Re: Unable to set $xmm2-9 registers but able to set $xmm0-1,10-15 with ptrace syscall (fwd from bugzilla) #forregzbot

[Thorsten Leemhuis <regressions@leemhuis.info>]

For the record:

#regzbot fixed-by 44cad52cc14ae10062f142e
#regzbot ignore-activity

https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=44cad52cc14ae10062f142ec16ede489bccf4469

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On 26.01.22 08:39, Thorsten Leemhuis wrote:
> Hi, this is your Linux kernel regression tracker speaking.
> 
> There is a regression dealt with in bugzilla I'd like to add to the
> tracking:
> 
> #regzbot introduced: 6164331d15f7d912fb9369245368e9564ea49813
> #regzbot from: Luís Ferreira <contact@lsferreira.net>
> #regzbot link: https://bugzilla.kernel.org/show_bug.cgi?id=215524
> 
> Quote:
> 
>> Writing some XMM registers on a process with `ptrace` syscall with `PTRACE_SETREGSET` request and using `NT_FPREGSET` is broken. Although, when using `NT_X86_XSTATE` works just fine. Also, getting the registers with `PTRACE_GETREGSET` is fine too.
>>
>> This can be considered a blocker for old hardware that lacks AVX extensions and simply fail to call ptrace with `NT_X86_XSTATE`. This particularly failed the testsuite of LLDB on my server.
>>
>> I've tested this on Linux 5.16.2, Linux LTS 5.15.16 and Linux LTS 5.10.93. Only the last one (5.10.93) succeeded with `NT_FPREGSET`. I tested this in a clean installation of Arch Linux with the official packages and backported version of Linux LTS, available in AUR repository.
>>
>> Note: I didn't test `NT_FPREGSET` on recent hardware (hardware with AVX).
>>
>> From my investigation on the issue and the kernel source code inspection, I believe that this was introduced here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/kernel/fpu/regset.c?id=6164331d15f7d912fb9369245368e9564ea49813
>>
>> I'm going to leave a reference to some issues/patches on GDB and LLDB debuggers to either reproduce the issue and see some logs I created with strace:
>> - https://reviews.llvm.org/D117928
>> - https://sourceware.org/bugzilla/show_bug.cgi?id=28803
> 
> Ciao, Thorsten (wearing his 'Linux kernel regression tracker' hat)
> 
> P.S.: As a Linux kernel regression tracker I'm getting a lot of reports
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> tell me about it in a public reply, that's in everyone's interest.
> 
> BTW, I have no personal interest in this issue, which is tracked using
> regzbot, my Linux kernel regression tracking bot
> (https://linux-regtracking.leemhuis.info/regzbot/). I'm only posting
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> all further activities wrt to this regression.
> 
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