Failure in elf/tst-pie-address{, -static} on aarch64 with PAC/BTI release.

[Sam James]

Sam James <sam@gentoo.org> writes:

> Adhemerval Zanella Netto <adhemerval.zanella@linaro.org> writes:
>
>> On 15/01/25 19:42, Aurelien Jarno wrote:
>>> Hi,
>>> 
>>> Commit e7b553272196 ("elf: Handle static PIE with non-zero load address
>>> [BZ #31799]") added two news tests, elf/tst-pie-address and
>>> elf/tst-pie-address-static. In my test builds for glibc 2.41, they fail
>>> on aarch64 when PAC/BTI is enabled with the current HEAD.
>>> elf/tst-pie-address fails with a SIGSEGV and elf/tst-pie-address-static
>>> with a SIGILL.
>>> 
>>> This has been fixed by commit bce70034b112 ("elf: Check PDE load address
>>> with non-empty text section") for the non-PAC/BTI case, but I still
>>> observe the tests failures with PAC/BTI enabled in the compiler. This is
>>> on a CPU which does not support PAC/BTI and which should interpret the
>>> corresponding instructions as nop. I have tested building glibc with
>>> both binutils 2.43.1 and 2.43.50.20250108 and both gcc 13.3.0 and gcc
>>> 14.2.0.
>>> 
>>> This can be reproduced with (at least here) with:
>>> 
>>> CC="gcc -mbranch-protection=standard" CXX="g++ -mbranch-protection=standard" ../glibc/configure --prefix=/usr && make -j4 && make -j4 check
>>> 
>>> Any idea?
>>
>> I can reproduce it with binutils 2.43.1, but it seems a ld.bfd issue.
>> Building with -Ttext-segment=0x0000000000400000 I see unusual PLT stubs
>> being generated:
>>
>> $ objdump -D --section .plt elf/tst-pie-address
>> [...]
>> 0000000000401a40 <memcpy@plt>:
>>   401a40:       90000010        adrp    x16, 401000 <__abi_tag+0xce0>
>>   401a44:       f90000f1        str     x17, [x7]
>>   401a48:       91000210        add     x16, x16, #0x0
>>   401a4c:       d6000220        .inst   0xd6000220 ; undefined
>>   401a50:       90000010        adrp    x16, 401000 <__abi_tag+0xce0>
>>   401a54:       f90000f1        str     x17, [x7]
>> [...]
>>
>> Where with same link command, but without -Ttext-segment=, it shows the
>> expected stub instructions:
>>
>> $ objdump -D --section .plt elf/tst-pie-address-no-text-segment:
>> [...]
>> 0000000000001a40 <memcpy@plt>:
>>     1a40:       f00000f0        adrp    x16, 20000 <memcpy@GLIBC_2.17>
>>     1a44:       f9400211        ldr     x17, [x16]
>>     1a48:       91000210        add     x16, x16, #0x0
>>     1a4c:       d61f0220        br      x17
>>
>> Also, lld seems to generate correct binary (with its analogous --image-base
>> option).
>
> Can you file a binutils bug ASAP, given the release is planned soon
> (branching on Sunday)? Thanks.

Sorry for the ambiguity: I mean the upcoming binutils-2.44 release.