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Revert "build-sys: drop -mms-bitfields GCC flag"

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This reverts commit 252bbcd2078aadc67a49bacd5b2cd4fd348a8dd7.

After further discussion in !3511, we’ve decided that there are risks
associated with this change, and it’s not the best way of addressing the
original problem.

The original motivation for the change turned out to be that
`-mms-bitfields` was not handled by `windres`, which was receiving it
from `pkg-config --cflags glib-2.0` in some projects. However, if
`windres` is claiming to accept CFLAGS then it should accept (and
ignore) `-mms-bitfields`, since the `-m` family of options are defined
in `man gcc`, just like `-I`, `-D`, etc.

There is some question that there might still be third party projects
which are built with an old enough compiler that `-mms-bitfields` is not
the compiler default. For that reason, we should either still continue
to specify `-mms-bitfields` in the `.pc` file, or add a test to assert
that third party projects are always compiled with `-mms-bitfields` set.
But adding a new test for all third-party compilations is risky (if we
get it wrong, things will break; and it’s a test which may behave
differently on different platforms), so it seems safer to just keep
`-mms-bitfields` in `.pc` for now.

Once all compilers which we require specify `-mms-bitfields` by default,
we can finally drop this flag (without adding a test for third-party
compilations).

See: https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3511
This commit is contained in:
Philip Withnall 2023-07-29 11:54:22 +03:00
parent 6e77bb3315
commit 627dc1415c
3 changed files with 13 additions and 5 deletions
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8
docs/win32-build.md
View File

@ -65,10 +65,10 @@ Building software that just *uses* GLib or GTK also require to have
the right compiler set up the right way. If you intend to use MinGW-GCC,
follow the relevant instructions below in that case, too.
You should link to GLib using the `-mms-bitfields` GCC flag. It is the default
since 2012 (GCC 4.7). This flag means that the struct layout rules are identical
to those used by MSVC. This is essential if the same DLLs are to be usable both
from gcc- and MSVC-compiled code.
You should link to GLib using the `-mms-bitfields` GCC flag. This flag means
that the struct layout rules are identical to those used by MSVC. This is
essential if the same DLLs are to be usable both from gcc- and MSVC-compiled
code.
## Cross-CRT issues

2
glib/meson.build
View File

@ -443,7 +443,7 @@ pkg.generate(libglib,
libraries : [libintl_deps],
libraries_private : [win32_ldflags],
subdirs : ['glib-2.0'],
extra_cflags : ['-I${libdir}/glib-2.0/include'],
extra_cflags : ['-I${libdir}/glib-2.0/include'] + win32_cflags,
variables : [
'bindir=' + '${prefix}' / get_option('bindir'),
'datadir=' + '${prefix}' / get_option('datadir'),

8
meson.build
View File

@ -50,6 +50,7 @@ if cc.get_id() == 'msvc'
noseh_link_args = ['/SAFESEH:NO']
else
noseh_link_args = []
# -mms-bitfields vs -fnative-struct ?
endif
host_system = host_machine.system()
@ -2351,8 +2352,15 @@ else
export_dynamic_ldflags = ['-Wl,--export-dynamic']
endif
win32_cflags = []
win32_ldflags = []
if host_system == 'windows' and cc.get_id() != 'msvc' and cc.get_id() != 'clang-cl'
# Ensure MSVC-compatible struct packing convention is used when
# compiling for Win32 with gcc. It is used for the whole project and exposed
# in glib-2.0.pc.
win32_cflags = ['-mms-bitfields']
add_project_arguments(win32_cflags, language : 'c')
# Win32 API libs, used only by libglib and exposed in glib-2.0.pc
win32_ldflags = ['-lws2_32', '-lole32', '-lwinmm', '-lshlwapi', '-luuid']
elif host_system == 'cygwin'