Re: [RFC 2/2] MIPS: tracing/ftrace: Fixes mcount_regex for modules

[David Daney <ddaney@caviumnetworks.com>]

On 10/22/2010 01:58 PM, Wu Zhangjin wrote:
> From: Wu Zhangjin<wuzhangjin@gmail.com>
>
> In some situations(with related kernel config and gcc options), the
> modules may have the same address space as the core kernel space, so
> mcount_regex for modules should also match R_MIPS_26.
>

I think Steve is rewriting this bit to be a pure C program.  Is this 
file even used anymore?  If so for how long?

David Daney

> Signed-off-by: Wu Zhangjin<wuzhangjin@gmail.com>
> ---
>   scripts/recordmcount.pl |   46 +++++++++++++++++++++++++++++-----------------
>   1 files changed, 29 insertions(+), 17 deletions(-)
>
> diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
> index e67f054..e9c1a0f 100755
> --- a/scripts/recordmcount.pl
> +++ b/scripts/recordmcount.pl
> @@ -299,14 +299,33 @@ if ($arch eq "x86_64") {
>       $cc .= " -m64";
>       $objcopy .= " -O elf64-sparc";
>   } elsif ($arch eq "mips") {
> -    # To enable module support, we need to enable the -mlong-calls option
> -    # of gcc for module, after using this option, we can not get the real
> -    # offset of the calling to _mcount, but the offset of the lui
> -    # instruction or the addiu one. herein, we record the address of the
> -    # first one, and then we can replace this instruction by a branch
> -    # instruction to jump over the profiling function to filter the
> -    # indicated functions, or swith back to the lui instruction to trace
> -    # them, which means dynamic tracing.
> +    #<For kernel>
> +    # To disable tracing, just replace "jal _mcount" with nop;
> +    # to enable tracing, replace back. so, the offset 14 is
> +    # needed to be recorded.
> +    #
> +    #     10:   03e0082d        move    at,ra
> +    #     14:   0c000000        jal     0
> +    #                    14: R_MIPS_26   _mcount
> +    #                    14: R_MIPS_NONE *ABS*
> +    #                    14: R_MIPS_NONE *ABS*
> +    #     18:   00020021        nop
> +    #
> +    #<For module>
> +    #
> +    # If no long call(-mlong-calls), the same to kernel.
> +    #
> +    # If the module space differs from the kernel space, long
> +    # call is needed, as a result, the address of _mcount is
> +    # needed to be recorded in a register and then jump from
> +    # module space to kernel space via "jalr<register>". To
> +    # disable tracing, "jalr<register>" can be replaced by
> +    # nop; to enable tracing, replace it back. Since the
> +    # offset of "jalr<register>" is not easy to be matched,
> +    # the offset of the 1st _mcount below is recorded and to
> +    # disable tracing, "lui v1, 0x0" is substituted with "b
> +    # label", which jumps over "jalr<register>"; to enable
> +    # tracing, replace it back.
>       #
>       #       c:	3c030000 	lui	v1,0x0
>       #			c: R_MIPS_HI16	_mcount
> @@ -318,19 +337,12 @@ if ($arch eq "x86_64") {
>       #			10: R_MIPS_NONE	*ABS*
>       #      14:	03e0082d 	move	at,ra
>       #      18:	0060f809 	jalr	v1
> +    #   label:
>       #
> -    # for the kernel:
> -    #
> -    #     10:   03e0082d        move    at,ra
> -    #	  14:   0c000000        jal     0<loongson_halt>
> -    #                    14: R_MIPS_26   _mcount
> -    #                    14: R_MIPS_NONE *ABS*
> -    #                    14: R_MIPS_NONE *ABS*
> -    #	 18:   00020021        nop
>       if ($is_module eq "0") {
>   	    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_26\\s+_mcount\$";
>       } else {
> -	    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
> +	    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_(HI16|26)\\s+_mcount\$";
>       }
>       $objdump .= " -Melf-trad".$endian."mips ";
>