On Mon, Dec 20, 2021 at 9:53 PM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote:
>
> Add syscall-specific variants of BPF_KPROBE/BPF_KRETPROBE named
> BPF_KPROBE_SYSCALL/BPF_KRETPROBE_SYSCALL ([0]). These new macros
> hide the underlying way of getting syscall input arguments and
> return values. With these new macros, the following code:
>
> SEC("kprobe/__x64_sys_close")
> int BPF_KPROBE(do_sys_close, struct pt_regs *regs)
> {
> int fd;
>
> fd = PT_REGS_PARM1_CORE(regs);
> /* do something with fd */
> }
>
> can be written as:
>
> SEC("kprobe/__x64_sys_close")
> int BPF_KPROBE_SYSCALL(do_sys_close, int fd)
> {
> /* do something with fd */
> }
>
> [0] Closes: https://github.com/libbpf/libbpf/issues/425
>
> Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
> ---
As Yonghong mentioned, let's wait for PT_REGS_PARMx_SYSCALL macros to
land and use those (due to 4th argument quirkiness on x86 arches).
> tools/lib/bpf/bpf_tracing.h | 45 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> index db05a5937105..eb4b567e443f 100644
> --- a/tools/lib/bpf/bpf_tracing.h
> +++ b/tools/lib/bpf/bpf_tracing.h
> @@ -489,4 +489,49 @@ typeof(name(0)) name(struct pt_regs *ctx) \
> } \
> static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
>
> +#define ___bpf_syscall_args0() ctx, regs
> +#define ___bpf_syscall_args1(x) \
> + ___bpf_syscall_args0(), (void *)PT_REGS_PARM1_CORE(regs)
> +#define ___bpf_syscall_args2(x, args...) \
> + ___bpf_syscall_args1(args), (void *)PT_REGS_PARM2_CORE(regs)
> +#define ___bpf_syscall_args3(x, args...) \
> + ___bpf_syscall_args2(args), (void *)PT_REGS_PARM3_CORE(regs)
> +#define ___bpf_syscall_args4(x, args...) \
> + ___bpf_syscall_args3(args), (void *)PT_REGS_PARM4_CORE(regs)
> +#define ___bpf_syscall_args5(x, args...) \
> + ___bpf_syscall_args4(args), (void *)PT_REGS_PARM5_CORE(regs)
> +#define ___bpf_syscall_args(args...) \
> + ___bpf_apply(___bpf_syscall_args, ___bpf_narg(args))(args)
try keeping each definition on a single line, make them much more
readable and I think still fits in 100 character limit
> +
> +/*
> + * BPF_KPROBE_SYSCALL is a variant of BPF_KPROBE, which is intended for
> + * tracing syscall functions. It hides the underlying platform-specific
let's add a simple example to explain what kind of tracing syscall
functions we mean.
"tracing syscall functions, like __x64_sys_close." ?
> + * low-level way of getting syscall input arguments from struct pt_regs, and
> + * provides a familiar typed and named function arguments syntax and
> + * semantics of accessing syscall input paremeters.
typo: parameters
> + *
> + * Original struct pt_regs* context is preserved as 'ctx' argument. This might
> + * be necessary when using BPF helpers like bpf_perf_event_output().
> + */
> +#define BPF_KPROBE_SYSCALL(name, args...) \
> +name(struct pt_regs *ctx); \
> +static __attribute__((always_inline)) typeof(name(0)) \
> +____##name(struct pt_regs *ctx, struct pt_regs *regs, ##args); \
> +typeof(name(0)) name(struct pt_regs *ctx) \
> +{ \
> + _Pragma("GCC diagnostic push") \
> + _Pragma("GCC diagnostic ignored \"-Wint-conversion\"") \
> + struct pt_regs *regs = PT_REGS_PARM1(ctx); \
please move it out of _Pragma region, no need to guard it
> + return ____##name(___bpf_syscall_args(args)); \
> + _Pragma("GCC diagnostic pop") \
> +} \
> +static __attribute__((always_inline)) typeof(name(0)) \
> +____##name(struct pt_regs *ctx, struct pt_regs *regs, ##args)
I don't think we need to add another magical hidden argument "regs".
Anyone who will need it for something can get it from the hidden ctx
with PT_REGS_PARM1(ctx) anyways.
> +
> +/*
> + * BPF_KRETPROBE_SYSCALL is just an alias to BPF_KRETPROBE,
> + * it provides optional return value (in addition to `struct pt_regs *ctx`)
> + */
> +#define BPF_KRETPROBE_SYSCALL BPF_KRETPROBE
> +
hm... do we even need BPF_KRETPROBE_SYSCALL then? Let's drop it, it
doesn't provide much value, just creates a confusion.
> #endif
> --
> 2.30.2
