Re: [RFC PATCH v3 13/17] s390/ptrace: Provide frame_pointer()

Heiko Carstens
2025-12-10T15:19:56Z

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@linux.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.