On Fri, Apr 8, 2022 at 3:53 PM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Parsing of USDT arguments is architecture-specific; on aarch64 it is
> relatively easy since registers used are x[0-31], sp. Format is
> slightly different compared to x86_64; forms are
>
> - "size @ [ reg[,offset] ]" for dereferences, for example
> "-8 @ [ sp, 76 ]" ; " -4 @ [ sp ]"
> - "size @ reg" for register values; for example
> "-4@x0"
> - "size @ value" for raw values; for example
> "-8@1"
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/lib/bpf/usdt.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index 0677bbd..6165d40 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
> @@ -1170,7 +1170,7 @@ static int parse_usdt_spec(struct usdt_spec *spec, const struct usdt_note *note,
>
> /* Architecture-specific logic for parsing USDT argument location specs */
>
> -#if defined(__x86_64__) || defined(__i386__) || defined(__s390x__)
> +#if defined(__x86_64__) || defined(__i386__) || defined(__s390x__) || defined(__aarch64__)
>
> static int init_usdt_arg_spec(struct usdt_arg_spec *arg, enum usdt_arg_type arg_type, int arg_sz,
> __u64 val_off, int reg_off)
> @@ -1316,6 +1316,54 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
> return len;
> }
>
> +#elif defined(__aarch64__)
> +
> +static int calc_pt_regs_off(const char *reg_name)
> +{
> + int reg_num;
> +
> + if (sscanf(reg_name, "x%d", ®_num) == 1) {
> + if (reg_num >= 0 && reg_num < 31)
> + return offsetof(struct user_pt_regs, regs[reg_num]);
> + } else if (strcmp(reg_name, "sp") == 0) {
> + return offsetof(struct user_pt_regs, sp);
> + }
> + pr_warn("usdt: unrecognized register '%s'\n", reg_name);
> + return -ENOENT;
> +}
> +
> +static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> +{
> + char *reg_name = NULL;
> + int arg_sz, len, ret;
> + long off = 0;
> +
> + if (sscanf(arg_str, " %d @ \[ %m[^,], %ld ] %n", &arg_sz, ®_name, &off, &len) == 3 ||
> + sscanf(arg_str, " %d @ \[ %m[a-z0-9] ] %n", &arg_sz, ®_name, &len) == 2) {
I'm not sure about the behavior here w.r.t. reg_name and memory
allocation. What if first sscanf() matches reg_name but fails at %ld,
will reg_name be allocated and then second sscanf() will reallocate
(and thus we'll have a memory leak).
We might have similar problems in other implementations, actually...
Either way, came here to ask to split two sscanfs into two separate
branches, so that we have a clear linear pattern. One sscanf, handle
it if successful, otherwise move on to next case.
Also a question about [a-z0-9] for register in one case and [^,] in
another. Should the first one be [a-z0-9] as well?
> + /* Memory dereference case, e.g., -4@[sp, 96], -4@[sp] */
> + ret = init_usdt_arg_spec(arg, USDT_ARG_REG_DEREF, arg_sz, off,
> + calc_pt_regs_off(reg_name));
> + free(reg_name);
> + } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
> + /* Constant value case, e.g., 4@5 */
> + ret = init_usdt_arg_spec(arg, USDT_ARG_CONST, arg_sz, off, 0);
> + } else if (sscanf(arg_str, " %d @ %ms %n", &arg_sz, ®_name, &len) == 2) {
> + /* Register read case, e.g., -8@x4 */
> + ret = init_usdt_arg_spec(arg, USDT_ARG_REG, arg_sz, 0, calc_pt_regs_off(reg_name));
> + free(reg_name);
> + } else {
> + pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
> + return -EINVAL;
> + }
> +
> + if (ret < 0) {
> + pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
> + arg_num, arg_str, arg_sz);
> + return ret;
> + }
> + return len;
> +}
> +
> #else
>
> static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
> --
> 1.8.3.1
>
