On Wed, Sep 4, 2024 at 2:59 PM Sven Schnelle <svens@xxxxxxxxxxxxx> wrote:
>
> Add a function to decode argument types with the help of BTF. Will
> be used to display arguments in the function and function graph
> tracer.
>
> Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
> ---
> kernel/trace/trace_output.c | 68 +++++++++++++++++++++++++++++++++++++
> kernel/trace/trace_output.h | 9 +++++
> 2 files changed, 77 insertions(+)
>
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index d8b302d01083..70405c4cceb6 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -12,8 +12,11 @@
> #include <linux/sched/clock.h>
> #include <linux/sched/mm.h>
> #include <linux/idr.h>
> +#include <linux/btf.h>
> +#include <linux/bpf.h>
>
> #include "trace_output.h"
> +#include "trace_btf.h"
>
> /* must be a power of 2 */
> #define EVENT_HASHSIZE 128
> @@ -669,6 +672,71 @@ int trace_print_lat_context(struct trace_iterator *iter)
> return !trace_seq_has_overflowed(s);
> }
>
> +#ifdef CONFIG_FUNCTION_TRACE_ARGS
> +void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
> + unsigned long func)
> +{
> + const struct btf_param *param;
> + const struct btf_type *t;
> + const char *param_name;
> + char name[KSYM_NAME_LEN];
> + unsigned long arg;
> + struct btf *btf;
> + s32 tid, nr = 0;
> + int i;
> +
> + trace_seq_printf(s, "(");
> +
> + if (!ftrace_regs_has_args(fregs))
> + goto out;
> + if (lookup_symbol_name(func, name))
> + goto out;
> +
> + btf = bpf_get_btf_vmlinux();
> + if (IS_ERR_OR_NULL(btf))
> + goto out;
> +
> + t = btf_find_func_proto(name, &btf);
This is an excellent feature, and I am crafting a series of patches aimed
at enhancing the search performance for locating the btf by its name.
> + if (IS_ERR_OR_NULL(t))
> + goto out;
> +
> + param = btf_get_func_param(t, &nr);
> + if (!param)
> + goto out_put;
> +
> + for (i = 0; i < nr; i++) {
> + arg = ftrace_regs_get_argument(fregs, i);
> +
> + param_name = btf_name_by_offset(btf, param[i].name_off);
> + if (param_name)
> + trace_seq_printf(s, "%s = ", param_name);
> + t = btf_type_skip_modifiers(btf, param[i].type, &tid);
> + if (!t)
> + continue;
> + switch (BTF_INFO_KIND(t->info)) {
> + case BTF_KIND_PTR:
> + trace_seq_printf(s, "0x%lx", arg);
> + break;
> + case BTF_KIND_INT:
> + trace_seq_printf(s, "%ld", arg);
> + break;
> + case BTF_KIND_ENUM:
> + trace_seq_printf(s, "%ld", arg);
> + break;
> + default:
> + trace_seq_printf(s, "0x%lx (%d)", arg, BTF_INFO_KIND(param[i].type));
> + break;
> + }
> + if (i < nr - 1)
> + trace_seq_printf(s, ", ");
> + }
> +out_put:
> + btf_put(btf);
> +out:
> + trace_seq_printf(s, ")");
> +}
> +#endif
> +
> /**
> * ftrace_find_event - find a registered event
> * @type: the type of event to look for
> diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
> index dca40f1f1da4..a21d8ce606f7 100644
> --- a/kernel/trace/trace_output.h
> +++ b/kernel/trace/trace_output.h
> @@ -41,5 +41,14 @@ extern struct rw_semaphore trace_event_sem;
> #define SEQ_PUT_HEX_FIELD(s, x) \
> trace_seq_putmem_hex(s, &(x), sizeof(x))
>
> +#ifdef CONFIG_FUNCTION_TRACE_ARGS
> +void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
> + unsigned long func);
> +#else
> +static inline void print_function_args(struct trace_seq *s, struct ftrace_regs *fregs,
> + unsigned long func) {
> + trace_seq_puts(s, "()");
> +}
> +#endif
> #endif
>
> --
> 2.43.0
>
>
