linux-kernel - Re: [RFC PATCH v1 11/16] s390/unwind_user/sframe: Enable HAVE_UNWIND_USER

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Message-ID: <8b9a66b5-8b9f-410a-a072-7b9ba72ef7c3@linux.ibm.com>
Date: Fri, 1 Aug 2025 17:46:33 +0200
From: Jens Remus <jremus@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        bpf@...r.kernel.org, x86@...nel.org,
        Steven Rostedt <rostedt@...nel.org>, Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>,
        Sam James <sam@...too.org>
Subject: Re: [RFC PATCH v1 11/16] s390/unwind_user/sframe: Enable
 HAVE_UNWIND_USER_SFRAME

On 8/1/2025 2:53 PM, Heiko Carstens wrote:
> On Thu, Jul 10, 2025 at 06:35:17PM +0200, Jens Remus wrote:

>> +static inline void __s390_get_dwarf_fpr(unsigned long *val, int regnum)
>> +{
>> +	switch (regnum) {
>> +	case 16:
>> +		fpu_std(0, (freg_t *)val);
>> +		break;
> 
> ...
> 
>> +static inline int s390_unwind_user_get_reg(unsigned long *val, int regnum)
>> +{
>> +	if (0 <= regnum && regnum <= 15) {
>> +		struct pt_regs *regs = task_pt_regs(current);
>> +		*val = regs->gprs[regnum];
>> +	} else if (16 <= regnum && regnum <= 31) {
>> +		__s390_get_dwarf_fpr(val, regnum);
> 
> This won't work with other potential in-kernel fpu users. User space fpr
> contents may have been written to the current task's fpu save area and fprs
> may have been clobbered by in-kernel users; so you need to get register
> contents from the correct location. See arch/s390/include/asm/fpu.h.

Thanks!  Will implement all the review feedback and send a RFC V2 once I
am back from vacation.  Will be away from keyboard for a few weeks.

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@...ibm.com

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