[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[doko at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #12 from Matthias Klose  ---
fyi, this is now fixed in Ubuntu 16.04 LTS

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[aivchenk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

Alexander Ivchenko  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |FIXED

--- Comment #11 from Alexander Ivchenko  ---
Fixed with r240057

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[aivchenk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #10 from Alexander Ivchenko  ---
Matthias, could you apply the fix for that bug
(https://gcc.gnu.org/viewcvs?rev=240057=gcc=rev) to the Ubuntu
version of gcc?

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[aivchenk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #9 from Alexander Ivchenko  ---
Looks like exactly the same discussion happened when '-z bndplt' option was
discussed. Here is the reference: https://patchwork.ozlabs.org/patch/456557/ .
It's a long one, but seems that the consensus was formulated by Jeff Law:

"I guess the one thing I don't like here is that whether or not to pass 
-z bndplt is made at the time we configure GCC.  Yet, it's trivial for 
someone to change the system linker later, either to gold or from an old 
BFD linker that doesn't support -z bndplt to one that does support -z 
bndplt.

[ Note we have the same issue with certain assembler feature tests. ]

I'm not aware of any real infrastructure in GCC to query the behavior of 
the linker at link time and then customize the options passed.  So if 
it's going to be configurable, then that's the only time to do the test."
...
"So, in an ideal world, we'd query the linker at link time and pass the 
flag anytime we have a linker that supports the capability and perhaps 
warn if the linker doesn't support that capability.

Given we're not in that ideal world, I think Ilya's patch is reasonable 
and should be installed."

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[aivchenk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #8 from Alexander Ivchenko  ---
Thanks, Matthias, that's a valid point about changing linker on a runtime. In
my defense, I see that right now MPX does not work with '-fuse-ld=bfd' anyways:

>gcc test.c -fcheck-pointer-bounds -mmpx -fuse-ld=gold
/usr/bin/ld.gold: bndplt: unknown -z option
/usr/bin/ld.gold: use the --help option for usage information

That's not a surprise, because the check for '--push-state' is done exactly
like the check for '-z bndplt'.

Would it be possible to probe the 'other' linker (the one that is not the
default one) during a configure time? If so we may end up with something like
HAVE_BFD_PUSHPOPSTATE_SUPPORT/HAVE_GOLD_PUSHPOPSTATE_SUPPORT

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[doko at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #7 from Matthias Klose  ---
yes, you are right about the old linker versions, I forgot about these cases.
But it doesn't help the case when you enable the push/pop for a bfd default
linker, and the fail with gold.

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #6 from Ilya Enkovich  ---
(In reply to Matthias Klose from comment #5)
> I think it's wrong to have HAVE_LD_PUSHPOPSTATE_SUPPORT baked into the
> driver while it can be easily changed with -fuse-ld=bfd.  It would be very
> nice to have these push/pop options implemented in gold as well and avoid
> this kind of work arounds.

Should we really not allow gold for MPX?  Also having this feature in gold
wouldn't allow us to get rid of this macro because users may use old linker
versions.

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[doko at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

Matthias Klose  changed:

   What|Removed |Added

 CC||doko at gcc dot gnu.org

--- Comment #5 from Matthias Klose  ---
I think it's wrong to have HAVE_LD_PUSHPOPSTATE_SUPPORT baked into the driver
while it can be easily changed with -fuse-ld=bfd.  It would be very nice to
have these push/pop options implemented in gold as well and avoid this kind of
work arounds.

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[hjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

--- Comment #4 from hjl at gcc dot gnu.org  ---
Author: hjl
Date: Fri Sep  9 21:38:06 2016
New Revision: 240057

URL: https://gcc.gnu.org/viewcvs?rev=240057=gcc=rev
Log:
Fix PR target/77267

2016-09-10  Alexander Ivchenko  

PR target/77267
* config.in: Regenerate.
* config/i386/linux-common.h (MPX_LD_AS_NEEDED_GUARD_PUSH):
New macro.
(MPX_LD_AS_NEEDED_GUARD_PUSH): Ditto.
(LIBMPXWRAPPERS_SPEC): Remove "--no-whole-archive" from
static-libmpxwrappers case.
(LIBMPX_SPEC): Add guards with MPX_LD_AS_NEEDED_GUARD_PUSH and
MPX_LD_AS_NEEDED_GUARD_POP.
* configure: Regenerate.
* configure.ac (HAVE_LD_PUSHPOPSTATE_SUPPORT): New variable.
defined if linker support "--push-state"/"--pop-state".

Modified:
trunk/gcc/ChangeLog
trunk/gcc/config.in
trunk/gcc/config/i386/linux-common.h
trunk/gcc/configure
trunk/gcc/configure.ac

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[ienkovich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

Ilya Enkovich  changed:

   What|Removed |Added

 CC||ienkovich at gcc dot gnu.org

--- Comment #3 from Ilya Enkovich  ---
(In reply to Sergey from comment #1)
>   Why can't we engage usual linkage mechanism by adding some undefined weak
> symbol   in mpx code and its definition in mpx library ? ( probably two
> different ones, for libmpx and libmpxwrappers ). Then we wouldn't have to
> juggle with (no-)as-needed.

How would we exactly use that symbol?  Is there any chance linker throw away
this weak symbol usage as unneeded?  This scheme looks like possible but
requires careful design.

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[peter at lekensteyn dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

Peter Wu  changed:

   What|Removed |Added

 CC||peter at lekensteyn dot nl

--- Comment #2 from Peter Wu  ---
Building Wireshark on Arch Linux with the -Wl,--as-needed linker option also
results in issues.

Example output during the linker stage (with -mmpx -fcheck-pointer-bounds):
/usr/lib/gcc/x86_64-pc-linux-gnu/6.2.1/../../../../lib/libmpxwrappers.so:
undefined reference to `get_bd'
collect2: error: ld returned 1 exit status

$ readelf -s /usr/lib/libmpxwrappers.so.2.0.0 | grep get_bd
 8:  0 NOTYPE  GLOBAL DEFAULT  UND get_bd
72:  0 NOTYPE  GLOBAL DEFAULT  UND get_bd
$ readelf -s /usr/lib/libmpx.so.2.0.0 | grep get_bd
38: 1720 8 FUNCGLOBAL DEFAULT   13 get_bd@@LIBMPX_2.0
   115: 1720 8 FUNCGLOBAL DEFAULT   13 get_bd

What helped here was explicitly adding -lmpxwrappers -lmpx to the linker flags.

[Bug target/77267] MPX does not work in a presence of "-Wl,-as-needed" option (Ubuntu default)

[saguryev.gnu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77267

Sergey  changed:

   What|Removed |Added

 CC||saguryev.gnu at gmail dot com

--- Comment #1 from Sergey  ---
  Why can't we engage usual linkage mechanism by adding some undefined weak
symbol   in mpx code and its definition in mpx library ? ( probably two
different ones, for libmpx and libmpxwrappers ). Then we wouldn't have to
juggle with (no-)as-needed.