Re: [PATCH v4 5/8] powerpc: add exit_flags field in pt_regs

["Dmitry V. Levin" <ldv@strace.io>]

On Fri, Jan 23, 2026 at 01:09:13PM +0530, Mukesh Kumar Chaurasiya wrote:
> From: Mukesh Kumar Chaurasiya <mchauras@linux.ibm.com>
> 
> Add a new field `exit_flags` in the pt_regs structure. This field will hold
> the flags set during interrupt or syscall execution that are required during
> exit to user mode.

Apparently, this change breaks PTRACE_GETREGS as the latter has no means
to communicate the size of struct pt_regs being written to userspace.

As result, the kernel with this patch will write to userpsace 32 more
bytes than before, and unless the userspace is re-compiled with the latest
ptrace.h, 32 bytes of userspace memory after struct pt_regs will be
overwritten.

This issue was detected by strace test suite, specifically, the test that
checks whether the actual number of bytes written by
ptrace(PTRACE_GETREGS) matches sizeof(struct pt_regs), and that test failed
with runtime version v7.1 and headers version v7.2-rc1.

> diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
> index 01e630149d48..a393b7f2760a 100644
> --- a/arch/powerpc/include/uapi/asm/ptrace.h
> +++ b/arch/powerpc/include/uapi/asm/ptrace.h
> @@ -55,6 +55,8 @@ struct pt_regs
>  	unsigned long dar;		/* Fault registers */
>  	unsigned long dsisr;		/* on 4xx/Book-E used for ESR */
>  	unsigned long result;		/* Result of a system call */
> +	unsigned long exit_flags;	/* System call exit flags */
> +	unsigned long __pt_regs_pad[3];	/* Maintain 16 byte interrupt stack alignment */
>  };
>  
>  #endif /* __ASSEMBLER__ */

-- 
ldv