[PATCH bpf-next] libbpf: Support riscv USDT argument parsing logic

[Andrii Nakryiko]

On Sun, Apr 17, 2022 at 8:53 PM Pu Lehui <pulehui at huawei.com> wrote:
>
> Add riscv-specific USDT argument specification parsing logic.
> riscv USDT argument format is shown below:
> - Memory dereference case:
>   "size at off(reg)", e.g. "-8 at -88(s0)"
> - Constant value case:
>   "size at val", e.g. "4 at 5"
> - Register read case:
>   "size at reg", e.g. "-8 at a1"
>
> s8 will be marked as poison while it's a reg of riscv, we need
> to alias it in advance.
>
> Signed-off-by: Pu Lehui <pulehui at huawei.com>
> ---

Can you please mention briefly the testing you performed as I'm not
able to test this locally.

>  tools/lib/bpf/usdt.c | 107 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 107 insertions(+)
>
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index 934c25301ac1..b8af409cc763 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
> @@ -10,6 +10,11 @@
>  #include <linux/ptrace.h>
>  #include <linux/kernel.h>
>
> +/* s8 will be marked as poison while it's a reg of riscv */
> +#if defined(__riscv)
> +#define rv_s8 s8
> +#endif
> +
>  #include "bpf.h"
>  #include "libbpf.h"
>  #include "libbpf_common.h"
> @@ -1400,6 +1405,108 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
>         return len;
>  }
>
> +#elif defined(__riscv)
> +
> +static int calc_pt_regs_off(const char *reg_name)
> +{
> +       static struct {
> +               const char *name;
> +               size_t pt_regs_off;
> +       } reg_map[] = {
> +               { "ra", offsetof(struct user_regs_struct, ra) },
> +               { "sp", offsetof(struct user_regs_struct, sp) },
> +               { "gp", offsetof(struct user_regs_struct, gp) },
> +               { "tp", offsetof(struct user_regs_struct, tp) },
> +               { "t0", offsetof(struct user_regs_struct, t0) },
> +               { "t1", offsetof(struct user_regs_struct, t1) },
> +               { "t2", offsetof(struct user_regs_struct, t2) },
> +               { "s0", offsetof(struct user_regs_struct, s0) },
> +               { "s1", offsetof(struct user_regs_struct, s1) },
> +               { "a0", offsetof(struct user_regs_struct, a0) },
> +               { "a1", offsetof(struct user_regs_struct, a1) },
> +               { "a2", offsetof(struct user_regs_struct, a2) },
> +               { "a3", offsetof(struct user_regs_struct, a3) },
> +               { "a4", offsetof(struct user_regs_struct, a4) },
> +               { "a5", offsetof(struct user_regs_struct, a5) },
> +               { "a6", offsetof(struct user_regs_struct, a6) },
> +               { "a7", offsetof(struct user_regs_struct, a7) },
> +               { "s2", offsetof(struct user_regs_struct, s2) },
> +               { "s3", offsetof(struct user_regs_struct, s3) },
> +               { "s4", offsetof(struct user_regs_struct, s4) },
> +               { "s5", offsetof(struct user_regs_struct, s5) },
> +               { "s6", offsetof(struct user_regs_struct, s6) },
> +               { "s7", offsetof(struct user_regs_struct, s7) },
> +               { "s8", offsetof(struct user_regs_struct, rv_s8) },
> +               { "s9", offsetof(struct user_regs_struct, s9) },
> +               { "s10", offsetof(struct user_regs_struct, s10) },
> +               { "s11", offsetof(struct user_regs_struct, s11) },
> +               { "t3", offsetof(struct user_regs_struct, t3) },
> +               { "t4", offsetof(struct user_regs_struct, t4) },
> +               { "t5", offsetof(struct user_regs_struct, t5) },
> +               { "t6", offsetof(struct user_regs_struct, t6) },

would it make sense to order registers a bit more "logically"? Like
s0-s11, t0-t6, etc. Right now it looks very random and it's hard to
see if all the registers from some range of registers are defined.

> +       };
> +       int i;
> +

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