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SubjectRe: [PATCH 06/10] ARM: ftrace: add Thumb-2 support
On Tue, Mar 16, 2010 at 10:23:54AM +0000, Catalin Marinas wrote:
> If the ftrace_stub isn't .globl, the code compiles fine. My approach
> would be something like this:

New patch below:

From bf828a0c069b1bb3f6bf4e68f1dceecab396c286 Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabin@rab.in>
Date: Sun, 14 Feb 2010 01:18:34 +0530
Subject: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

Fix the mcount routines to build and run on a kernel built with the
Thumb-2 instruction set by correcting the following errors using the
fixes suggested by Catalin Marinas:

- Problem: The following assembler errors appear at the "adr r0,
ftrace_stub" instruction:

entry-common.S: Assembler messages:
entry-common.S:179: Error: invalid immediate for address calculation (value = 0x00000004)

Fix: The errors don't occur with a non-global symbol, so use one.

- Problem: The "mov lr, pc" does not set the lsb when storing the pc in
lr. The called function returns with "bx lr", and the mode changes
to ARM.

Fix: Add a label on the return address and use "adr lr, BSYM(label)".

We don't modify the old mcount because it won't be built when using
Thumb-2.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Rabin Vincent <rabin@rab.in>
---
arch/arm/kernel/entry-common.S | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index c7a8c20..f5e75de 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -167,7 +167,7 @@ ENTRY(__gnu_mcount_nc)
stmdb sp!, {r0-r3, lr}
ldr r0, =ftrace_trace_function
ldr r2, [r0]
- adr r0, ftrace_stub
+ adr r0, .Lftrace_stub
cmp r0, r2
bne gnu_trace
ldmia sp!, {r0-r3, ip, lr}
@@ -177,8 +177,9 @@ gnu_trace:
ldr r1, [sp, #20] @ lr of instrumented routine
mov r0, lr
sub r0, r0, #MCOUNT_INSN_SIZE
- mov lr, pc
+ adr lr, BSYM(1f)
mov pc, r2
+1:
ldmia sp!, {r0-r3, ip, lr}
mov pc, ip
ENDPROC(__gnu_mcount_nc)
@@ -213,6 +214,7 @@ ENDPROC(mcount)
#endif /* CONFIG_DYNAMIC_FTRACE */

ENTRY(ftrace_stub)
+.Lftrace_stub:
mov pc, lr
ENDPROC(ftrace_stub)

--
1.7.0


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