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

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

On Thu, Jul 23, 2026 at 03:02:38PM +0530, Mukesh Kumar Chaurasiya wrote:
> On Wed, Jul 22, 2026 at 10:01:55AM +0300, Dmitry V. Levin wrote:
> > 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.
> > 
> [...]
> 
> Hey,
> 
> Can you try this fix? This should fix the ABI breakage.
[...]
> diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
> index a393b7f2760a..01e630149d48 100644
> --- a/arch/powerpc/include/uapi/asm/ptrace.h
> +++ b/arch/powerpc/include/uapi/asm/ptrace.h
> @@ -55,8 +55,6 @@ 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__ */
> @@ -116,12 +114,10 @@ struct pt_regs
>  #define PT_DAR	41
>  #define PT_DSISR 42
>  #define PT_RESULT 43
> -#define PT_EXIT_FLAGS 44
> -#define PT_PAD 47 /* 3 times */
> -#define PT_DSCR 48
> -#define PT_REGS_COUNT 48
> +#define PT_DSCR 44
> +#define PT_REGS_COUNT 44
>  
> -#define PT_FPR0	(PT_REGS_COUNT + 4)	/* each FP reg occupies 2 slots in this space */
> +#define PT_FPR0	48	/* each FP reg occupies 2 slots in this space */
>  
>  #ifndef __powerpc64__
>  
> @@ -133,7 +129,7 @@ struct pt_regs
>  #define PT_FPSCR (PT_FPR0 + 32)	/* each FP reg occupies 1 slot in 64-bit space */
>  
>  
> -#define PT_VR0	(PT_FPSCR + 2)	/* <82> each Vector reg occupies 2 slots in 64-bit */
> +#define PT_VR0 82	/* each Vector reg occupies 2 slots in 64-bit */
>  #define PT_VSCR (PT_VR0 + 32*2 + 1)
>  #define PT_VRSAVE (PT_VR0 + 33*2)
>  
> @@ -141,7 +137,7 @@ struct pt_regs
>  /*
>   * Only store first 32 VSRs here. The second 32 VSRs in VR0-31
>   */
> -#define PT_VSR0	(PT_VRSAVE + 2)	/* each VSR reg occupies 2 slots in 64-bit */
> +#define PT_VSR0 150	/* each VSR reg occupies 2 slots in 64-bit */
>  #define PT_VSR31 (PT_VSR0 + 2*31)
>  #endif /* __powerpc64__ */
>  

As this patch essentially reverts the uapi header to its v7.1 state,
the uapi part of the patch is definitely fine.


-- 
ldv