On 9/2/22 12:56 AM, Jiri Olsa wrote:
On Wed, Aug 31, 2022 at 08:26:57AM -0700, Yonghong Song wrote:Now instead of the number of arguments, the number of registers holding argument values are stored in trampoline. Update the description of bpf_get_func_arg[_cnt]() helpers. Previous programs without struct arguments should continue to work as usual. Signed-off-by: Yonghong Song <yhs@xxxxxx> --- include/uapi/linux/bpf.h | 9 +++++---- tools/include/uapi/linux/bpf.h | 9 +++++---- 2 files changed, 10 insertions(+), 8 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 962960a98835..f9f43343ef93 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -5079,12 +5079,12 @@ union bpf_attr { * * long bpf_get_func_arg(void *ctx, u32 n, u64 *value) * Description - * Get **n**-th argument (zero based) of the traced function (for tracing programs) + * Get **n**-th argument register (zero based) of the traced function (for tracing programs)I'm bit worried about the confusion between args/regs we create with this, but I don't any have better idea how to solve this keeping extra stack values for nr_args and nr_regs and have new helpers to get reg values.. but then bpf_get_func_arg still does not return the full argument value.. also given that the struct args should be rare, I guess it's fine ;-)
You are right. Since an argument may takes two u64 space, the helper bpf_get_func_arg() might not return the *whole* argument any more. But it still returns a func arg, maybe just a partial func arg. So the 'n' here has a semantic change, instead of 'n'th argument, it becomes 'n'th argument register. To create new helpers probably not needed, so that is why I made the description change to the existing helper which maintains backward compatability too.
jirka* returned in **value**. * * Return * 0 on success. - * **-EINVAL** if n >= arguments count of traced function. + * **-EINVAL** if n >= argument register count of traced function. * * long bpf_get_func_ret(void *ctx, u64 *value) * Description @@ -5097,10 +5097,11 @@ union bpf_attr { * * long bpf_get_func_arg_cnt(void *ctx) * Description - * Get number of arguments of the traced function (for tracing programs). + * Get number of registers of the traced function (for tracing programs) where + * function arguments are stored in these registers. * * Return - * The number of arguments of the traced function. + * The number of argument registers of the traced function. * * int bpf_get_retval(void) * Description
[...]
