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SubjectRe: [PATCH 1/2] MIPS: ftrace.h: Fix the MCOUNT_INSN_SIZE definition
On 09/22/2014 06:32 AM, Markos Chandras wrote:
> The MCOUNT_INSN_SIZE is meant to be used to denote the overall
> size of the mcount() call. Since a jal instruction is used to
> call mcount() the delay slot should be taken into consideration
> as well.
> This also replaces the MCOUNT_INSN_SIZE usage with the real size
> of a single MIPS instruction since, as described above, the
> MCOUNT_INSN_SIZE is used to denote the total overhead of the
> mcount() call.

Are you seeing errors with the existing code? If so please state what
they are.

By changing this, we can no longer atomically replace the instruction.
So I think shouldn't be changing this stuff unless there is a real bug
we are fixing.

In conclusion: NAK unless the patch fixes a bug, in which case the
change log *must* state what the bug is, and how the patch addresses the
problem.

David Daney


>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
> ---
> arch/mips/include/asm/ftrace.h | 2 +-
> arch/mips/kernel/ftrace.c | 4 +++-
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/mips/include/asm/ftrace.h b/arch/mips/include/asm/ftrace.h
> index 992aaba603b5..70d4a35fb560 100644
> --- a/arch/mips/include/asm/ftrace.h
> +++ b/arch/mips/include/asm/ftrace.h
> @@ -13,7 +13,7 @@
> #ifdef CONFIG_FUNCTION_TRACER
>
> #define MCOUNT_ADDR ((unsigned long)(_mcount))
> -#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
> +#define MCOUNT_INSN_SIZE 8 /* sizeof mcount call + delay slot */
>
> #ifndef __ASSEMBLY__
> extern void _mcount(void);
> diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
> index 937c54bc8ccc..211460d4617d 100644
> --- a/arch/mips/kernel/ftrace.c
> +++ b/arch/mips/kernel/ftrace.c
> @@ -28,6 +28,8 @@
> #define MCOUNT_OFFSET_INSNS 4
> #endif
>
> +#define FTRACE_MIPS_INSN_SIZE 4 /* Size of single MIPS instruction */
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> /* Arch override because MIPS doesn't need to run this from stop_machine() */
> @@ -395,7 +397,7 @@ void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
> */
>
> insns = in_kernel_space(self_ra) ? 2 : MCOUNT_OFFSET_INSNS + 1;
> - trace.func = self_ra - (MCOUNT_INSN_SIZE * insns);
> + trace.func = self_ra - (FTRACE_MIPS_INSN_SIZE * insns);
>
> /* Only trace if the calling function expects to */
> if (!ftrace_graph_entry(&trace)) {
>



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