On Thu, 2009-10-22 at 11:34 -0700, David Daney wrote: > Wu Zhangjin wrote: > > On Wed, 2009-10-21 at 11:24 -0400, Steven Rostedt wrote: > [...] > >>> + > >>> +NESTED(_mcount, PT_SIZE, ra) > >>> + RESTORE_SP_FOR_32BIT > >>> + PTR_LA t0, ftrace_stub > >>> + PTR_L t1, ftrace_trace_function /* please don't use t1 later, safe? */ > >> Is t0 and t1 safe for mcount to use? Remember, mcount does not follow > >> the dynamics of C function ABI. > > > > So, perhaps we can use the saved registers(a0,a1...) instead. > > > > a0..a7 may not always be saved. > > You can use at, v0, v1 and all the temporary registers. Note that for > the 64-bit ABIs sometimes the names t0-t4 shadow a4-a7. So for a 64-bit > kernel, you can use: $1, $2, $3, $12, $13, $14, $15, $24, $25, noting > that at == $1 and contains the callers ra. For a 32-bit kernel you can > add $8, $9, $10, and $11 before the profiling source code(jal _mcount), there are only necessary stack operations, nobody have touched the GPRs, so, I think we are safe to use any of them, that's why the t0,t1 I have used not fail. and 'Cause the a0,a1 is used as the arguments to the real profiling function, so, I will keep back to use t0, t1, as David Daney said $12, $13 in 64bit and $8, $9 in 32bit. Thanks! Regards, Wu Zhangjin
