Re: [PATCH 06/10] ARM: ftrace: add Thumb-2 support

Catalin Marinas
2010-02-13T23:27:32Z

Rabin Vincent wrote:
> Fix the mcount routines to build and run on a kernel built with the
> Thumb-2 instruction set.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Rabin Vincent <rabin@rab.in>
> ---
> arch/arm/kernel/entry-common.S | 8 +++++---
> 1 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 42eb166..cd2a574 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -156,7 +156,8 @@ ENTRY(__gnu_mcount_nc)
> stmdb sp!, {r0-r3, lr}
> ldr r0, =ftrace_trace_function
> ldr r2, [r0]
> - adr r0, ftrace_stub
> + THUMB( orr r2, r2, #1 )
> + adr r0, BSYM(ftrace_stub)
> cmp r0, r2

Does this code not give the correct result if not modified?

> bne gnu_trace
> ldmia sp!, {r0-r3, ip, lr}
> @@ -166,8 +167,9 @@ gnu_trace:
> ldr r1, [sp, #20] @ lr of instrumented routine
> mov r0, lr
> sub r0, r0, #MCOUNT_INSN_SIZE
> - mov lr, pc
> - mov pc, r2
> + ARM( mov lr, pc )
> + ARM( mov pc, r2 )
> + THUMB( blx r2 )
> ldmia sp!, {r0-r3, ip, lr}
> mov pc, ip
> ENDPROC(__gnu_mcount_nc)

As above, what does this need modifying? "mov pc, r2" wouldn't change
the mode to ARM even if the value in r2 is even. It may need THUMB(nop)
after this instruction.

I could of course miss something as I haven't actually tried this code.

--
Catalin