[PATCH bpf] perf, bpf: Use subprog name when reporting subprog ksymbol

[PATCH bpf] perf, bpf: Use subprog name when reporting subprog ksymbol

[Hou Tao]

From: Hou Tao <houtao1@huawei.com>

Since commit bfea9a8574f3 ("bpf: Add name to struct bpf_ksym"), when
reporting subprog ksymbol to perf, prog name instead of subprog name is
used. The backtrace of bpf program with subprogs will be incorrect as
shown below:

  ffffffffc02deace bpf_prog_e44a3057dcb151f8_overwrite+0x66
  ffffffffc02de9f7 bpf_prog_e44a3057dcb151f8_overwrite+0x9f
  ffffffffa71d8d4e trace_call_bpf+0xce
  ffffffffa71c2938 perf_call_bpf_enter.isra.0+0x48

overwrite is the entry program and it invokes the overwrite_htab subprog
through bpf_loop, but in above backtrace, overwrite program just jumps
inside itself.

Fixing it by using subprog name when reporting subprog ksymbol. After
the fix, the output of perf script will be correct as shown below:

  ffffffffc031aad2 bpf_prog_37c0bec7d7c764a4_overwrite_htab+0x66
  ffffffffc031a9e7 bpf_prog_c7eb827ef4f23e71_overwrite+0x9f
  ffffffffa3dd8d4e trace_call_bpf+0xce
  ffffffffa3dc2938 perf_call_bpf_enter.isra.0+0x48

Fixes: bfea9a8574f3 ("bpf: Add name to struct bpf_ksym")
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4ec3717003d5..8b50ef2569d9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9030,7 +9030,7 @@ static void perf_event_bpf_emit_ksymbols(struct bpf_prog *prog,
 				PERF_RECORD_KSYMBOL_TYPE_BPF,
 				(u64)(unsigned long)subprog->bpf_func,
 				subprog->jited_len, unregister,
-				prog->aux->ksym.name);
+				subprog->aux->ksym.name);
 		}
 	}
 }
-- 
2.29.2

Re: [PATCH bpf] perf, bpf: Use subprog name when reporting subprog ksymbol

[Jiri Olsa]

On Mon, Nov 14, 2022 at 05:57:33PM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> Since commit bfea9a8574f3 ("bpf: Add name to struct bpf_ksym"), when
> reporting subprog ksymbol to perf, prog name instead of subprog name is
> used. The backtrace of bpf program with subprogs will be incorrect as
> shown below:
> 
>   ffffffffc02deace bpf_prog_e44a3057dcb151f8_overwrite+0x66
>   ffffffffc02de9f7 bpf_prog_e44a3057dcb151f8_overwrite+0x9f
>   ffffffffa71d8d4e trace_call_bpf+0xce
>   ffffffffa71c2938 perf_call_bpf_enter.isra.0+0x48
> 
> overwrite is the entry program and it invokes the overwrite_htab subprog
> through bpf_loop, but in above backtrace, overwrite program just jumps
> inside itself.
> 
> Fixing it by using subprog name when reporting subprog ksymbol. After
> the fix, the output of perf script will be correct as shown below:
> 
>   ffffffffc031aad2 bpf_prog_37c0bec7d7c764a4_overwrite_htab+0x66
>   ffffffffc031a9e7 bpf_prog_c7eb827ef4f23e71_overwrite+0x9f
>   ffffffffa3dd8d4e trace_call_bpf+0xce
>   ffffffffa3dc2938 perf_call_bpf_enter.isra.0+0x48
> 
> Fixes: bfea9a8574f3 ("bpf: Add name to struct bpf_ksym")
> Signed-off-by: Hou Tao <houtao1@huawei.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4ec3717003d5..8b50ef2569d9 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9030,7 +9030,7 @@ static void perf_event_bpf_emit_ksymbols(struct bpf_prog *prog,
>  				PERF_RECORD_KSYMBOL_TYPE_BPF,
>  				(u64)(unsigned long)subprog->bpf_func,
>  				subprog->jited_len, unregister,
> -				prog->aux->ksym.name);
> +				subprog->aux->ksym.name);
>  		}
>  	}
>  }
> -- 
> 2.29.2
> 

Re: [PATCH bpf] perf, bpf: Use subprog name when reporting subprog ksymbol

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Mon, 14 Nov 2022 17:57:33 +0800 you wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> Since commit bfea9a8574f3 ("bpf: Add name to struct bpf_ksym"), when
> reporting subprog ksymbol to perf, prog name instead of subprog name is
> used. The backtrace of bpf program with subprogs will be incorrect as
> shown below:
> 
> [...]

Here is the summary with links:
  - [bpf] perf, bpf: Use subprog name when reporting subprog ksymbol
    https://git.kernel.org/bpf/bpf/c/47df8a2f78bc

You are awesome, thank you!
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