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
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
David Daney
Regards!
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