Hi Alice,
> On 16 Jul 2026, at 16:06, Alice Carlotti <[email protected]> wrote:
>
> On Thu, Oct 26, 2023 at 08:31:04PM +0100, Iain Sandoe wrote:
>> This is an enablement patch (the initial use comes with the Darwin aarch64
>> port). Tested on aarch64-linux-gnu, aarch64-apple-darwin and x86_64-darwin
>> just for good measure, OK for trunk?
>> thanks
>> Iain.
>>
>> --- 8< ---
>>
>> Some assmblers have a bug that requires +crc to be emitted even
>> though the base architecture supports it. However, that also
>> triggers a different bug in another assembler. So make the fix
>> configurable.
>
> I only just noticed this, sorry, but I don't think it's as straightforward as
> "triggers a different bug in another assembler". It's actually "avoids
> triggering one bug in another assembler, which means we hit a different bug in
> that assembler more often". I described the bugs in detail in
> https://gcc.gnu.org/pipermail/gcc-patches/2025-January/674446.html.
>
> There's no sensible way to workaround both of those bugs at the same time.
> The
> effect of this patch is that some .arch directives will be ignored, instead of
> being applied with missing features. In some cases this helps (if the .arch
> directive includes unrecognised feature names that will be incorrectly
> dropped,
> and there are no recognised optional features specified). In other cases
> (likely much rarer), this patch makes things worse (if the .arch directive
> specifies a higher architecture version, with only the mandatory architecture
> features present).
>
> Given that the broken Binutils versions don't support Darwin, I think it's
> fine
> to disable the CRC workaround when targetting Darwin, or if we otherwise know
> that we're using an old LLVM version for assembly. This will improve the
> likelihood of being able to assemble the resulting output with LLVM <=16, but
> it's still going to break sometimes, and realistically the best option is to
> avoid using LLVM <=16 (or other assemblers without the LLVM 17 fixes) for
> assembly if at all possible.
>
> To be clear - I have no objection to this patch remaining in (or being
> replaced
> with a patch that disables the workaround for Darwin), but I wanted to make
> clear that the situation is more nuanced than your commit message suggests.
As things stand, the DISABLE_AARCH64_AS_CRC_BUGFIX is only set in
my (currently out-of-tree) development branch for aarch64-darwin:
aarch64-*-darwin* )
tm_file="${tm_file} aarch64/aarch64-errata.h"
tmake_file="${tmake_file} aarch64/t-aarch64 aarch64/t-aarch64-darwin"
tm_defines="${tm_defines} TARGET_DEFAULT_ASYNC_UNWIND_TABLES=1"
tm_defines="${tm_defines} DISABLE_AARCH64_AS_CRC_BUGFIX=1"
# Choose a default CPU version that will work for all current releases.
with_cpu=${with_cpu:-apple-m1}
;;
I guess that linux ports could detect an LLVM version (we already do this in
gcc/configure for Darwin, since there are other dependencies) and then apply
the same for earlier versions?
Maybe I’m mixing up negatives;
Are you saying the if Darwin is using an assembler based on LLVM >= 17 then
the fix can be left in place and llvm backend will cope OK?
I ask because this also has some impact on the testsuite - which i’m in the
process
of tidying on the journey to posting the port …
Iain
>
> Alice
>
>
>>
>> gcc/ChangeLog:
>>
>> * common/config/aarch64/aarch64-common.cc: Make the asm
>> crc bug workaround configurable.
>>
>> Signed-off-by: Iain Sandoe <[email protected]>
>> ---
>> gcc/common/config/aarch64/aarch64-common.cc | 8 ++++++--
>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/gcc/common/config/aarch64/aarch64-common.cc
>> b/gcc/common/config/aarch64/aarch64-common.cc
>> index 20bc4e1291b..4922a6b235c 100644
>> --- a/gcc/common/config/aarch64/aarch64-common.cc
>> +++ b/gcc/common/config/aarch64/aarch64-common.cc
>> @@ -301,8 +301,12 @@ aarch64_get_extension_string_for_isa_flags
>>
>> However, assemblers with Armv8-R AArch64 support should not have this
>> issue, so we don't need this fix when targeting Armv8-R. */
>> - auto explicit_flags = (!(current_flags & AARCH64_FL_V8R)
>> - ? AARCH64_FL_CRC : 0);
>> + aarch64_feature_flags explicit_flags =
>> +#ifndef DISABLE_AARCH64_AS_CRC_BUGFIX
>> + (!(current_flags & AARCH64_ISA_V8R) ? AARCH64_FL_CRC : 0);
>> +#else
>> + 0;
>> +#endif
>>
>> /* Add the features in isa_flags & ~current_flags using the smallest
>> possible number of extensions. We can do this by iterating over the
>> --
>> 2.39.2 (Apple Git-143)
>>
