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DateWed, 21 Oct 2009 17:14:37 +0400
FromSergei Shtylyov <>
SubjectRe: ftrace for MIPS
Hello.

Steven Rostedt wrote:

>>Need to check which registers is missing when saving/restoring for
>>_mcount:

>>NESTED(ftrace_graph_caller, PT_SIZE, ra)
>> MCOUNT_SAVE_REGS
>> PTR_S v0, PT_R2(sp)
>>
>> MCOUNT_SET_ARGS
>> jal prepare_ftrace_return
>> nop
>>
>> /* overwrite the parent as &return_to_handler: v0 -> $1(at) */
>> move $1, v0

> I'm confused here? I'm not exactly sure what the above is doing. Is $1 a
> register (AT)?

Yes.

> And how is this register used before calling mcount?

>> PTR_L v0, PT_R2(sp)
>> MCOUNT_RESTORE_REGS
>> RETURN_BACK
>> END(ftrace_graph_caller)

>> .align 2
>> .globl return_to_handler
>>return_to_handler:
>> PTR_SUBU sp, PT_SIZE
>> PTR_S v0, PT_R2(sp)

> BTW, is v0 the only return register? I know x86 can return two different
> registers depending on what it returns. What happens if a function
> returns a 64 bit value on a 32bit box? Does it use two registers for
> that?

Yes, there's also v1 register.

WBR, Sergei


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