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libbpf: USDT arm arg parsing support 

Parsing of USDT arguments is architecture-specific; on arm it is
relatively easy since registers used are r[0-10], fp, ip, sp, lr,
pc. Format is slightly different compared to aarch64; forms are

- "size @ [ reg, #offset ]" for dereferences, for example
  "-8 @ [ sp, #76 ]" ; " -4 @ [ sp ]"
- "size @ reg" for register values; for example
  "-4@r0"
- "size @ #value" for raw values; for example
  "-8@#1"

Add support for parsing USDT arguments for ARM architecture.

To test the above changes QEMU's virt[1] board with cortex-a15
CPU was used. libbpf-bootstrap's usdt example[2] was modified to attach
to a test program with DTRACE_PROBE1/2/3/4... probes to test different
combinations.

[1] https://www.qemu.org/docs/master/system/arm/virt.html
[2] https://github.com/libbpf/libbpf-bootstrap/blob/master/examples/c/usdt.bpf.c

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230307120440.25941-3-puranjay12@gmail.com
This commit is contained in:
Puranjay Mohan 2023-03-07 12:04:40 +00:00 committed by Andrii Nakryiko
parent 98e678e9bc
commit 720d93b60a
1 changed files with 80 additions and 0 deletions
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80
tools/lib/bpf/usdt.c
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@ -1465,6 +1465,86 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
return len;
}
#elif defined(__arm__)
static int calc_pt_regs_off(const char *reg_name)
{
static struct {
const char *name;
size_t pt_regs_off;
} reg_map[] = {
{ "r0", offsetof(struct pt_regs, uregs[0]) },
{ "r1", offsetof(struct pt_regs, uregs[1]) },
{ "r2", offsetof(struct pt_regs, uregs[2]) },
{ "r3", offsetof(struct pt_regs, uregs[3]) },
{ "r4", offsetof(struct pt_regs, uregs[4]) },
{ "r5", offsetof(struct pt_regs, uregs[5]) },
{ "r6", offsetof(struct pt_regs, uregs[6]) },
{ "r7", offsetof(struct pt_regs, uregs[7]) },
{ "r8", offsetof(struct pt_regs, uregs[8]) },
{ "r9", offsetof(struct pt_regs, uregs[9]) },
{ "r10", offsetof(struct pt_regs, uregs[10]) },
{ "fp", offsetof(struct pt_regs, uregs[11]) },
{ "ip", offsetof(struct pt_regs, uregs[12]) },
{ "sp", offsetof(struct pt_regs, uregs[13]) },
{ "lr", offsetof(struct pt_regs, uregs[14]) },
{ "pc", offsetof(struct pt_regs, uregs[15]) },
};
int i;
for (i = 0; i < ARRAY_SIZE(reg_map); i++) {
if (strcmp(reg_name, reg_map[i].name) == 0)
return reg_map[i].pt_regs_off;
}
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, int *arg_sz)
{
char reg_name[16];
int len, reg_off;
long off;
if (sscanf(arg_str, " %d @ \[ %15[a-z0-9] , #%ld ] %n",
arg_sz, reg_name, &off, &len) == 3) {
/* Memory dereference case, e.g., -4@[fp, #96] */
arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name);
if (reg_off < 0)
return reg_off;
arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ \[ %15[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);
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 @ %15[a-z0-9] %n", arg_sz, reg_name, &len) == 2) {
/* Register read case, e.g., -8@r4 */
arg->arg_type = USDT_ARG_REG;
arg->val_off = 0;
reg_off = calc_pt_regs_off(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;
}
return len;
}
#else
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg, int *arg_sz)