outside of err*() trigger warnings, and also generally better error/warning messages. I still think we might want to do a bigger change of the logging APIs. See the messages leading up to https://postgr.es/m/20190805214952.dmnn2oetdquixpp4%40alap3.anarazel.de and the message linked from there. Greetings, Andres Freund
Re: Missing errcode() in ereport
Craig Ringer writes: > I'd have found it helpful to just have the docs explain clearly how it > works by chaining the comma operator using functions with ignored return > values. Want to write some text? > That would also help people understand how they can make parts of an > ereport conditional, e.g. only set errdetail() if there additional info is > currently available W/O duplicating the rest of the ereport . There are examples of that in the tree, of course, but maybe an example in the docs wouldn't be bad either. regards, tom lane
Re: Missing errcode() in ereport
On Fri, 20 Mar 2020, 01:59 Andres Freund, wrote: > Hi, > > On 2020-03-17 10:09:18 -0400, Tom Lane wrote: > > We might want to spend some effort thinking how to find or prevent > > additional bugs of the same ilk ... > > Yea, that'd be good. Trying to help people new to postgres write their > first patches I found that ereport is very confusing to them - largely > because the syntax doesn't make much sense. Made worse by the compiler > error messages being terrible in many cases. Very much agreed. I'd have found it helpful to just have the docs explain clearly how it works by chaining the comma operator using functions with ignored return values. That would also help people understand how they can make parts of an ereport conditional, e.g. only set errdetail() if there additional info is currently available W/O duplicating the rest of the ereport . Not sure there's much we can do without changing ereport's "signature" > though :( > > Regards, > > Andres > > >
Re: Missing errcode() in ereport
I wrote:
> Thomas Munro writes:
>> I think this caused anole to say:
>> "reloptions.c", line 1362: error #2042: operand types are incompatible
>> ("void" and "int")
>> errdetail_internal("%s", _(optenum->detailmsg)) : 0));
> Yeah, I was just looking at that :-(
> We could revert the change to have these functions return void,
> or we could run around and change the places with this usage
> pattern to use "(void) 0" instead of just "0". The latter would
> be somewhat painful if only minority compilers warn, though.
> Also, I don't think that having to change ereport usage was part
> of the agreed-to plan here ... so I'm leaning to the former.
Done that way.
regards, tom lane
Re: Missing errcode() in ereport
Thomas Munro writes:
> I think this caused anole to say:
> "reloptions.c", line 1362: error #2042: operand types are incompatible
> ("void" and "int")
> errdetail_internal("%s", _(optenum->detailmsg)) : 0));
Yeah, I was just looking at that :-(
We could revert the change to have these functions return void,
or we could run around and change the places with this usage
pattern to use "(void) 0" instead of just "0". The latter would
be somewhat painful if only minority compilers warn, though.
Also, I don't think that having to change ereport usage was part
of the agreed-to plan here ... so I'm leaning to the former.
regards, tom lane
Re: Missing errcode() in ereport
On Wed, Mar 25, 2020 at 9:30 AM Tom Lane wrote:
> Andres Freund writes:
> > On 2020-03-23 17:24:49 -0400, Tom Lane wrote:
> >> Hearing no objections, I started to review Andres' patchset with
> >> that plan in mind.
>
> > Thanks for pushing the first part!
>
> I pushed all of it, actually.
I think this caused anole to say:
"reloptions.c", line 1362: error #2042: operand types are incompatible
("void" and "int")
errdetail_internal("%s", _(optenum->detailmsg)) : 0));
Re: Missing errcode() in ereport
Andres Freund writes: > On 2020-03-23 17:24:49 -0400, Tom Lane wrote: >> Hearing no objections, I started to review Andres' patchset with >> that plan in mind. > Thanks for pushing the first part! I pushed all of it, actually. regards, tom lane
Re: Missing errcode() in ereport
On 2020-03-23 17:24:49 -0400, Tom Lane wrote: > Hearing no objections, I started to review Andres' patchset with > that plan in mind. Thanks for pushing the first part!
Re: Missing errcode() in ereport
Andres Freund writes:
> I wondered before whether there's a way we could move the elevel check
> in errstart to the macro. For it to be a win we'd presumably have to
> have a "synthesized" log_level variable, basically
> min(log_min_messages, client_min_messages, ERROR).
> Probably not worth it.
Yeah, I don't really agree with that idea. The whole business of which
elevels will trigger output is fundamentally policy, not mechanism,
and you do not want policy decisions embedded into ABI so that there
are hundreds of copies of them. It's a loss for code size and a worse
loss if you ever want to change the behavior.
> On 2020-03-23 17:24:49 -0400, Tom Lane wrote:
>> One thing I'm not totally sure about is whether we can rely on
>> this change:
>>
>> -extern void errfinish(int dummy,...);
>> +extern void errfinish(void);
>>
>> being fully ABI-transparent. One would think that as long as errfinish
>> doesn't inspect its argument(s) it doesn't matter whether any are passed,
>> but maybe somewhere there's an architecture where the possible presence
>> of varargs arguments makes for a significant difference in the calling
>> convention? We could leave that change out of the v12 patch if we're
>> worried about it.
> I would vote for leaving that out of the v12 patch. I'm less worried
> about odd architectures, and more about sanitizers and/or compilers
> emitting "security enhanced" code checking signatures match etc
> ("control flow integrity").
Yeah, good point. Let's skinny the v12 patch down to just macro
and docs changes, then, not touching elog.c at all.
I made a commitfest entry for this just to see what the cfbot
thinks of it, but if there are not objections we should go ahead
and push in a day or so, IMO.
regards, tom lane
BTW, the CF app is showing me as the first author, even though
I definitely put you in first. Guess it doesn't care about
author ordering ... is that a bug to be fixed?
Re: Missing errcode() in ereport
Hi,
On 2020-03-23 17:24:49 -0400, Tom Lane wrote:
> I wrote:
> > On balance I'm leaning towards keeping the parens as preferred style
> > for now, adjusting v12 so that the macro will allow paren omission
> > but we don't break ABI, and not touching the older branches.
>
> Hearing no objections, I started to review Andres' patchset with
> that plan in mind. I noted two things that I don't agree with:
>
> 1. I think we should write the ereport macro as
>
> if (errstart(...)) \
> __VA_ARGS__, errfinish(...); \
>
> as I had it, not
>
> if (errstart(...)) \
> { \
> __VA_ARGS__; \
> errfinish(...); \
> } \
>
> as per Andres. The reason is that I don't have as much faith in the
> latter construct producing warnings for no-op expressions.
Hm. I don't think it'll be better, but I don't have a problem going with
yours either.
> 2. We cannot postpone the passing of the "domain" argument as Andres'
> 0003 patch proposes, because that has to be available to the auxiliary
> error functions so they do message translation properly.
Ah, good point.
I wondered before whether there's a way we could move the elevel check
in errstart to the macro. For it to be a win we'd presumably have to
have a "synthesized" log_level variable, basically
min(log_min_messages, client_min_messages, ERROR).
Probably not worth it.
> Maybe it'd be possible to finagle things to postpone translation to
> the very end, but the provisions for errcontext messages being
> translated in a different domain would make that pretty ticklish.
> Frankly I don't think it'd be worth the complication. There is a
> clear benefit in delaying the passing of filename (since we can skip
> that strchr() call) but beyond that it seems pretty marginal.
Fair enough.
> Other than that it looks pretty good. I wrote some documentation
> adjustments and re-split the patch into 0001, which is proposed for
> back-patch into v12, and 0002 which would have to be HEAD only.
Cool.
> One thing I'm not totally sure about is whether we can rely on
> this change:
>
> -extern void errfinish(int dummy,...);
> +extern void errfinish(void);
>
> being fully ABI-transparent. One would think that as long as errfinish
> doesn't inspect its argument(s) it doesn't matter whether any are passed,
> but maybe somewhere there's an architecture where the possible presence
> of varargs arguments makes for a significant difference in the calling
> convention? We could leave that change out of the v12 patch if we're
> worried about it.
I would vote for leaving that out of the v12 patch. I'm less worried
about odd architectures, and more about sanitizers and/or compilers
emitting "security enhanced" code checking signatures match etc
("control flow integrity").
Greetings,
Andres Freund
Re: Missing errcode() in ereport
I wrote:
> On balance I'm leaning towards keeping the parens as preferred style
> for now, adjusting v12 so that the macro will allow paren omission
> but we don't break ABI, and not touching the older branches.
Hearing no objections, I started to review Andres' patchset with
that plan in mind. I noted two things that I don't agree with:
1. I think we should write the ereport macro as
if (errstart(...)) \
__VA_ARGS__, errfinish(...); \
as I had it, not
if (errstart(...)) \
{ \
__VA_ARGS__; \
errfinish(...); \
} \
as per Andres. The reason is that I don't have as much faith in the
latter construct producing warnings for no-op expressions.
2. We cannot postpone the passing of the "domain" argument as Andres'
0003 patch proposes, because that has to be available to the auxiliary
error functions so they do message translation properly. Maybe it'd
be possible to finagle things to postpone translation to the very end,
but the provisions for errcontext messages being translated in a different
domain would make that pretty ticklish. Frankly I don't think it'd be
worth the complication. There is a clear benefit in delaying the passing
of filename (since we can skip that strchr() call) but beyond that it
seems pretty marginal.
Other than that it looks pretty good. I wrote some documentation
adjustments and re-split the patch into 0001, which is proposed for
back-patch into v12, and 0002 which would have to be HEAD only.
One thing I'm not totally sure about is whether we can rely on
this change:
-extern void errfinish(int dummy,...);
+extern void errfinish(void);
being fully ABI-transparent. One would think that as long as errfinish
doesn't inspect its argument(s) it doesn't matter whether any are passed,
but maybe somewhere there's an architecture where the possible presence
of varargs arguments makes for a significant difference in the calling
convention? We could leave that change out of the v12 patch if we're
worried about it.
regards, tom lane
diff --git a/doc/src/sgml/sources.sgml b/doc/src/sgml/sources.sgml
index 32ca220..283c3e0 100644
--- a/doc/src/sgml/sources.sgml
+++ b/doc/src/sgml/sources.sgml
@@ -103,9 +103,9 @@ less -x4
message text. In addition there are optional elements, the most
common of which is an error identifier code that follows the SQL spec's
SQLSTATE conventions.
-ereport itself is just a shell function, that exists
+ereport itself is just a shell macro, that exists
mainly for the syntactic convenience of making message generation
-look like a function call in the C source code. The only parameter
+look like a single function call in the C source code. The only parameter
accepted directly by ereport is the severity level.
The primary message text and any optional message elements are
generated by calling auxiliary functions, such as errmsg,
@@ -116,36 +116,50 @@ less -x4
A typical call to ereport might look like this:
ereport(ERROR,
-(errcode(ERRCODE_DIVISION_BY_ZERO),
- errmsg("division by zero")));
+errcode(ERRCODE_DIVISION_BY_ZERO),
+errmsg("division by zero"));
This specifies error severity level ERROR (a run-of-the-mill
error). The errcode call specifies the SQLSTATE error code
using a macro defined in src/include/utils/errcodes.h. The
-errmsg call provides the primary message text. Notice the
-extra set of parentheses surrounding the auxiliary function calls
-these are annoying but syntactically necessary.
+errmsg call provides the primary message text.
+
+
+
+You will also frequently see this older style, with an extra set of
+parentheses surrounding the auxiliary function calls:
+
+ereport(ERROR,
+(errcode(ERRCODE_DIVISION_BY_ZERO),
+ errmsg("division by zero")));
+
+The extra parentheses were required
+before PostgreSQL version 12, but are now
+optional.
Here is a more complex example:
ereport(ERROR,
-(errcode(ERRCODE_AMBIGUOUS_FUNCTION),
- errmsg("function %s is not unique",
-func_signature_string(funcname, nargs,
- NIL, actual_arg_types)),
- errhint("Unable to choose a best candidate function. "
- "You might need to add explicit typecasts.")));
+errcode(ERRCODE_AMBIGUOUS_FUNCTION),
+errmsg("function %s is not unique",
+ func_signature_string(funcname, nargs,
+ NIL, actual_arg_types)),
+errhint("Unable to choose a best candidate function. "
+"You might need to add explicit typecasts."));
This illustrates the use of format codes to embed run-time values into
a message text. Also, an optional hint message is provided.
+The auxiliary function calls can be written in any order, but
+
Re: Missing errcode() in ereport
On 2020-Mar-19, Tom Lane wrote: > I think the key decision we'd have to make to move forward on this > is to decide whether it's still project style to prefer the extra > parens, or whether we want new code to do without them going > forward. If we don't want to risk requiring __VA_ARGS__ for the > old branches then I'd vote in favor of keeping the parens as > preferred style, at least till v11 is out of support. If we do > change that in the back branches then there'd be reason to prefer > to go without parens. New coders might still be confused about > why there are all these calls with the useless parens, though. It seems fine to accept new code in pg14 without the extra parens. All existing committers are (or should be) used to the style with the parens, so it's unlikely that we'll mess up when backpatching bugfixes; and even if we do, the buildfarm would alert us to that soon enough. -- Álvaro Herrerahttps://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: Missing errcode() in ereport
Andres Freund writes: > On 2020-03-19 22:32:30 -0400, Tom Lane wrote: >> Could we get away with moving the compiler goalposts for the back >> branches? I dunno, but it's a fact that we aren't testing anymore >> with any compilers that would complain about unconditional use of >> __VA_ARGS__. So it might be broken already and we wouldn't know it. > FWIW, I did grep for unprotected uses, and didn't find anything. Yeah, I also grepped the v11 branch for that. >> (I suspect the last buildfarm animal that would've complained about >> this was pademelon, which I retired more than a year ago IIRC.) > I guess a query that searches the logs backwards for animals without > __VA_ARGS__ would be a good idea? I did a more wide-ranging scan, looking at the 9.4 branch as far back as 2015. Indeed, pademelon is the only animal that ever reported not having __VA_ARGS__ in that timeframe. So I've got mixed emotions about this. On the one hand, it seems quite unlikely that anyone would ever object if we started requiring __VA_ARGS__ in the back branches. On the other hand, it's definitely not project policy to change requirements like that in minor releases. Also the actual benefit might not be much. If anyone did mistakenly back-patch a fix that included a paren-free ereport, the buildfarm would point out the error soon enough. I thought for a little bit about making the back branches define ereport with "..." if HAVE__VA_ARGS and otherwise not, but if we did that then the buildfarm would *not* complain about paren-free ereports in the back branches. I think that would inevitably lead to there soon being some, so that we'd effectively be requiring __VA_ARGS__ anyway. (I suppose I could resurrect pademelon ... but who knows whether that old war horse will keep working for another four years till v11 is retired.) On balance I'm leaning towards keeping the parens as preferred style for now, adjusting v12 so that the macro will allow paren omission but we don't break ABI, and not touching the older branches. But if there's a consensus to require __VA_ARGS__ in the back branches, I won't stand in the way. regards, tom lane
Re: Missing errcode() in ereport
Hi, On 2020-03-19 22:32:30 -0400, Tom Lane wrote: > Andres Freund writes: > > I wonder if it'd become a relevant backpatch pain if we started to have > > some ereports() without the additional parens in 13+. > > Yeah, it would be a nasty backpatch hazard. > > > Would it perhaps > > make sense to backpatch just the part that removes the need for the > > parents, but not the return type changes? > > I was just looking into that. It would be pretty painless to do it > in v12, but before that we weren't requiring C99. Having said that, > trolling the buildfarm database shows exactly zero active members > that don't report having __VA_ARGS__, in the branches where we test > that. (And pg_config.h.win32 was assuming that MSVC had that, too.) > > Could we get away with moving the compiler goalposts for the back > branches? I dunno, but it's a fact that we aren't testing anymore > with any compilers that would complain about unconditional use of > __VA_ARGS__. So it might be broken already and we wouldn't know it. FWIW, I did grep for unprotected uses, and didn't find anything. > (I suspect the last buildfarm animal that would've complained about > this was pademelon, which I retired more than a year ago IIRC.) I guess a query that searches the logs backwards for animals without __VA_ARGS__ would be a good idea? > > We can also remove elog() support code now, because with __VA_ARGS__ > > support it's really just a wrapper for ereport(elevel, > > errmsg(__VA_ARGS_)). This is patch 0002. > > Yeah, something similar had occurred to me but I didn't write the patch > yet. Note it should be errmsg_internal(); Oh, right. > also, does the default for errcode come out the same? I think so - there's no distinct code setting sqlerrcode in elog_start/finish. That already relied on errstart(). > > I wonder if its worth additionally ensuring that errcode, errmsg, > > ... are only called within errstart/errfinish? > > Meh. That's wrong at least for errcontext(), and I'm not sure it's > really worth anything to enforce it for the others. Yea, I'm not convinced either. Especially after changing the err* return types to void, as that presumably will cause errors with a lot of incorrect parens, e.g. about a function with void return type as an argument to errmsg(). > I think the key decision we'd have to make to move forward on this > is to decide whether it's still project style to prefer the extra > parens, or whether we want new code to do without them going > forward. If we don't want to risk requiring __VA_ARGS__ for the > old branches then I'd vote in favor of keeping the parens as > preferred style, at least till v11 is out of support. Agreed. > If we do change that in the back branches then there'd be reason to > prefer to go without parens. New coders might still be confused about > why there are all these calls with the useless parens, though. That seems to be an acceptable pain, from my POV. Greetings, Andres Freund
Re: Missing errcode() in ereport
Andres Freund writes: > I wonder if it'd become a relevant backpatch pain if we started to have > some ereports() without the additional parens in 13+. Yeah, it would be a nasty backpatch hazard. > Would it perhaps > make sense to backpatch just the part that removes the need for the > parents, but not the return type changes? I was just looking into that. It would be pretty painless to do it in v12, but before that we weren't requiring C99. Having said that, trolling the buildfarm database shows exactly zero active members that don't report having __VA_ARGS__, in the branches where we test that. (And pg_config.h.win32 was assuming that MSVC had that, too.) Could we get away with moving the compiler goalposts for the back branches? I dunno, but it's a fact that we aren't testing anymore with any compilers that would complain about unconditional use of __VA_ARGS__. So it might be broken already and we wouldn't know it. (I suspect the last buildfarm animal that would've complained about this was pademelon, which I retired more than a year ago IIRC.) > We can also remove elog() support code now, because with __VA_ARGS__ > support it's really just a wrapper for ereport(elevel, > errmsg(__VA_ARGS_)). This is patch 0002. Yeah, something similar had occurred to me but I didn't write the patch yet. Note it should be errmsg_internal(); also, does the default for errcode come out the same? > I think it might also be a good idea to move __FILE__, __LINE__, > PG_FUNCNAME_MACRO, domain from being parameters to errstart to > errfinish. For elevel < ERROR its sad that we currently pass them even > if we don't emit the message. This is patch 0003. Oh, that's a good idea that hadn't occurred to me. > I wonder if its worth additionally ensuring that errcode, errmsg, > ... are only called within errstart/errfinish? Meh. That's wrong at least for errcontext(), and I'm not sure it's really worth anything to enforce it for the others. I think the key decision we'd have to make to move forward on this is to decide whether it's still project style to prefer the extra parens, or whether we want new code to do without them going forward. If we don't want to risk requiring __VA_ARGS__ for the old branches then I'd vote in favor of keeping the parens as preferred style, at least till v11 is out of support. If we do change that in the back branches then there'd be reason to prefer to go without parens. New coders might still be confused about why there are all these calls with the useless parens, though. regards, tom lane
Re: Missing errcode() in ereport
Hi, On 2020-03-19 21:03:17 -0400, Tom Lane wrote: > I wrote: > > I think that at least some compilers will complain about side-effect-free > > subexpressions of a comma expression. Could we restructure things so > > that the errcode/errmsg/etc calls form a standalone comma expression > > rather than appearing to be arguments of a varargs function? > > Yeah, the attached quick-hack patch seems to work really well for > this. Heh, you're too fast. I just sent something similar, and a few followup patches. What is your thinking about pain around backpatching it might introduce? We can't easily backpatch support for ereport-without-extra-parens, I think, because it needs __VA_ARGS__? > As a nice side benefit, the backend gets a couple KB smaller from > removal of errfinish's useless dummy argument. I don't think it's the removal of the dummy parameter itself that constitutes most of the savings, but instead it's not having to push the return value of errmsg(), errcode(), et al as vararg arguments. > I think that we could now also change all the helper functions > (errmsg et al) to return void instead of a dummy value, but that > would make the patch a lot longer and probably not move the > goalposts much in terms of error detection. I did include that in my prototype patch. Agree that it's not necessary for the error detection capability, but it seems misleading to leave the return values around if they're not actually needed. > It also looks like we could use the same trick to get plain elog() > to have the behavior of not evaluating its arguments when it's > not going to print anything. I've not poked at that yet either. I've included a patch for that. I think it's now sufficient to #define elog(elevel, ...) \ ereport(elevel, errmsg(__VA_ARGS__)) which imo is quite nice, as it allows us to get rid of a lot of duplication. Greetings, Andres Freund
Re: Missing errcode() in ereport
Hi, On 2020-03-19 19:32:55 -0400, Tom Lane wrote: > Andres Freund writes: > > On 2020-03-19 14:07:04 -0400, Tom Lane wrote: > >> Now that we can rely on having varargs macros, I think we could > >> stop requiring the extra level of parentheses, > > > I think that'd be an improvement, because: > > ane of the ones I saw confuse people is just: > > /home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: error: > > ‘ereport’ undeclared (first use in this function); did you mean ‘rresvport’? > > 3727 |ereport(FATAL, > > |^~~ > > |rresvport > > /home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: note: each > > undeclared identifier is reported only once for each function it appears in > > because the extra parens haven't been added. > > Ah, so the macro isn't expanded at all if it appears to have more than > two parameters? That seems odd, but I suppose some compilers might > work that way. Switching to varargs would improve that for sure. Yea. Newer gcc versions do warn about a parameter mismatch count, which helps. I'm not sure what the preprocessor / compiler should do intead? FWIW, clang also doesn't expand the macro. > > Another one I've both seen and committed byself is converting an elog to > > an ereport, and not adding an errcode() around the error code - which > > silently looks like it works. > > You mean not adding errmsg() around the error string? Yeah, I can > believe that one easily. It's sort of the same problem as forgetting > to wrap errcode() around the ERRCODE_ constant. Both of these, I think. > Could we restructure things so that the errcode/errmsg/etc calls form > a standalone comma expression rather than appearing to be arguments of > a varargs function? The compiler's got no hope of realizing there's > anything wrong when it thinks it's passing an integer or string > constant to a function it knows nothing about. But if it could see > that nothing at all is being done with the constant, maybe we'd get > somewhere. Worth a try. Not doing a pointless varargs call could also end up reducing elog overhead a bit (right now we push a lot of 0 as vararg arguments for no reason). A quick hack suggests that it works: /home/andres/src/postgresql/src/backend/tcop/postgres.c: In function ‘process_postgres_switches’: /home/andres/src/postgresql/src/backend/tcop/postgres.c:3728:27: warning: left-hand operand of comma expression has no effect [-Wunused-value] 3728 | (ERRCODE_SYNTAX_ERROR, | ^ /home/andres/src/postgresql/src/include/utils/elog.h:126:4: note: in definition of macro ‘ereport_domain’ 126 |rest; \ |^~~~ /home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: note: in expansion of macro ‘ereport’ 3727 |ereport(FATAL, |^~~ and in an optimized build the resulting code indeed looks a bit better: before: textdata bss dec hex filename 8462795 176128 204464 8843387 86f07b src/backend/postgres Looking at FloatExceptionHandler as an example: 2860/* We're not returning, so no need to save errno */ 2861ereport(ERROR, 0x00458bc0 <+0>: push %rbp 0x00458bc1 <+1>: mov$0xb2d,%edx 0x00458bc6 <+6>: lea0x214c9b(%rip),%rsi# 0x66d868 0x00458bcd <+13>:mov%rsp,%rbp 0x00458bd0 <+16>:push %r13 0x00458bd2 <+18>:xor%r8d,%r8d 0x00458bd5 <+21>:lea0x2d9dc4(%rip),%rcx# 0x7329a0 <__func__.41598> 0x00458bdc <+28>:push %r12 0x00458bde <+30>:mov$0x14,%edi 0x00458be3 <+35>:callq 0x5a8c00 0x00458be8 <+40>:lea0x214e59(%rip),%rdi# 0x66da48 0x00458bef <+47>:xor%eax,%eax 0x00458bf1 <+49>:callq 0x5acb00 0x00458bf6 <+54>:mov%eax,%r13d 0x00458bf9 <+57>:lea0x1bf7fb(%rip),%rdi# 0x6183fb 0x00458c00 <+64>:xor%eax,%eax 0x00458c02 <+66>:callq 0x5ac710 0x00458c07 <+71>:mov$0x1020082,%edi 0x00458c0c <+76>:mov%eax,%r12d 0x00458c0f <+79>:callq 0x5ac5b0 0x00458c14 <+84>:mov%eax,%edi 0x00458c16 <+86>:mov%r13d,%edx 0x00458c19 <+89>:mov%r12d,%esi 0x00458c1c <+92>:xor%eax,%eax 0x00458c1e <+94>:callq 0x5ac020 vs after: textdata bss dec hex filename 8395731 176128 204464 8776323 85ea83 src/backend/postgres 2861ereport(ERROR, 0x00449dd0 <+0>: push %rbp 0x00449dd1 <+1>: xor%r8d,%r8d 0x00449dd4 <+4>: lea0x2d8a65(%rip),%rcx# 0x722840 <__func__.41598> 0x00449ddb <+11>:mov%rsp,%rbp 0x00449dde <+14>:mov$0xb2d,%edx 0x00449de3
Re: Missing errcode() in ereport
I wrote:
> I think that at least some compilers will complain about side-effect-free
> subexpressions of a comma expression. Could we restructure things so
> that the errcode/errmsg/etc calls form a standalone comma expression
> rather than appearing to be arguments of a varargs function?
Yeah, the attached quick-hack patch seems to work really well for this.
I find that this now works:
ereport(ERROR,
errcode(ERRCODE_DIVISION_BY_ZERO),
errmsg("foo"));
where before it gave the weird error you quoted. Also, these both
draw warnings about side-effect-free expressions:
ereport(ERROR,
ERRCODE_DIVISION_BY_ZERO,
errmsg("foo"));
ereport(ERROR,
"%d", 42);
With gcc you just need -Wall to get such warnings, and clang
seems to give them by default.
As a nice side benefit, the backend gets a couple KB smaller from
removal of errfinish's useless dummy argument.
I think that we could now also change all the helper functions
(errmsg et al) to return void instead of a dummy value, but that
would make the patch a lot longer and probably not move the
goalposts much in terms of error detection.
It also looks like we could use the same trick to get plain elog()
to have the behavior of not evaluating its arguments when it's
not going to print anything. I've not poked at that yet either.
regards, tom lane
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 62eef7b..a29ccd9 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -438,7 +438,7 @@ matches_backtrace_functions(const char *funcname)
* See elog.h for the error level definitions.
*/
void
-errfinish(int dummy,...)
+errfinish(void)
{
ErrorData *edata = [errordata_stack_depth];
int elevel;
@@ -1463,7 +1463,7 @@ elog_finish(int elevel, const char *fmt,...)
/*
* And let errfinish() finish up.
*/
- errfinish(0);
+ errfinish();
}
@@ -1749,7 +1749,7 @@ ThrowErrorData(ErrorData *edata)
recursion_depth--;
/* Process the error. */
- errfinish(0);
+ errfinish();
}
/*
@@ -1863,7 +1863,7 @@ pg_re_throw(void)
*/
error_context_stack = NULL;
- errfinish(0);
+ errfinish();
}
/* Doesn't return ... */
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 0a4ef02..e6fa85f 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -118,34 +118,34 @@
*--
*/
#ifdef HAVE__BUILTIN_CONSTANT_P
-#define ereport_domain(elevel, domain, rest) \
+#define ereport_domain(elevel, domain, ...) \
do { \
pg_prevent_errno_in_scope(); \
if (errstart(elevel, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
- errfinish rest; \
+ __VA_ARGS__, errfinish(); \
if (__builtin_constant_p(elevel) && (elevel) >= ERROR) \
pg_unreachable(); \
} while(0)
#else /* !HAVE__BUILTIN_CONSTANT_P */
-#define ereport_domain(elevel, domain, rest) \
+#define ereport_domain(elevel, domain, ...) \
do { \
const int elevel_ = (elevel); \
pg_prevent_errno_in_scope(); \
if (errstart(elevel_, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
- errfinish rest; \
+ __VA_ARGS__, errfinish(); \
if (elevel_ >= ERROR) \
pg_unreachable(); \
} while(0)
#endif /* HAVE__BUILTIN_CONSTANT_P */
-#define ereport(elevel, rest) \
- ereport_domain(elevel, TEXTDOMAIN, rest)
+#define ereport(elevel, ...) \
+ ereport_domain(elevel, TEXTDOMAIN, __VA_ARGS__)
#define TEXTDOMAIN NULL
extern bool errstart(int elevel, const char *filename, int lineno,
const char *funcname, const char *domain);
-extern void errfinish(int dummy,...);
+extern void errfinish(void);
extern int errcode(int sqlerrcode);
Re: Missing errcode() in ereport
Andres Freund writes: > On 2020-03-19 14:07:04 -0400, Tom Lane wrote: >> Now that we can rely on having varargs macros, I think we could >> stop requiring the extra level of parentheses, > I think that'd be an improvement, because: > ane of the ones I saw confuse people is just: > /home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: error: > ‘ereport’ undeclared (first use in this function); did you mean ‘rresvport’? > 3727 |ereport(FATAL, > |^~~ > |rresvport > /home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: note: each > undeclared identifier is reported only once for each function it appears in > because the extra parens haven't been added. Ah, so the macro isn't expanded at all if it appears to have more than two parameters? That seems odd, but I suppose some compilers might work that way. Switching to varargs would improve that for sure. > Another one I've both seen and committed byself is converting an elog to > an ereport, and not adding an errcode() around the error code - which > silently looks like it works. You mean not adding errmsg() around the error string? Yeah, I can believe that one easily. It's sort of the same problem as forgetting to wrap errcode() around the ERRCODE_ constant. I think that at least some compilers will complain about side-effect-free subexpressions of a comma expression. Could we restructure things so that the errcode/errmsg/etc calls form a standalone comma expression rather than appearing to be arguments of a varargs function? The compiler's got no hope of realizing there's anything wrong when it thinks it's passing an integer or string constant to a function it knows nothing about. But if it could see that nothing at all is being done with the constant, maybe we'd get somewhere. regards, tom lane
Re: Missing errcode() in ereport
Hi,
On 2020-03-19 14:07:04 -0400, Tom Lane wrote:
> Andres Freund writes:
> > On 2020-03-17 10:09:18 -0400, Tom Lane wrote:
> >> We might want to spend some effort thinking how to find or prevent
> >> additional bugs of the same ilk ...
>
> > Yea, that'd be good. Trying to help people new to postgres write their
> > first patches I found that ereport is very confusing to them - largely
> > because the syntax doesn't make much sense. Made worse by the compiler
> > error messages being terrible in many cases.
>
> > Not sure there's much we can do without changing ereport's "signature"
> > though :(
>
> Now that we can rely on having varargs macros, I think we could
> stop requiring the extra level of parentheses, ie instead of
>
> ereport(ERROR,
> (errcode(ERRCODE_DIVISION_BY_ZERO),
> errmsg("division by zero")));
>
> it could be just
>
> ereport(ERROR,
> errcode(ERRCODE_DIVISION_BY_ZERO),
> errmsg("division by zero"));
>
> (The old syntax had better still work, of course. I'm not advocating
> running around and changing existing calls.)
I think that'd be an improvement, because:
> I'm not sure that this'd really move the goalposts much in terms of making
> it any less confusing, but possibly it would improve the compiler errors?
> Do you have any concrete examples of crummy error messages?
ane of the ones I saw confuse people is just:
/home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: error:
‘ereport’ undeclared (first use in this function); did you mean ‘rresvport’?
3727 |ereport(FATAL,
|^~~
|rresvport
/home/andres/src/postgresql/src/backend/tcop/postgres.c:3727:4: note: each
undeclared identifier is reported only once for each function it appears in
because the extra parens haven't been added.
I personally actually hit a variant of that on a semi-regular basis:
Closing the parens for "rest" early, as there's just so many parens in
ereports, especially if an errmsg argument is a function call
itself. Which leads to a variation of the above error message. I know
how to address it, obviously, but I do find it somewhat annoying to deal
with.
Another one I've both seen and committed byself is converting an elog to
an ereport, and not adding an errcode() around the error code - which
silently looks like it works.
Greetings,
Andres Freund
Re: Missing errcode() in ereport
Andres Freund writes:
> On 2020-03-17 10:09:18 -0400, Tom Lane wrote:
>> We might want to spend some effort thinking how to find or prevent
>> additional bugs of the same ilk ...
> Yea, that'd be good. Trying to help people new to postgres write their
> first patches I found that ereport is very confusing to them - largely
> because the syntax doesn't make much sense. Made worse by the compiler
> error messages being terrible in many cases.
> Not sure there's much we can do without changing ereport's "signature"
> though :(
Now that we can rely on having varargs macros, I think we could
stop requiring the extra level of parentheses, ie instead of
ereport(ERROR,
(errcode(ERRCODE_DIVISION_BY_ZERO),
errmsg("division by zero")));
it could be just
ereport(ERROR,
errcode(ERRCODE_DIVISION_BY_ZERO),
errmsg("division by zero"));
(The old syntax had better still work, of course. I'm not advocating
running around and changing existing calls.)
I'm not sure that this'd really move the goalposts much in terms of making
it any less confusing, but possibly it would improve the compiler errors?
Do you have any concrete examples of crummy error messages?
regards, tom lane
Re: Missing errcode() in ereport
Hi, On 2020-03-17 10:09:18 -0400, Tom Lane wrote: > We might want to spend some effort thinking how to find or prevent > additional bugs of the same ilk ... Yea, that'd be good. Trying to help people new to postgres write their first patches I found that ereport is very confusing to them - largely because the syntax doesn't make much sense. Made worse by the compiler error messages being terrible in many cases. Not sure there's much we can do without changing ereport's "signature" though :( Regards, Andres
Re: Missing errcode() in ereport
On Wed, 18 Mar 2020 at 13:57, Amit Kapila wrote: > > On Wed, Mar 18, 2020 at 9:01 AM Amit Kapila wrote: > > > > On Tue, Mar 17, 2020 at 7:39 PM Tom Lane wrote: > > > > > > Amit Kapila writes: > > > > On Tue, Mar 17, 2020 at 3:28 PM Michael Paquier > > > > wrote: > > > >> Definitely an oversight. All stable branches down to 9.5 have > > > >> mistakes in the same area, with nothing extra by grepping around. > > > >> Amit, I guess that you will take care of it? > > > > > > > Yes, I will unless I see any objections in a day or so. > > > > > > No need to wait, it's a pretty obvious thinko. > > > > > > > Okay, I will push in some time. > > > > Pushed. Thank you! Regards, -- Masahiko Sawadahttp://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: Missing errcode() in ereport
On Wed, Mar 18, 2020 at 9:01 AM Amit Kapila wrote: > > On Tue, Mar 17, 2020 at 7:39 PM Tom Lane wrote: > > > > Amit Kapila writes: > > > On Tue, Mar 17, 2020 at 3:28 PM Michael Paquier > > > wrote: > > >> Definitely an oversight. All stable branches down to 9.5 have > > >> mistakes in the same area, with nothing extra by grepping around. > > >> Amit, I guess that you will take care of it? > > > > > Yes, I will unless I see any objections in a day or so. > > > > No need to wait, it's a pretty obvious thinko. > > > > Okay, I will push in some time. > Pushed. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
Re: Missing errcode() in ereport
On Tue, Mar 17, 2020 at 7:39 PM Tom Lane wrote: > > Amit Kapila writes: > > On Tue, Mar 17, 2020 at 3:28 PM Michael Paquier wrote: > >> Definitely an oversight. All stable branches down to 9.5 have > >> mistakes in the same area, with nothing extra by grepping around. > >> Amit, I guess that you will take care of it? > > > Yes, I will unless I see any objections in a day or so. > > No need to wait, it's a pretty obvious thinko. > Okay, I will push in some time. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
Re: Missing errcode() in ereport
Amit Kapila writes: > On Tue, Mar 17, 2020 at 3:28 PM Michael Paquier wrote: >> Definitely an oversight. All stable branches down to 9.5 have >> mistakes in the same area, with nothing extra by grepping around. >> Amit, I guess that you will take care of it? > Yes, I will unless I see any objections in a day or so. No need to wait, it's a pretty obvious thinko. We might want to spend some effort thinking how to find or prevent additional bugs of the same ilk ... but correcting the ones already found needn't wait on that. regards, tom lane
Re: Missing errcode() in ereport
On Tue, Mar 17, 2020 at 3:28 PM Michael Paquier wrote: > > On Tue, Mar 17, 2020 at 10:26:57AM +0100, Julien Rouhaud wrote: > > On Tue, Mar 17, 2020 at 10:00 AM Amit Kapila > > wrote: > >> +1. This looks like an oversight to me. > > > > good catch! And patch LGTM. > > Definitely an oversight. All stable branches down to 9.5 have > mistakes in the same area, with nothing extra by grepping around. > Amit, I guess that you will take care of it? > Yes, I will unless I see any objections in a day or so. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
Re: Missing errcode() in ereport
On Tue, Mar 17, 2020 at 10:26:57AM +0100, Julien Rouhaud wrote: > On Tue, Mar 17, 2020 at 10:00 AM Amit Kapila wrote: >> +1. This looks like an oversight to me. > > good catch! And patch LGTM. Definitely an oversight. All stable branches down to 9.5 have mistakes in the same area, with nothing extra by grepping around. Amit, I guess that you will take care of it? -- Michael signature.asc Description: PGP signature
Re: Missing errcode() in ereport
On Tue, Mar 17, 2020 at 10:00 AM Amit Kapila wrote:
>
> On Tue, Mar 17, 2020 at 2:08 PM Masahiko Sawada
> wrote:
> >
> > Hi,
> >
> > In PageIsVerified() we report a WARNING as follows:
> >
> > ereport(WARNING,
> > (ERRCODE_DATA_CORRUPTED,
> > errmsg("page verification failed, calculated checksum
> > %u but expected %u",
> > checksum, p->pd_checksum)));
> >
> > However the error message won't have sql error code due to missing
> > errcode(). As far as I can see there are four places:
> >
> > $ git grep "(ERRCODE" | grep -v errcode
> > contrib/adminpack/adminpack.c:
> > (ERRCODE_DUPLICATE_FILE,
> > contrib/adminpack/adminpack.c:
> > (ERRCODE_DUPLICATE_FILE,
> > contrib/adminpack/adminpack.c:
> > (ERRCODE_UNDEFINED_FILE,
> > src/backend/storage/page/bufpage.c:
> > (ERRCODE_DATA_CORRUPTED,
> > src/pl/plpgsql/src/pl_exec.c: else if
> > (ERRCODE_IS_CATEGORY(sqlerrstate) &&
> >
> > Attached patch add errcode() to these places.
> >
>
> +1. This looks like an oversight to me.
good catch! And patch LGTM.
Re: Missing errcode() in ereport
On Tue, Mar 17, 2020 at 2:08 PM Masahiko Sawada
wrote:
>
> Hi,
>
> In PageIsVerified() we report a WARNING as follows:
>
> ereport(WARNING,
> (ERRCODE_DATA_CORRUPTED,
> errmsg("page verification failed, calculated checksum
> %u but expected %u",
> checksum, p->pd_checksum)));
>
> However the error message won't have sql error code due to missing
> errcode(). As far as I can see there are four places:
>
> $ git grep "(ERRCODE" | grep -v errcode
> contrib/adminpack/adminpack.c:
> (ERRCODE_DUPLICATE_FILE,
> contrib/adminpack/adminpack.c:
> (ERRCODE_DUPLICATE_FILE,
> contrib/adminpack/adminpack.c:
> (ERRCODE_UNDEFINED_FILE,
> src/backend/storage/page/bufpage.c:
> (ERRCODE_DATA_CORRUPTED,
> src/pl/plpgsql/src/pl_exec.c: else if
> (ERRCODE_IS_CATEGORY(sqlerrstate) &&
>
> Attached patch add errcode() to these places.
>
+1. This looks like an oversight to me.
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
Missing errcode() in ereport
Hi,
In PageIsVerified() we report a WARNING as follows:
ereport(WARNING,
(ERRCODE_DATA_CORRUPTED,
errmsg("page verification failed, calculated checksum
%u but expected %u",
checksum, p->pd_checksum)));
However the error message won't have sql error code due to missing
errcode(). As far as I can see there are four places:
$ git grep "(ERRCODE" | grep -v errcode
contrib/adminpack/adminpack.c:
(ERRCODE_DUPLICATE_FILE,
contrib/adminpack/adminpack.c: (ERRCODE_DUPLICATE_FILE,
contrib/adminpack/adminpack.c:
(ERRCODE_UNDEFINED_FILE,
src/backend/storage/page/bufpage.c:
(ERRCODE_DATA_CORRUPTED,
src/pl/plpgsql/src/pl_exec.c: else if
(ERRCODE_IS_CATEGORY(sqlerrstate) &&
Attached patch add errcode() to these places.
Regards,
--
Masahiko Sawadahttp://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
add_errcode.patch
Description: Binary data
