On Mon, Oct 25, 2021 at 08:33:13AM +0000, Yafang Shao wrote:
> The hard-coded 16 is used in various bpf progs. These progs get task
> comm either via bpf_get_current_comm() or prctl() or
> bpf_core_read_str(), all of which can work well even if the task comm size
> is changed.
>
> In these BPF programs, one thing to be improved is the
> sched:sched_switch tracepoint args. As the tracepoint args are derived
> from the kernel, we'd better make it same with the kernel. So the macro
> TASK_COMM_LEN is converted to type enum, then all the BPF programs can
> get it through BTF.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> ---
> include/linux/sched.h | 9 +++++++--
> tools/testing/selftests/bpf/progs/test_stacktrace_map.c | 6 +++---
> tools/testing/selftests/bpf/progs/test_tracepoint.c | 6 +++---
> 3 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c1a927ddec64..124538db792c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -274,8 +274,13 @@ struct task_group;
>
> #define get_current_state() READ_ONCE(current->__state)
>
> -/* Task command name length: */
> -#define TASK_COMM_LEN 16
> +/*
> + * Define the task command name length as enum, then it can be visible to
> + * BPF programs.
> + */
> +enum {
> + TASK_COMM_LEN = 16,
> +};
>
> extern void scheduler_tick(void);
>
> diff --git a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> index 00ed48672620..e9b602a6dc1b 100644
> --- a/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> +++ b/tools/testing/selftests/bpf/progs/test_stacktrace_map.c
> @@ -1,7 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
> // Copyright (c) 2018 Facebook
>
> -#include <linux/bpf.h>
> +#include <vmlinux.h>
Why is this change needed here and below?
> #include <bpf/bpf_helpers.h>
>
> #ifndef PERF_MAX_STACK_DEPTH
> @@ -41,11 +41,11 @@ struct {
> /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
> struct sched_switch_args {
> unsigned long long pad;
> - char prev_comm[16];
> + char prev_comm[TASK_COMM_LEN];
> int prev_pid;
> int prev_prio;
> long long prev_state;
> - char next_comm[16];
> + char next_comm[TASK_COMM_LEN];
> int next_pid;
> int next_prio;
> };
> diff --git a/tools/testing/selftests/bpf/progs/test_tracepoint.c b/tools/testing/selftests/bpf/progs/test_tracepoint.c
> index 4b825ee122cf..f21982681e28 100644
> --- a/tools/testing/selftests/bpf/progs/test_tracepoint.c
> +++ b/tools/testing/selftests/bpf/progs/test_tracepoint.c
> @@ -1,17 +1,17 @@
> // SPDX-License-Identifier: GPL-2.0
> // Copyright (c) 2017 Facebook
>
> -#include <linux/bpf.h>
> +#include <vmlinux.h>
> #include <bpf/bpf_helpers.h>
>
> /* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
> struct sched_switch_args {
> unsigned long long pad;
> - char prev_comm[16];
> + char prev_comm[TASK_COMM_LEN];
> int prev_pid;
> int prev_prio;
> long long prev_state;
> - char next_comm[16];
> + char next_comm[TASK_COMM_LEN];
> int next_pid;
> int next_prio;
> };
> --
> 2.17.1
>
--
Kees Cook
