Re: [PATCH -tip -v10 5/7] x86: add pt_regs register and stack access APIs

Masami Hiramatsu
2009-07-06T19:25:58Z

Andi Kleen wrote:
> Masami Hiramatsu <mhiramat@redhat.com> writes:
>
>> Add following APIs for accessing registers and stack entries from pt_regs.
>
> You forgot to state who calls these functions/why are they added?
> Who only has strings for registers?

Oh, yes. This patch is needed for kprobes based event tracer on ftrace.
Some other debugging tools might be able to use it.

> I can see the point of having a function for nth argument though,
> that's useful.
>
>> +static inline unsigned long regs_get_argument_nth(struct pt_regs *regs,
>> + unsigned n)
>> +{
>> + if (n < NR_REGPARMS) {
>> + switch (n) {
>> + case 0:
>> + return regs->ax;
>> + case 1:
>> + return regs->dx;
>> + case 2:
>> + return regs->cx;
>
>
> [....]
>
> That could be done shorter with a offsetof table.
>
>> + if (n < NR_REGPARMS) {
>> + switch (n) {
>> + case 0:
>> + return regs->di;
>> + case 1:
>> + return regs->si;
>> + case 2:
>> + return regs->dx;
>> + case 3:
>> + return regs->cx;
>> + case 4:
>> + return regs->r8;
>> + case 5:
>> + return regs->r9;
>
> and that too.

I'm not so sure about your idea.
Would you mean below code?

int offs_table[NR_REGPARMS] = {
[0] = offsetof(struct pt_regs, di),
...
};
if (n < NR_REGPARMS)
return *((unsigned long *)regs + offs_table[n]);

Thank you,