Subject: Re: [PATCH v8 2/3] perf annotate: Support jump instruction with target as second operand

From: Ravi Bangoria <[email-masked]>
Date: Tue, 6 Dec 2016 11:38:28 +0530

Hi Arnaldo,

Hmm, so it's difficult to find example of this when we use debuginfo.
Because...

Jump__parse tries to look for two things 'offset' and 'target address'.

objdump with debuginfo will include offset in assembly f.e. annotate of
'smp_call_function_single' with perf.data and vmlinux I shared.

       │c00000000016d6ac:   cmpwi  cr7,r9,0                                                    ▒
       │c00000000016d6b0: ↑ bne    cr7,c00000000016d59c <.smp_call_function_single+0x8c>       ▒
       │c00000000016d6b4:   addis  r10,r2,-15                                                  ▒

objdump of same function with kcore.

       │c00000000016d6ac:   cmpwi  cr7,r9,0                                                    ▒
       │c00000000016d6b0: ↓ bne    cr7,0xc00000000016d59c                                      ▒
       │c00000000016d6b4:   addis  r10,r2,-15                                                  ▒

Annotating in first case won't show any issue because we directly get
offset. But in this case as well, we are parsing wrong target address
in ops->target.addr

While we don't have offset in second case, we use target address to
find it. And thus it shows wrong o/p something like:

       │       cmpwi  cr7,r9,0                                                                 ▒
       │     ↓ bne    3fffffffffe92afc                                                         ▒
       │       addis  r10,r2,-15                                                               ▒

BTW, we have lot of such instructions in kernel.

Thanks,
-Ravi

On Monday 05 December 2016 09:26 PM, Ravi Bangoria wrote:
> Arch like powerpc has jump instructions that includes target address
> as second operand. For example, 'bne  cr7,0xc0000000000f6154'. Add
> support for such instruction in perf annotate.
>
> objdump o/p:
>   c0000000000f6140:   ld     r9,1032(r31)
>   c0000000000f6144:   cmpdi  cr7,r9,0
>   c0000000000f6148:   bne    cr7,0xc0000000000f6154
>   c0000000000f614c:   ld     r9,2312(r30)
>   c0000000000f6150:   std    r9,1032(r31)
>   c0000000000f6154:   ld     r9,88(r31)
>
> Corresponding perf annotate o/p:
>
> Before patch:
>          ld     r9,1032(r31)
>          cmpdi  cr7,r9,0
>       v  bne    3ffffffffff09f2c
>          ld     r9,2312(r30)
>          std    r9,1032(r31)
>   74:    ld     r9,88(r31)
>
> After patch:
>          ld     r9,1032(r31)
>          cmpdi  cr7,r9,0
>       v  bne    74
>          ld     r9,2312(r30)
>          std    r9,1032(r31)
>   74:    ld     r9,88(r31)
>
> Signed-off-by: Ravi Bangoria <[email-masked]>
> ---
> Changes in v8:
>   - v7: https://lkml.org/lkml/2016/9/21/436
>   - Rebase to acme/perf/core
>   - Little change in patch description.
>   - No logical changes. (Cross arch annotate patches are in. This patch
>     is for hardening annotate for powerpc.)
>
>  tools/perf/util/annotate.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index ea7e0de..590244e 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -223,8 +223,12 @@ bool ins__is_call(const struct ins *ins)
>  static int jump__parse(struct arch *arch __maybe_unused, struct ins_operands *ops, struct map *map __maybe_unused)
>  {
>  	const char *s = strchr(ops->raw, '+');
> +	const char *c = strchr(ops->raw, ',');
>
> -	ops->target.addr = strtoull(ops->raw, NULL, 16);
> +	if (c++ != NULL)
> +		ops->target.addr = strtoull(c, NULL, 16);
> +	else
> +		ops->target.addr = strtoull(ops->raw, NULL, 16);
>
>  	if (s++ != NULL)
>  		ops->target.offset = strtoull(s, NULL, 16);