libbpf: Usdt aarch64 arg parsing support

Parsing of USDT arguments is architecture-specific. On aarch64 it is
relatively easy since registers used are x[0-31] and sp. Format is
slightly different compared to x86_64. Possible forms are:

- "size@[reg[,offset]]" for dereferences, e.g. "-8@[sp,76]" and "-4@[sp]";
- "size@reg" for register values, e.g. "-4@x0";
- "size@value" for raw values, e.g. "-8@1".

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1649690496-1902-2-git-send-email-alan.maguire@oracle.com

diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index acf2d99..934c253 100644 (file)
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -1324,6 +1324,82 @@ 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", &reg_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, reg_off;
+       long off;
+
+       if (sscanf(arg_str, " %d @ \[ %m[a-z0-9], %ld ] %n", &arg_sz, &reg_name, &off, &len) == 3) {
+               /* Memory dereference case, e.g., -4@[sp, 96] */
+               arg->arg_type = USDT_ARG_REG_DEREF;
+               arg->val_off = off;
+               reg_off = calc_pt_regs_off(reg_name);
+               free(reg_name);
+               if (reg_off < 0)
+                       return reg_off;
+               arg->reg_off = reg_off;
+       } else if (sscanf(arg_str, " %d @ \[ %m[a-z0-9] ] %n", &arg_sz, &reg_name, &len) == 2) {
+               /* Memory dereference case, e.g., -4@[sp] */
+               arg->arg_type = USDT_ARG_REG_DEREF;
+               arg->val_off = 0;
+               reg_off = calc_pt_regs_off(reg_name);
+               free(reg_name);
+               if (reg_off < 0)
+                       return reg_off;
+               arg->reg_off = reg_off;
+       } else if (sscanf(arg_str, " %d @ %ld %n", &arg_sz, &off, &len) == 2) {
+               /* Constant value case, e.g., 4@5 */
+               arg->arg_type = USDT_ARG_CONST;
+               arg->val_off = off;
+               arg->reg_off = 0;
+       } else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) {
+               /* Register read case, e.g., -8@x4 */
+               arg->arg_type = USDT_ARG_REG;
+               arg->val_off = 0;
+               reg_off = calc_pt_regs_off(reg_name);
+               free(reg_name);
+               if (reg_off < 0)
+                       return reg_off;
+               arg->reg_off = reg_off;
+       } else {
+               pr_warn("usdt: unrecognized arg #%d spec '%s'\n", arg_num, arg_str);
+               return -EINVAL;
+       }
+
+       arg->arg_signed = arg_sz < 0;
+       if (arg_sz < 0)
+               arg_sz = -arg_sz;
+
+       switch (arg_sz) {
+       case 1: case 2: case 4: case 8:
+               arg->arg_bitshift = 64 - arg_sz * 8;
+               break;
+       default:
+               pr_warn("usdt: unsupported arg #%d (spec '%s') size: %d\n",
+                       arg_num, arg_str, arg_sz);
+               return -EINVAL;
+       }
+
+       return len;
+}
+
 #else
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)