MIPS: Ftrace: Fix function tracing return address to match

Dynamic function tracing was not working on MIPS.  When doing dynamic
tracing, the tracer attempts to match up the passed in address with
the one the compiler creates in the mcount tables.  The MIPS code was
passing in the return address from the tracing function call, but the
compiler tables were the address of the function call.  So they
wouldn't match.

Just subtracting 8 from the return address will give the address of
the function call.  Easy enough.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
[david.daney@cavium.com: Adjusted code comment and patch Subject.]
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/5592/

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index a03e93c4a94634b786c873f41e8b2f56846bad26..539b6294b613c84fcff1286d267c4b7a5aba401c 100644 (file)
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -83,7 +83,7 @@ _mcount:
        PTR_S   MCOUNT_RA_ADDRESS_REG, PT_R12(sp)
 #endif
 
-       move    a0, ra          /* arg1: self return address */
+       PTR_SUBU a0, ra, 8      /* arg1: self address */
        .globl ftrace_call
 ftrace_call:
        nop     /* a placeholder for the call to a real tracing function */