Hi, 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. I mean I have saved/restored them as the _mcount of /lib/libc.so.6 for MIPS did, so I can use them safely. > > 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 > In a generic function, they should be okay, but _mcount is a little specific. so, Not sure these rules are suitable to it or not. > This whole thing seems a little fragile. > > I think it might be a good idea to get input from Richard Sandiford, > and/or Adam Nemet about this approach (so I add them to the CC). > > This e-mail thread starts here: > > http://www.linux-mips.org/archives/linux-mips/2009-10/msg00286.html > > and here: > > http://www.linux-mips.org/archives/linux-mips/2009-10/msg00290.html looking forward to their reply, thanks! Regards! Wu Zhangjin
