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

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

[Thorsten Leemhuis]

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
on my table. I can only look briefly into most of them. Unfortunately
therefore I sometimes will get things wrong or miss something important.
I hope that's not the case here; if you think it is, don't hesitate to
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
this mail to get things rolling again and hence don't need to be CC on
all further activities wrt to this regression.

---
Additional information about regzbot:

If you want to know more about regzbot, check out its web-interface, the
getting start guide, and/or the references documentation:

https://linux-regtracking.leemhuis.info/regzbot/
https://gitlab.com/knurd42/regzbot/-/blob/main/docs/getting_started.md
https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md

The last two documents will explain how you can interact with regzbot
yourself if your want to.

Hint for reporters: when reporting a regression it's in your interest to
tell #regzbot about it in the report, as that will ensure the regression
gets on the radar of regzbot and the regression tracker. That's in your
interest, as they will make sure the report won't fall through the
cracks unnoticed.

Hint for developers: you normally don't need to care about regzbot once
it's involved. Fix the issue as you normally would, just remember to
include a 'Link:' tag to the report in the commit message, as explained
in Documentation/process/submitting-patches.rst
That aspect was recently was made more explicit in commit 1f57bd42b77c:
https://git.kernel.org/linus/1f57bd42b77c

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

[Thorsten Leemhuis]

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

TWIMC: this mail is primarily send for documentation purposes and for
regzbot, my Linux kernel regression tracking bot. These mails usually
contain '#forregzbot' in the subject, to make them easy to spot and filter.

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
> on my table. I can only look briefly into most of them. Unfortunately
> therefore I sometimes will get things wrong or miss something important.
> I hope that's not the case here; if you think it is, don't hesitate to
> 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
> this mail to get things rolling again and hence don't need to be CC on
> all further activities wrt to this regression.
> 
> ---
> Additional information about regzbot:
> 
> If you want to know more about regzbot, check out its web-interface, the
> getting start guide, and/or the references documentation:
> 
> https://linux-regtracking.leemhuis.info/regzbot/
> https://gitlab.com/knurd42/regzbot/-/blob/main/docs/getting_started.md
> https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md
> 
> The last two documents will explain how you can interact with regzbot
> yourself if your want to.
> 
> Hint for reporters: when reporting a regression it's in your interest to
> tell #regzbot about it in the report, as that will ensure the regression
> gets on the radar of regzbot and the regression tracker. That's in your
> interest, as they will make sure the report won't fall through the
> cracks unnoticed.
> 
> Hint for developers: you normally don't need to care about regzbot once
> it's involved. Fix the issue as you normally would, just remember to
> include a 'Link:' tag to the report in the commit message, as explained
> in Documentation/process/submitting-patches.rst
> That aspect was recently was made more explicit in commit 1f57bd42b77c:
> https://git.kernel.org/linus/1f57bd42b77c