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Re: [PATCH 2/9] tracing: MIPS: mcount.S: Fixup of the 32bit support with

To: Wu Zhangjin <wuzhangjin@gmail.com>
Subject: Re: [PATCH 2/9] tracing: MIPS: mcount.S: Fixup of the 32bit support with gcc 4.5
From: David Daney <david.s.daney@gmail.com>
Date: Wed, 12 May 2010 10:16:16 -0700
Cc: Ralf Baechle <ralf@linux-mips.org>, linux-mips <linux-mips@linux-mips.org>
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On 05/12/2010 06:23 AM, Wu Zhangjin wrote:
From: Wu Zhangjin<wuzhangjin@gmail.com>

As the doc[1] of gcc-4.5 shows, the -mmcount-ra-address uses register
$12 to transfer the stack offset of the return address to the _mcount
function. in 64bit kernel, $12 is t0, but in 32bit kernel, it is t4, so,
we need to use $12 instead of t0 here to cover the 64bit and 32bit
support.

[1] Gcc doc: MIPS Options
http://gcc.gnu.org/onlinedocs/gcc/MIPS-Options.html

Signed-off-by: Wu Zhangjin<wuzhangjin@gmail.com>

Would it be better to do?:

#define MCOUNT_RA_ADDRESS_REG $12

s/t0/MCOUNT_RA_ADDRESS_REG/g

David Daney

---
  arch/mips/kernel/mcount.S |   10 +++++-----
  1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index e256bf9..92d1540 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -69,7 +69,7 @@ _mcount:

        MCOUNT_SAVE_REGS
  #ifdef KBUILD_MCOUNT_RA_ADDRESS
-       PTR_S   t0, PT_R12(sp)  /* t0 saved the location of the return 
address(at) by -mmcount-ra-address */
+       PTR_S   $12, PT_R12(sp) /* $12 saved the location of the return 
address(at) by -mmcount-ra-address */
  #endif

        move    a0, ra          /* arg1: next ip, selfaddr */
@@ -135,7 +135,7 @@ NESTED(ftrace_graph_caller, PT_SIZE, ra)
  #ifdef CONFIG_DYNAMIC_FTRACE
        PTR_L   a1, PT_R31(sp)  /* load the original ra from the stack */
  #ifdef KBUILD_MCOUNT_RA_ADDRESS
-       PTR_L   t0, PT_R12(sp)  /* load the original t0 from the stack */
+       PTR_L   $12, PT_R12(sp) /* load the original $12 from the stack */
  #endif
  #else
        MCOUNT_SAVE_REGS
@@ -143,10 +143,10 @@ NESTED(ftrace_graph_caller, PT_SIZE, ra)
  #endif

  #ifdef KBUILD_MCOUNT_RA_ADDRESS
-       bnez    t0, 1f          /* non-leaf func: t0 saved the location of the 
return address */
+       bnez    $12, 1f         /* non-leaf func: $12 saved the location of the 
return address */
         nop
-       PTR_LA  t0, PT_R1(sp)   /* leaf func: get the location of at(old ra) 
from our own stack */
-1:     move    a0, t0          /* arg1: the location of the return address */
+       PTR_LA  $12, PT_R1(sp)  /* leaf func: get the location of at(old ra) 
from our own stack */
+1:     move    a0, $12         /* arg1: the location of the return address */
  #else
        PTR_LA  a0, PT_R1(sp)   /* arg1:&AT ->  a0 */
  #endif


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