Re: [PATCH 1/3] libgcc: Mark AArch64 asm features with build attributes

On 30/07/2026 16:06, Andreas Schwab wrote:
> On Mai 21 2026, Muhammad Kamran wrote:
> 
>> @@ -92,14 +91,39 @@
>>     .word 0;				\
>>     .previous
>>   
>> +#ifdef __ARM_BUILDATTR64_FV
>> +/* Add AArch64 feature bits build attributes.  */
>> +# define FEATURE_1_AND_MARK(value)					\
>> +    .aeabi_subsection aeabi_feature_and_bits, optional, ULEB128;	\
>> +    .if ((value) & FEATURE_1_BTI);					\
>> +    .aeabi_attribute Tag_Feature_BTI, 1;				\
>> +    .else;								\
>> +    .aeabi_attribute Tag_Feature_BTI, 0;				\
>> +    .endif;								\
>> +    .if ((value) & FEATURE_1_PAC);					\
>> +    .aeabi_attribute Tag_Feature_PAC, 1;				\
>> +    .else;								\
>> +    .aeabi_attribute Tag_Feature_PAC, 0;				\
>> +    .endif;								\
>> +    .if ((value) & FEATURE_1_GCS);					\
>> +    .aeabi_attribute Tag_Feature_GCS, 1;				\
>> +    .else;								\
>> +    .aeabi_attribute Tag_Feature_GCS, 0;				\
>> +    .endif;								\
>> +    .previous
> 
> This does not work.  The .previous directive will not undo the
> .aeabi_subsection switch, instead it will switch to the .note.GNU-stack
> section ...
> 
>> +#else
>> +/* Add a NT_GNU_PROPERTY_TYPE_0 note.  */
>> +# define FEATURE_1_AND_MARK(value) GNU_PROPERTY (FEATURE_1_AND, value)
>> +#endif
>> +
>>   #if defined(__linux__) || defined(__FreeBSD__)
>>   /* Do not require executable stack.  */
>>   .section .note.GNU-stack, "", %progbits
>>   .previous
> 
> ... which was temporarily entered here.  Thus all the rest of the code
> will end up there instead of .text.
> 

Thanks, you're right.  I incorrectly treated .aeabi_subsection like a
normal .section switch that could be undone with .previous.  I'll drop
the .previous from the __ARM_BUILDATTR64_FV FEATURE_1_AND_MARK
definition and leave section restoration only in the GNU_PROPERTY path,
where it matches the explicit .section switch.

Thanks,
Kamran

>> -/* Add GNU property note if built with branch protection.  */
>> +/* Add marking if built with branch protection.  */
>>   # if (BTI_FLAG|PAC_FLAG|GCS_FLAG) != 0
>> -GNU_PROPERTY (FEATURE_1_AND, BTI_FLAG|PAC_FLAG|GCS_FLAG)
>> +FEATURE_1_AND_MARK (BTI_FLAG|PAC_FLAG|GCS_FLAG)
>>   # endif
>>   #endif
>