Re: [PATCH, v2] Expect SI_KERNEL or TRAP_BRKPT si_code values for MIPS breakpoint traps

[Pedro Alves <palves@redhat.com>]

On 02/22/2016 04:19 PM, Maciej W. Rozycki wrote:
> On Mon, 22 Feb 2016, Pedro Alves wrote:
> 
>> I'd like to have a short paragraph in linux-nat.h about MIPS's behavior,
>> below the ppc comment.  If you look at the x86 table above, which cases get
>> SI_KERNEL, and which don't?  Single-step is not applicable, since the
>> MIPS doesn't handle single-stepping itself (IIRC), but do we also get
>> SI_KERNEL hardware bps and watchpoints, for example?
> 
>  As I previously noted the MIPS Linux port currently does not support 
> hardware breakpoints even though hardware may have them implemented 
> (they're optional).  Only hardware watchpoints are supported right now.

Ah.

>  You are right in that there's no OS single-stepping support defined in 
> the MIPS architecture and consequently Linux cannot support it on the MIPS 
> target.  Only JTAG single-stepping is possible with MIPS hardware.

Yeah.  I see I missed a word, sorry.  I meant
"since the MIPS _kernel_ doesn't handle single-stepping itself".

I was thinking about e.g., uprobes, and imagining that since the kernel
needs to advance past uprobes-set breakpoints somehow, that the kernel
could have learned to software single-step, and that that might have been
hooked to PTRACE_SINGLESTEP.

Thanks,
Pedro Alves