Re: [PATCH 4/5] tracing/probes: Extend max length of argument string
From: Google
Date: Sun Jul 12 2026 - 22:16:35 EST
On Mon, 13 Jul 2026 00:06:42 +0900
"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:
> From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>
> To support BTF argument parsing (such as accessing fields within nested
> structures via typecasting), the maximum argument string length needs
> to be extended. Extend MAX_ARGSTR_LEN from 63 to 256.
>
> Since MAX_ARGSTR_LEN was previously reused to format command heads in
> trace_*probe_match_command_head() functions, introduce a dedicated
> MAX_COMMON_HEAD_LEN (63) macro for matching command heads and switch
> these functions to use the new macro.
>
> Assisted-by: Antigravity:gemini-3.5-flash
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Sashiko asked to extend other macros,
> Does this code also need to increase MAX_BTF_ARGS_LEN and MAX_DENTRY_ARGS_LEN?
I don't agree this. MAX_BTF_ARGS_LEN is only for expanding "$args" into
each parameter names. The other arguments are kept on the same memory.
MAX_DENTRY_ARGS_LEN is already 256, so I think if that is too long,
it should be rejected.
(But MAX_ARGSTR_LEN should be 255.)
BTW, both macro names are a bit complicated because those are just
buffer size, not max length of something.
Thank you,
> ---
> kernel/trace/trace_fprobe.c | 2 +-
> kernel/trace/trace_kprobe.c | 2 +-
> kernel/trace/trace_probe.h | 3 ++-
> kernel/trace/trace_uprobe.c | 2 +-
> .../ftrace/test.d/dynevent/fprobe_syntax_errors.tc | 2 +-
> .../ftrace/test.d/dynevent/tprobe_syntax_errors.tc | 2 +-
> .../ftrace/test.d/kprobe/kprobe_syntax_errors.tc | 2 +-
> 7 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
> index 536781cd4c47..5638a90e61cc 100644
> --- a/kernel/trace/trace_fprobe.c
> +++ b/kernel/trace/trace_fprobe.c
> @@ -238,7 +238,7 @@ static bool trace_fprobe_is_busy(struct dyn_event *ev)
> static bool trace_fprobe_match_command_head(struct trace_fprobe *tf,
> int argc, const char **argv)
> {
> - char buf[MAX_ARGSTR_LEN + 1];
> + char buf[MAX_COMMON_HEAD_LEN + 1];
>
> if (!argc)
> return true;
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index cfa807d8e760..cc24e992732c 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -149,7 +149,7 @@ static bool trace_kprobe_is_busy(struct dyn_event *ev)
> static bool trace_kprobe_match_command_head(struct trace_kprobe *tk,
> int argc, const char **argv)
> {
> - char buf[MAX_ARGSTR_LEN + 1];
> + char buf[MAX_COMMON_HEAD_LEN + 1];
>
> if (!argc)
> return true;
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index e64e323244a5..e6aee800a7d9 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -32,7 +32,8 @@
> #include "trace_output.h"
>
> #define MAX_TRACE_ARGS 128
> -#define MAX_ARGSTR_LEN 63
> +#define MAX_ARGSTR_LEN 256
> +#define MAX_COMMON_HEAD_LEN 63
> #define MAX_ARRAY_LEN 64
> #define MAX_ARG_NAME_LEN 32
> #define MAX_BTF_ARGS_LEN 128
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index b2e264a4b96c..67bd8fd91e3e 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -281,7 +281,7 @@ static bool trace_uprobe_is_busy(struct dyn_event *ev)
> static bool trace_uprobe_match_command_head(struct trace_uprobe *tu,
> int argc, const char **argv)
> {
> - char buf[MAX_ARGSTR_LEN + 1];
> + char buf[MAX_COMMON_HEAD_LEN + 1];
> int len;
>
> if (!argc)
> diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
> index e9d7e6919c7f..984ab94df213 100644
> --- a/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
> +++ b/tools/testing/selftests/ftrace/test.d/dynevent/fprobe_syntax_errors.tc
> @@ -75,7 +75,7 @@ check_error 'f vfs_read ^arg123456789012345678901234567890=@11' # ARG_NAME_TOO_L
> check_error 'f vfs_read ^=@11' # NO_ARG_NAME
> check_error 'f vfs_read ^var.1=@11' # BAD_ARG_NAME
> check_error 'f vfs_read var1=@11 ^var1=@12' # USED_ARG_NAME
> -check_error 'f vfs_read ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))' # ARG_TOO_LONG
> +check_error 'f vfs_read ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))))))))))))))))))))))' # ARG_TOO_LONG
> check_error 'f vfs_read arg1=^' # NO_ARG_BODY
>
>
> diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/tprobe_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/dynevent/tprobe_syntax_errors.tc
> index ffe8ffef4027..2d0905b2c8b7 100644
> --- a/tools/testing/selftests/ftrace/test.d/dynevent/tprobe_syntax_errors.tc
> +++ b/tools/testing/selftests/ftrace/test.d/dynevent/tprobe_syntax_errors.tc
> @@ -61,7 +61,7 @@ check_error 't kfree ^arg123456789012345678901234567890=@11' # ARG_NAME_TOO_LOG
> check_error 't kfree ^=@11' # NO_ARG_NAME
> check_error 't kfree ^var.1=@11' # BAD_ARG_NAME
> check_error 't kfree var1=@11 ^var1=@12' # USED_ARG_NAME
> -check_error 't kfree ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))' # ARG_TOO_LONG
> +check_error 't kfree ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))))))))))))))))))))))' # ARG_TOO_LONG
> check_error 't kfree arg1=^' # NO_ARG_BODY
>
>
> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
> index 21ce8414459f..d28f63b7e8a9 100644
> --- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
> +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_syntax_errors.tc
> @@ -71,7 +71,7 @@ check_error 'p vfs_read ^arg123456789012345678901234567890=@11' # ARG_NAME_TOO_L
> check_error 'p vfs_read ^=@11' # NO_ARG_NAME
> check_error 'p vfs_read ^var.1=@11' # BAD_ARG_NAME
> check_error 'p vfs_read var1=@11 ^var1=@12' # USED_ARG_NAME
> -check_error 'p vfs_read ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))' # ARG_TOO_LONG
> +check_error 'p vfs_read ^+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(+1234567(@1234))))))))))))))))))))))))))' # ARG_TOO_LONG
> check_error 'p vfs_read arg1=^' # NO_ARG_BODY
>
> # instruction boundary check is valid on x86 (at this moment)
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>