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    Subject[PATCH 06/10] ARM: ftrace: add Thumb-2 support
    Date
    Fix the mcount routines to build and run on a kernel built with the
    Thumb-2 instruction set:

    - Without the BSYM, the following assembler errors appear:

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

    - Without the orr, the lsb is not set on the pointer loaded from
    ftrace_trace_function, but is set on BSYM(ftrace_stub), leading to the
    comparison failing even when the pointer is pointing to ftrace_stub.

    - The problem with the "mov lr, pc", is that it does not set the lsb when
    storing the pc in lr. The called function returns with "bx lr", and the
    mode changes to ARM. The blx is to avoid this.

    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 c3bdb05..573ed3b 100644
    --- a/arch/arm/kernel/entry-common.S
    +++ b/arch/arm/kernel/entry-common.S
    @@ -167,7 +167,8 @@ 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
    bne gnu_trace
    ldmia sp!, {r0-r3, ip, lr}
    @@ -177,8 +178,9 @@ 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)
    --
    1.7.0


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