Re: [PATCH 2/2] perf trace: Increase TRACE_AUG_MAX_BUF to 128 and document beauty_map encoding

[Aaron Tomlin]

On Thu, Oct 01, 2026 at 11:54:40PM -0700, Ian Rogers wrote:
> With sockaddr arguments copied as buffers via beauty_map_enter, the
> 32-byte TRACE_AUG_MAX_BUF limit only held 2 bytes of sa_family plus 30
> bytes of AF_LOCAL sun_path, truncating longer socket paths such as
> "/var/run/.heim_org.h5l.kcm-socket".
> 
> Since struct augmented_arg already reserves PATH_MAX (4096) bytes,
> increase TRACE_AUG_MAX_BUF to 128 (SS_MAXSIZE, the size of struct
> sockaddr_storage), which covers all 110 bytes of struct sockaddr_un
> without changing map sizes. Also document the 1-based negative
> -(arg_idx + 1) encoding used in beauty_array for paired length
> arguments.
> 
> Suggested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Assisted-by: Antigravity:gemini-3.1-pro
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/builtin-trace.c                            | 8 +++++++-
>  tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c | 8 ++++----
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index c34c9f129836..4094141461f9 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -4174,7 +4174,12 @@ static int trace__bpf_sys_enter_beauty_map(struct trace *trace, int e_machine, i
>  				continue;
>  
>  			bt = sc->arg_fmt[i].type;
> -			/* Copy a sockaddr as a buffer sized by the next argument, e.g. addrlen. */
> +			/*
> +			 * Copy a sockaddr as a buffer sized by the next
> +			 * argument (i + 1), e.g. addrlen. A negative entry
> +			 * -(j + 1) encodes the 0-based length argument index j
> +			 * as 1-based so arg 0 is -1 rather than 0.
> +			 */
>  			if (strcmp(name, "sockaddr") == 0 && field->next &&
>  			    strstr(field->next->name, "len"))
>  				beauty_array[i] = -((i + 1) + 1);
> @@ -4210,6 +4215,7 @@ static int trace__bpf_sys_enter_beauty_map(struct trace *trace, int e_machine, i
>  				     strstr(field_tmp->name, "siz") ||  /* size, bufsiz */
>  				     (strstr(field_tmp->name, "len") && strcmp(field_tmp->name, "filename")))) {
>  					 /* filename's got 'len' in it, we don't want that */
> +					/* 1-based negative index of length arg j. */
>  					beauty_array[i] = -(j + 1);
>  					can_augment = true;
>  					break;
> diff --git a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> index 0b2ef9541f84..28ebb9a72776 100644
> --- a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> @@ -28,7 +28,7 @@
>  
>  #define MAX_CPUS  4096
>  
> -#define TRACE_AUG_MAX_BUF 32 /* for buffer augmentation in perf trace */
> +#define TRACE_AUG_MAX_BUF 128 /* for buffer augmentation in perf trace */
>  
>  /* bpf-output associated map */
>  struct __augmented_syscalls__ {
> @@ -514,9 +514,9 @@ u64 ZERO = 0;
>   * value in the beauty_map. This is the relation of parameter type and its corresponding
>   * value in the beauty map, and how many bytes we read eventually:
>   *
> - * string: 1			      -> size of string
> - * struct: size of struct	      -> size of struct
> - * buffer: -1 * (index of paired len) -> value of paired len (maximum: TRACE_AUG_MAX_BUF)
> + * string: 1			          -> size of string
> + * struct: size of struct	          -> size of struct
> + * buffer: -(0-based index of paired len + 1) -> value of paired len (maximum: TRACE_AUG_MAX_BUF)
>   */
>  static inline int augment_arg(struct syscall_enter_args *args, int i,
>  			      unsigned int *beauty_map,
> -- 
> 2.56.0.rc1.315.gc6ed9934b7-goog
> 

Reviewed-by: Aaron Tomlin <atomlin@xxxxxxxxxxx>

-- 
Aaron Tomlin