Default autotools CFLAGS are overriden in some cases

[Alfonso Sanchez-Beato]

snapcraft overrides CFLAGS in case the staged packages pull files under folders "include", "usr/include", etc. In that case CFLAGS is of the form:

CFLAGS= -I<part_dir>/install/usr/include -I<part_dir>/usr/include/x86_64-linux-gnu ...

But, that overrides autotools defaults, which are

CFLAGS=-g -O2

Therefore, inadvertently we disable all optimizations. Even more, things can go weird and in some cases one part is built with "-g -O2", while the others are not. For instance, with the modem-manager snap:

https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/modem-manager/tree/snapcraft.yaml

where libmbim is compiled with "-g -O2" while the other parts are not, as there are headers in "stage" folder.

[Sergio Schvezov (sergiusens)]

We should either keep default CFLAGS when adding our own or provide our own set of defaults applied to all projects

[Jim Hodapp (jhodapp)]

@sergio: I heard this is implemented already, should this be fix committed or even fix released?

[Alfonso Sanchez-Beato (alfonsosanchezbeato)]

@sergiusens, so, what has been the solution for this?

[Alfonso Sanchez-Beato (alfonsosanchezbeato)]

I think the solution here would be to append the "-I <folder>" directives to CFLAGS instead of overriding it.

[Sergio Schvezov (sergiusens)]

This seems to be standard behavior, if we do this, we have no way to override the defaults, no matter what you set. I know snapcraft sets the CFLAGS for you, but we really do not know what the defaults are going to be for a project as those could be set per project.

Introducing this change now has the potential to cause unexpected side effects, I also believe that what you probably want is "dpkg-buildflags --get CFLAGS".

We can set that as a default for core24 if desired, which is still on grade devel.

If field is willing to accept the potential support burden on potentially having builds break, I am more than happy to set a fixed default for CFLAGS on older bases, such that the following could break:

"""
    If using the GNU C compiler, set shell variable GCC to ‘yes’. If output variable CFLAGS was not already set, set it to -g -O2 for the GNU C compiler (-O2 on systems where GCC does not accept -g), or -g for other compilers. If your package does not like this default, then it is acceptable to insert the line

    : ${CFLAGS=""}

    after AC_INIT and before AC_PROG_CC to select an empty default instead.
"""

[Launchpad Janitor (janitor)]

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