Re: [PATCH v7 3/8] Use xml-syscall to compare syscall numbers in arm_linux_sigreturn_return-addr.

Antoine Tremblay
2015-12-11T13:04:55Z

On 12/11/2015 07:47 AM, Pedro Alves wrote:
> On 12/11/2015 12:31 PM, Antoine Tremblay wrote:
>>
>>
>> On 12/11/2015 07:05 AM, Pedro Alves wrote:
>>> On 12/11/2015 12:02 PM, Yao Qi wrote:
>>>> On 11/12/15 11:59, Pedro Alves wrote:
>>>>> but then you might as well just do:
>>>>>
>>>>> #define ARM_SIGRETURN 119
>>>>
>>>> How about using __NR_sigreturn and __NR_rt_sigreturn directly? like
>>>> what patch #6 does.
>>>
>>> Those are host/native macros. Only make sense for the running host.
>>> Can't use that in a tdep file, like arm-linux-tdep.c. Otherwise, e.g.,
>>> a x86-hosted cross debugger would be using the x86 __NR_sigreturn, etc.
>>>
>>
>> Exactly that's why I use those only in GDBServer.
>
> Hmm, actually, that sounds wrong.
>
> What about Aarch64 gdbserver debugging Aarch32?
>
> I see that the new code in question in patch #6 is in gdbserver/linux-arm-low.c,
> which is not built on Aarch64, but, shouldn't that new arm_sigreturn_next_pc
> code be used in the biarch scenario as well?
>

This is only used if we need software single stepping, I think in that
case hardware single stepping will be used on aarch64 even if stepping
over an arm32 program, Yao can confirm ?

> If you just made that 32-bit-specific code compile on Aarch64 it would
> be compiling against Aarch64's __NR_sigreturn, which I'd assume is wrong for Aarch32.
>
>>

Looking at the kernel code in linux/arch/arm64 I see :

include/asm/unistd.h:#define __NR_compat_sigreturn 119
include/asm/unistd.h:#define __NR_compat_rt_sigreturn 173

include/asm/unistd32.h:#define __NR_sigreturn 119
include/asm/unistd32.h:__SYSCALL(__NR_sigreturn,
compat_sys_sigreturn_wrapper)

include/asm/unistd32.h:#define __NR_rt_sigreturn 173
include/asm/unistd32.h:__SYSCALL(__NR_rt_sigreturn,
compat_sys_rt_sigreturn_wrapper)

So I think it's ok... but I can't compile on aarch64 at the moment.

>> Personally while I like the #define ARM_SIGRETURN 119 better, I think
>> the xml function is fine.
>>
>
> If you added
>
> #define ARM_LINUX_SIGRETURN 119
>
> to arch/arm-linux.h
>
> you could use it in both places.

That was my first thought, I would be OK with that if Yao is too,
however I think both methods work.