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Re: Strace doesn't work on linux-2.4.28 and later

To: David Daney <ddaney@avtrex.com>
Subject: Re: Strace doesn't work on linux-2.4.28 and later
From: Ralf Baechle <ralf@linux-mips.org>
Date: Mon, 7 Feb 2005 21:08:25 +0000
Cc: andreev <andreev@niisi.msk.ru>, linux-mips@linux-mips.org
In-reply-to: <4207C3E0.7070405@avtrex.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <41FF876B.3070407@niisi.msk.ru> <4207C142.6070804@avtrex.com> <4207C3E0.7070405@avtrex.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.4.1i
On Mon, Feb 07, 2005 at 11:39:12AM -0800, David Daney wrote:

> >    offset("#define PT_SCRATCH0 ", struct pt_regs, pad0[4]);
> >    offset("#define PT_SCRATCH1 ", struct pt_regs, pad0[5]);
> >
> >I am thinking of testing a patch where I change them to:
> >
> >    offset("#define PT_SCRATCH0 ", struct pt_regs, pad0[0]);
> >    offset("#define PT_SCRATCH1 ", struct pt_regs, pad0[1]);
> >
> >Any needed argument registers are already saved in and restored from the 
> >regs array so overwriting the stack area reserved for them should be OK.
> >
> I now think that is bogus reasoning as the first four slots can be 
> clobbered by the compiler.
> 
> It seems that t2 must be saved somewhere in the regs list.  I am not 
> sure what the problem with PT_R1(sp) was, but it seems like a good 
> candidate.  Perhaps PT_R26 or PT_R27 (k0, k1) would be a better place to 
> store t2 as I don't think k0 or k1 are ever stored.

I was always planning to backport the newer fix from 2.6 which is simply
storing the value in a caller saved register.  You now reminded me of
that omission ;-)

Patch below,

  Ralf

Index: arch/mips/kernel/scall_o32.S
===================================================================
RCS file: /home/cvs/linux/arch/mips/kernel/Attic/scall_o32.S,v
retrieving revision 1.18.2.14
diff -u -r1.18.2.14 scall_o32.S
--- arch/mips/kernel/scall_o32.S        25 Nov 2004 09:43:59 -0000      
1.18.2.14
+++ arch/mips/kernel/scall_o32.S        7 Feb 2005 21:12:53 -0000
@@ -121,15 +121,14 @@
 
 trace_a_syscall:
        SAVE_STATIC
-       sw      t2, PT_SCRATCH0(sp)
+       move    s0, sp
        jal     syscall_trace
-       lw      t2, PT_SCRATCH0(sp)
 
        lw      a0, PT_R4(sp)           # Restore argument registers
        lw      a1, PT_R5(sp)
        lw      a2, PT_R6(sp)
        lw      a3, PT_R7(sp)
-       jalr    t2
+       jalr    s0
 
        li      t0, -EMAXERRNO - 1      # error?
        sltu    t0, t0, v0
Index: arch/mips/tools/offset.c
===================================================================
RCS file: /home/cvs/linux/arch/mips/tools/Attic/offset.c,v
retrieving revision 1.16.4.12
diff -u -r1.16.4.12 offset.c
--- arch/mips/tools/offset.c    25 Nov 2004 09:43:59 -0000      1.16.4.12
+++ arch/mips/tools/offset.c    7 Feb 2005 21:12:53 -0000
@@ -12,7 +12,6 @@
 #include <linux/types.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
-#include <linux/signal.h>
 
 #include <asm/ptrace.h>
 #include <asm/processor.h>
@@ -37,9 +36,6 @@
 void output_ptreg_defines(void)
 {
        text("/* MIPS pt_regs offsets. */");
-       offset("#define PT_SCRATCH0 ", struct pt_regs, pad0[4]);
-       offset("#define PT_SCRATCH1 ", struct pt_regs, pad0[5]);
-
        offset("#define PT_R0     ", struct pt_regs, regs[0]);
        offset("#define PT_R1     ", struct pt_regs, regs[1]);
        offset("#define PT_R2     ", struct pt_regs, regs[2]);
Index: arch/mips64/kernel/scall_64.S
===================================================================
RCS file: /home/cvs/linux/arch/mips64/kernel/Attic/scall_64.S,v
retrieving revision 1.20.2.20
diff -u -r1.20.2.20 scall_64.S
--- arch/mips64/kernel/scall_64.S       25 Nov 2004 09:43:59 -0000      
1.20.2.20
+++ arch/mips64/kernel/scall_64.S       7 Feb 2005 21:12:53 -0000
@@ -102,15 +102,14 @@
 
 trace_a_syscall:
        SAVE_STATIC
-       sd      t2, PT_SCRATCH0(sp)
+       move    s0, t2
        jal     syscall_trace
-       ld      t2, PT_SCRATCH0(sp)
 
        ld      a0, PT_R4(sp)           # Restore argument registers
        ld      a1, PT_R5(sp)
        ld      a2, PT_R6(sp)
        ld      a3, PT_R7(sp)
-       jalr    t2
+       jalr    s0
 
        li      t0, -EMAXERRNO - 1      # error?
        sltu    t0, t0, v0
Index: arch/mips64/kernel/scall_n32.S
===================================================================
RCS file: /home/cvs/linux/arch/mips64/kernel/Attic/scall_n32.S,v
retrieving revision 1.2.2.17
diff -u -r1.2.2.17 scall_n32.S
--- arch/mips64/kernel/scall_n32.S      25 Nov 2004 09:43:59 -0000      1.2.2.17
+++ arch/mips64/kernel/scall_n32.S      7 Feb 2005 21:12:53 -0000
@@ -106,15 +106,14 @@
 
 trace_a_syscall:
        SAVE_STATIC
-       sd      t2, PT_SCRATCH0(sp)
+       move    s0, t2
        jal     syscall_trace
-       ld      t2, PT_SCRATCH0(sp)
 
        ld      a0, PT_R4(sp)           # Restore argument registers
        ld      a1, PT_R5(sp)
        ld      a2, PT_R6(sp)
        ld      a3, PT_R7(sp)
-       jalr    t2
+       jalr    s0
 
        li      t0, -EMAXERRNO - 1      # error?
        sltu    t0, t0, v0
Index: arch/mips64/kernel/scall_o32.S
===================================================================
RCS file: /home/cvs/linux/arch/mips64/kernel/Attic/scall_o32.S,v
retrieving revision 1.48.2.33
diff -u -r1.48.2.33 scall_o32.S
--- arch/mips64/kernel/scall_o32.S      25 Nov 2004 09:43:59 -0000      
1.48.2.33
+++ arch/mips64/kernel/scall_o32.S      7 Feb 2005 21:12:53 -0000
@@ -118,9 +118,8 @@
        sd      a6, PT_R10(sp)
        sd      a7, PT_R11(sp)
 
-       sd      t2, PT_SCRATCH0(sp)
+       move    s0, t2
        jal     syscall_trace
-       ld      t2, PT_SCRATCH0(sp)
 
        ld      a0, PT_R4(sp)           # Restore argument registers
        ld      a1, PT_R5(sp)
@@ -129,7 +128,7 @@
        ld      a4, PT_R8(sp)
        ld      a5, PT_R9(sp)
 
-       jalr    t2
+       jalr    s0
 
        li      t0, -EMAXERRNO - 1      # error?
        sltu    t0, t0, v0

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