[PATCH] powerpc: Add missing registers to clobbers list for syscalls [BZ #27623]

[PATCH] powerpc: Add missing registers to clobbers list for syscalls [BZ #27623]

[Matheus Castanho]

Some registers that can be clobbered by the kernel during a syscall are not
listed on the clobbers list in sysdeps/unix/sysv/linux/powerpc/sysdep.h.

For syscalls using sc:
    - XER is zeroed by the kernel on exit

For syscalls using scv:
    - XER is zeroed by the kernel on exit
    - Different from the sc case, most CR fields can be clobbered (according to
      the ELF ABI and the Linux kernel's syscall ABI for powerpc
      (linux/Documentation/powerpc/syscall64-abi.rst)

These are likely not causing issues today, but they should be added to the
clobbers list just in case things change on the kernel side in the future.

Reported-by: Nicholas Piggin <npiggin@gmail.com>
---
 sysdeps/unix/sysv/linux/powerpc/sysdep.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/powerpc/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/sysdep.h
index 6b99464e61..d15e80d610 100644
--- a/sysdeps/unix/sysv/linux/powerpc/sysdep.h
+++ b/sysdeps/unix/sysv/linux/powerpc/sysdep.h
@@ -86,7 +86,8 @@
 	 "=&r" (r6), "=&r" (r7), "=&r" (r8)	\
        : ASM_INPUT_##nr			\
        : "r9", "r10", "r11", "r12",		\
-	 "lr", "ctr", "memory");		\
+	 "cr0", "cr1", "cr5", "cr6", "cr7",	\
+	 "xer", "lr", "ctr", "memory"); 	\
     r3;					\
   })
 
@@ -101,7 +102,7 @@
 	 "=&r" (r6), "=&r" (r7), "=&r" (r8)	\
        : ASM_INPUT_##nr			\
        : "r9", "r10", "r11", "r12",		\
-	 "cr0", "ctr", "memory");		\
+	 "xer", "cr0", "ctr", "memory");	\
     r0 & (1 << 28) ? -r3 : r3;			\
   })
 
-- 
2.30.2

Re: [PATCH] powerpc: Add missing registers to clobbers list for syscalls [BZ #27623]

[Andreas Schwab]

On Mär 22 2021, Matheus Castanho via Libc-alpha wrote:

> Some registers that can be clobbered by the kernel during a syscall are not
> listed on the clobbers list in sysdeps/unix/sysv/linux/powerpc/sysdep.h.
>
> For syscalls using sc:
>     - XER is zeroed by the kernel on exit
>
> For syscalls using scv:
>     - XER is zeroed by the kernel on exit
>     - Different from the sc case, most CR fields can be clobbered (according to
>       the ELF ABI and the Linux kernel's syscall ABI for powerpc
>       (linux/Documentation/powerpc/syscall64-abi.rst)
>
> These are likely not causing issues today, but they should be added to the
> clobbers list just in case things change on the kernel side in the future.

What about INTERNAL_VSYSCALL_CALL_TYPE?  Doesn't that clobber XER[CA]
and CR1/5/6/7 like ordinary function calls?

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH] powerpc: Add missing registers to clobbers list for syscalls [BZ #27623]

[Matheus Castanho]

Andreas Schwab <schwab@linux-m68k.org> writes:

> On Mär 22 2021, Matheus Castanho via Libc-alpha wrote:
>
>> Some registers that can be clobbered by the kernel during a syscall are not
>> listed on the clobbers list in sysdeps/unix/sysv/linux/powerpc/sysdep.h.
>>
>> For syscalls using sc:
>>     - XER is zeroed by the kernel on exit
>>
>> For syscalls using scv:
>>     - XER is zeroed by the kernel on exit
>>     - Different from the sc case, most CR fields can be clobbered (according to
>>       the ELF ABI and the Linux kernel's syscall ABI for powerpc
>>       (linux/Documentation/powerpc/syscall64-abi.rst)
>>
>> These are likely not causing issues today, but they should be added to the
>> clobbers list just in case things change on the kernel side in the future.
>
> What about INTERNAL_VSYSCALL_CALL_TYPE?  Doesn't that clobber XER[CA]
> and CR1/5/6/7 like ordinary function calls?
>
> Andreas.

Yes, looks like they should be added to the clobbers list there too. I'll send
a v2 shortly.

--
Matheus Castanho