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flag-o-matic.eclass: simplify implementation and work in all cases

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It curently uses some magic test to decide whether handcrafted code
works with or without -latomic. But it can claim that -latomic is not
needed for that case, while it is still needed for other cases.

> okay so append-atomic-flags does not work for me in this case
> noise-suppression-for-voice is doing `struct RnNoiseStats { uint32_t a, b, c, d; }; std::atomic<RnNoiseStats> m_stats;`
> not just a single large integer

It is simplest to always add -latomic when an ebuild gets that deep
feeling that yeah, it would like some atomics please. The downsides to
listing a linker library are exactly:

- it might be unavailable
- it might be unneeded

And the former case is trivial to solve -- this function already does so
-- while the latter case has a sanctioned approach that is already used
for other intrinsic compiler libraries, but not for atomic "because the
build system would have a hard time if we had to build atomic early on"
which isn't a very good reason to break ebuilds which aren't building
sys-devel/gcc.

As a side benefit, we now handle -latomic such that a package which
requires it, but only for parts of the installed package, does not
overlink to libatomic in *all* binaries/libraries, even if the default
LDFLAGS are overridden and the global -Wl,--as-needed disappears.

Bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81358
Bug: https://bugs.gentoo.org/820101
Bug: https://bugs.gentoo.org/925672
Signed-off-by: Eli Schwartz <eschwartz93@gmail.com>
Signed-off-by: Sam James <sam@gentoo.org>
This commit is contained in:
Eli Schwartz
2024-03-27 23:47:10 -04:00
committed by Sam James
parent 1bca889879
commit ec90f4c3a4
1 changed files with 18 additions and 60 deletions
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78
eclass/flag-o-matic.eclass
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@@ -1015,69 +1015,27 @@ test-compile() {
}
# @FUNCTION: append-atomic-flags
# @USAGE: [bytes]
# @DESCRIPTION:
# Attempts to detect if appending -latomic is required to use
# a specific-sized atomic intrinsic, and if so, appends it. If the bytesize
# is not specified, then check the four most common byte sizes (1, 2, 4, 8).
# >=16-byte atomics are not included in this default set and must be explicitly
# passed if required. This may require you to add a macro definition like
# -Duint128_t=__uint128_t to your CFLAGS.
# Attempts to detect if appending -latomic works, and does so.
append-atomic-flags() {
# this implementation is as described in bug #820101
local code
# Make sure that the flag is actually valid. If it isn't, then maybe the
# library both doesn't exist and is redundant, or maybe the toolchain is
# broken, but let the build succeed or fail on its own.
test-flags-CCLD "-latomic" &>/dev/null || return
# first, ensure we can compile a trivial program
# this is because we can't distinguish if test-compile
# fails because -latomic is actually needed or if we have a
# broken toolchain (like due to bad FLAGS)
read -r -d '' code <<- EOF
int main(void)
{
return 0;
}
EOF
# if toolchain is broken, just return silently. it's better to
# let other pieces of the build fail later down the line than to
# make people think that something to do with atomic support is the
# cause of their problems.
test-compile "c+ld" "${code}" || return
local bytesizes
[[ "${#}" == "0" ]] && bytesizes=( "1" "2" "4" "8" ) || bytesizes="${@}"
for bytesize in ${bytesizes[@]}
do
# this sample program is informed by the great testing from the buildroot project:
# https://github.com/buildroot/buildroot/commit/6856e417da4f3aa77e2a814db2a89429af072f7d
read -r -d '' code <<- EOF
#include <stdint.h>
int main(void)
{
uint$((${bytesize} * 8))_t a = 0;
__atomic_add_fetch(&a, 3, __ATOMIC_RELAXED);
__atomic_compare_exchange_n(&a, &a, 2, 1, __ATOMIC_RELAXED, __ATOMIC_RELAXED);
return 0;
}
EOF
# do nothing if test program links fine
test-compile "c+ld" "${code}" && continue
# ensure that the toolchain supports -latomic
test-flags-CCLD "-latomic" &>/dev/null || die "-latomic is required but not supported by $(tc-getCC)"
append-libs "-latomic"
# verify that this did indeed fix the problem
test-compile "c+ld" "${code}" || \
die "libatomic does not include an implementation of ${bytesize}-byte atomics for this toolchain"
# if any of the required bytesizes require -latomic, no need to continue
# checking the others
return
done
# We unconditionally append this flag. In the case that it's needed, the
# flag is, well, needed. In the case that it's not needed, it causes no
# harm, because we ensure that this specific library is definitely
# certainly linked with as-needed.
#
# Really, this should be implemented directly in the compiler, including
# the use of push/pop for as-needed. It's exactly what the gcc spec file
# does for e.g. -lgcc_s, but gcc is concerned about doing so due to build
# system internals and as a result all users have to deal with this mess
# instead.
#
# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81358
append-libs "-Wl,--push-state,--as-needed,-latomic,--pop-state"
}
fi