linux-kernel - Re: [RFC PATCH v3 13/17] s390/ptrace: Provide frame

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Message-ID: <20251210151902.40732D1a-hca@linux.ibm.com>
Date: Wed, 10 Dec 2025 16:19:02 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Jens Remus <jremus@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-s390@...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>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...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>,
        Florian Weimer <fweimer@...hat.com>, Kees Cook <kees@...nel.org>,
        "Carlos O'Donell" <codonell@...hat.com>, Sam James <sam@...too.org>,
        Dylan Hatch <dylanbhatch@...gle.com>
Subject: Re: [RFC PATCH v3 13/17] s390/ptrace: Provide frame_pointer()

On Mon, Dec 08, 2025 at 06:15:55PM +0100, Jens Remus wrote:
> On s390 64-bit the s390x ELF ABI [1] designates register 11 as the
> "preferred" frame pointer (FP) register in user space.
> 
> While at it convert instruction_pointer() and user_stack_pointer()
> from macros to inline functions, to align their definition with
> x86 and arm64.
> 
> Use const qualifier on struct pt_regs pointers to prevent compiler
> warnings:
> 
> arch/s390/kernel/stacktrace.c: In function ‘arch_stack_walk_user_common’:
> arch/s390/kernel/stacktrace.c:114:34: warning: passing argument 1 of
> ‘instruction_pointer’ discards ‘const’ qualifier from pointer target
> type [-Wdiscarded-qualifiers]
> ...
> arch/s390/kernel/stacktrace.c:117:48: warning: passing argument 1 of
> ‘user_stack_pointer’ discards ‘const’ qualifier from pointer target
> type [-Wdiscarded-qualifiers]
> ...
> 
> [1]: s390x ELF ABI, https://github.com/IBM/s390x-abi/releases
> 
> Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
> ---
> 
> Notes (jremus):
>     Changes in RFC v2:
>     - Separate provide frame_pointer() into this new commit.
> 
>  arch/s390/include/asm/ptrace.h | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h
> index dfa770b15fad..455c119167fc 100644
> --- a/arch/s390/include/asm/ptrace.h
> +++ b/arch/s390/include/asm/ptrace.h
> @@ -212,8 +212,6 @@ void update_cr_regs(struct task_struct *task);
>  #define arch_has_block_step()	(1)
>  
>  #define user_mode(regs) (((regs)->psw.mask & PSW_MASK_PSTATE) != 0)
> -#define instruction_pointer(regs) ((regs)->psw.addr)
> -#define user_stack_pointer(regs)((regs)->gprs[15])
>  #define profile_pc(regs) instruction_pointer(regs)

"while at it", and then you don't convert user_mode() to a function? :)

Please provide a stand-alone patch for the "while at it" stuff, so it
can go independently.