Re: Wrong order of preprocessor and compiler flags

[Evgeny Grin]

Hello Alex,

On 28.03.2022 4:55, Alex Ameen wrote:
This is a message I meant send to "all", I'm sending again for the wider 
discussion.


Please let me know if my understanding of include order is incorrect. 
Essentially I'm more concerned about relative placement of `AM_CPPFLAGS' 
and `CPPFLAGS' in any future changes.


Moving CPPFLAGS to the end of the line prevents users from overriding 
include paths.


Currently flags are used in automake as
AM_CPPFLAGS CPPFLAGS AM_CFLAGS CFLAGS

Actually, there is *no way* to override include path defined in 
AM_CPPFLAGS (unless AM_CPPFLAGS is redefined in command line, which is 
not right way). Any include search paths defined in CPPFLAGS and in 
CFLAGS will be added to the end of the search list.


On the other hand, this is a right thing. As defined in the same section 
of the GNU Coding Standards [1], there are two types of flags. The first 
type is flags required for proper compilation.
For example: when building library, I need root of build path for the 
lib's "configure.h" and the lib's includes directory. They must be the 
first items in the include search path, like

AM_CPPFLAGS="-I../../builddir -I../lib/include"
If user will override (prepend) with "-I/usr/include 
-I/usr/include/polly/Config" it would break the compilation, because 
lib's installed header will be used instead of header in sources dir and 
polly's config.h will be found first instead of lib's config.h.


I believe it's current placement is intended to provide an avenue for 
overrides in the same way that CFLAGS being at the end allows users to 
override the C standards and spec flags.


Really what I care about is the relative order of `CPPFLAGS 
AM_CPPFLAGS', and `AM_CFLAGS CFLAGS' - whether these groups are ordered 
before or after the other group is less important though. For example 
I'm content with either `CPPFLAGS AM_CPPFLAGS AM_CFLAGS CFLAGS' or 
`AM_CFLAGS CFLAGS CPPFLAGS AM_CPPFLAGS'.


My suggestion with "AM_CFLAGS AM_CPPFLAGS CFLAGS CPPFLAGS" gives user 
the same level of freedom on flags overriding as current "AM_CPPFLAGS 
CPPFLAGS AM_CFLAGS CFLAGS", CFLAGS still override any AM_* flags, and 
order of used flags is the same as tested by "configure".



[1] https://www.gnu.org/prep/standards/standards.html#Command-Variables

--
Evgeny

On Sun, Mar 27, 2022, 5:00 PM Jan Engelhardt > wrote:



On Sunday 2022-03-27 23:22, Karl Berry wrote:

 >It seems the basic inconsistency is whether CPPFLAGS is considered a
 >"user variable" or not. In earlier eras, it wasn't [...]

In earlier eras of what exactly?

As for make, it never made a distinction between user variables or
otherwise,
at least that's the way make comes across. Some software will just
break on `make CFLAGS=-O3` and others will work to compile.

As for automake, AM_CPPFLAGS was introduced at the same time as
AM_CFLAGS as
per the git log. So CPPFLAGS always was a user variable.

 >[more on CFLAGS<->CPPFLAGS order]

I went to the GNU make git repo to check on CPPFLAGS; it appeared
first in
documentation rather than source (which seems like a history import
mishap),
but even back then in '94, the documentation was inconsistent, sometimes
providing example descriptions where CPPFLAGS comes after
CFLAGS/FFLAGS/etc.,
and sometimes reversed.



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Re: Wrong order of preprocessor and compiler flags

[Evgeny Grin]

Hello Karl,


On 28.03.2022 0:22, Karl Berry wrote:

It seems the basic inconsistency is whether CPPFLAGS is considered a
"user variable" or not. In earlier eras, it wasn't, but from your msg,
I gather it is now.

The GNU standards node about it, that you mentioned,
   https://www.gnu.org/prep/standards/standards.html#Command-Variables
does not clearly state it one way or another. But its example shows
CFLAGS after CPPFLAGS.


The same example puts "-I." into ALL_CFLAGS, which makes even harder to 
guess the right idea how to use CPPFLAGS.



Thus I think a prior step is to write bug-standa...@gnu.org and suggest
clarifying the status of CPPFLAGS, its relationship to CFLAGS, etc.


Definitely makes sense.
I'll write to the standards list.


We could consider changing automake to follow autoconf even if the GCS
is not changed, but it would be better if the GCS were clear.

 2. Use AM_CFLAGS CFLAGS AM_CPPFLAGS CPPFLAGS. This is more aligned with
 current flags grouping, but CFLAGS will not override definitions in
 AM_CPPFLAGS (less aligned with GNU Standards).

It seems wrong (and disastrously backwards-incompatible) to me for
CFLAGS not to override AM_everything. Your option 1:

 1. Use AM_CFLAGS AM_CPPFLAGS CFLAGS CPPFLAGS. I think this is the best
 option. As required by GNU Standards, CFLAGS still override all
 upstream-defined flags.

seems like the best option to me too. --thanks, karl.


--
Evgeny

Re: Wrong order of preprocessor and compiler flags

[Alex Ameen]

This is a message I meant send to "all", I'm sending again for the wider
discussion.

Please let me know if my understanding of include order is incorrect.
Essentially I'm more concerned about relative placement of `AM_CPPFLAGS'
and `CPPFLAGS' in any future changes.

Moving CPPFLAGS to the end of the line prevents users from overriding
include paths.

I believe it's current placement is intended to provide an avenue for
overrides in the same way that CFLAGS being at the end allows users to
override the C standards and spec flags.

Really what I care about is the relative order of `CPPFLAGS AM_CPPFLAGS',
and `AM_CFLAGS CFLAGS' - whether these groups are ordered before or after
the other group is less important though. For example I'm content with
either `CPPFLAGS AM_CPPFLAGS AM_CFLAGS CFLAGS' or `AM_CFLAGS CFLAGS
CPPFLAGS AM_CPPFLAGS'.


On Sun, Mar 27, 2022, 5:00 PM Jan Engelhardt  wrote:

>
> On Sunday 2022-03-27 23:22, Karl Berry wrote:
>
> >It seems the basic inconsistency is whether CPPFLAGS is considered a
> >"user variable" or not. In earlier eras, it wasn't [...]
>
> In earlier eras of what exactly?
>
> As for make, it never made a distinction between user variables or
> otherwise,
> at least that's the way make comes across. Some software will just
> break on `make CFLAGS=-O3` and others will work to compile.
>
> As for automake, AM_CPPFLAGS was introduced at the same time as AM_CFLAGS
> as
> per the git log. So CPPFLAGS always was a user variable.
>
> >[more on CFLAGS<->CPPFLAGS order]
>
> I went to the GNU make git repo to check on CPPFLAGS; it appeared first in
> documentation rather than source (which seems like a history import
> mishap),
> but even back then in '94, the documentation was inconsistent, sometimes
> providing example descriptions where CPPFLAGS comes after
> CFLAGS/FFLAGS/etc.,
> and sometimes reversed.
>

Re: Wrong order of preprocessor and compiler flags

[Bob Friesenhahn]

On Mon, 28 Mar 2022, Jan Engelhardt wrote:


I went to the GNU make git repo to check on CPPFLAGS; it appeared first in
documentation rather than source (which seems like a history import mishap),
but even back then in '94, the documentation was inconsistent, sometimes
providing example descriptions where CPPFLAGS comes after CFLAGS/FFLAGS/etc.,
and sometimes reversed.


I think that this is because it was always assumed that the order does 
not matter.


Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
Public Key, http://www.simplesystems.org/users/bfriesen/public-key.txt

Re: Wrong order of preprocessor and compiler flags

[Jan Engelhardt]

On Sunday 2022-03-27 23:22, Karl Berry wrote:

>It seems the basic inconsistency is whether CPPFLAGS is considered a
>"user variable" or not. In earlier eras, it wasn't [...]

In earlier eras of what exactly?

As for make, it never made a distinction between user variables or otherwise,
at least that's the way make comes across. Some software will just
break on `make CFLAGS=-O3` and others will work to compile.

As for automake, AM_CPPFLAGS was introduced at the same time as AM_CFLAGS as
per the git log. So CPPFLAGS always was a user variable.

>[more on CFLAGS<->CPPFLAGS order]

I went to the GNU make git repo to check on CPPFLAGS; it appeared first in
documentation rather than source (which seems like a history import mishap),
but even back then in '94, the documentation was inconsistent, sometimes
providing example descriptions where CPPFLAGS comes after CFLAGS/FFLAGS/etc.,
and sometimes reversed.

Re: Wrong order of preprocessor and compiler flags

[Karl Berry]

It seems the basic inconsistency is whether CPPFLAGS is considered a
"user variable" or not. In earlier eras, it wasn't, but from your msg,
I gather it is now.

The GNU standards node about it, that you mentioned,
  https://www.gnu.org/prep/standards/standards.html#Command-Variables
does not clearly state it one way or another. But its example shows
CFLAGS after CPPFLAGS.

Thus I think a prior step is to write bug-standa...@gnu.org and suggest
clarifying the status of CPPFLAGS, its relationship to CFLAGS, etc.

We could consider changing automake to follow autoconf even if the GCS
is not changed, but it would be better if the GCS were clear.

2. Use AM_CFLAGS CFLAGS AM_CPPFLAGS CPPFLAGS. This is more aligned with 
current flags grouping, but CFLAGS will not override definitions in 
AM_CPPFLAGS (less aligned with GNU Standards).

It seems wrong (and disastrously backwards-incompatible) to me for
CFLAGS not to override AM_everything. Your option 1:

1. Use AM_CFLAGS AM_CPPFLAGS CFLAGS CPPFLAGS. I think this is the best 
option. As required by GNU Standards, CFLAGS still override all 
upstream-defined flags.

seems like the best option to me too. --thanks, karl.