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libbpf: Avoid allocating reg_name with sscanf in parse_usdt_arg()

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The reg_name in parse_usdt_arg() is used to hold register name, which
is short enough to be held in a 16-byte array, so we could define
reg_name as char reg_name[16] to avoid dynamically allocating reg_name
with sscanf.

Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20221018145538.2046842-1-xukuohai@huaweicloud.com
This commit is contained in:
Xu Kuohai
2022-10-18 10:55:38 -04:00
committed by Andrii Nakryiko
parent 3cd45b660c
commit 1bb7a8349a
1 changed files with 6 additions and 10 deletions
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16
src/usdt.c
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@@ -1225,26 +1225,24 @@ static int calc_pt_regs_off(const char *reg_name)
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg) static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{ {
char *reg_name = NULL; char reg_name[16];
int arg_sz, len, reg_off; int arg_sz, len, reg_off;
long off; long off;
if (sscanf(arg_str, " %d @ %ld ( %%%m[^)] ) %n", &arg_sz, &off, &reg_name, &len) == 3) { if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n", &arg_sz, &off, reg_name, &len) == 3) {
/* Memory dereference case, e.g., -4@-20(%rbp) */ /* Memory dereference case, e.g., -4@-20(%rbp) */
arg->arg_type = USDT_ARG_REG_DEREF; arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off; arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name); reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0) if (reg_off < 0)
return reg_off; return reg_off;
arg->reg_off = reg_off; arg->reg_off = reg_off;
} else if (sscanf(arg_str, " %d @ %%%ms %n", &arg_sz, &reg_name, &len) == 2) { } else if (sscanf(arg_str, " %d @ %%%15s %n", &arg_sz, reg_name, &len) == 2) {
/* Register read case, e.g., -4@%eax */ /* Register read case, e.g., -4@%eax */
arg->arg_type = USDT_ARG_REG; arg->arg_type = USDT_ARG_REG;
arg->val_off = 0; arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name); reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0) if (reg_off < 0)
return reg_off; return reg_off;
arg->reg_off = reg_off; arg->reg_off = reg_off;
@@ -1456,16 +1454,15 @@ static int calc_pt_regs_off(const char *reg_name)
static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg) static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg)
{ {
char *reg_name = NULL; char reg_name[16];
int arg_sz, len, reg_off; int arg_sz, len, reg_off;
long off; long off;
if (sscanf(arg_str, " %d @ %ld ( %m[a-z0-9] ) %n", &arg_sz, &off, &reg_name, &len) == 3) { if (sscanf(arg_str, " %d @ %ld ( %15[a-z0-9] ) %n", &arg_sz, &off, reg_name, &len) == 3) {
/* Memory dereference case, e.g., -8@-88(s0) */ /* Memory dereference case, e.g., -8@-88(s0) */
arg->arg_type = USDT_ARG_REG_DEREF; arg->arg_type = USDT_ARG_REG_DEREF;
arg->val_off = off; arg->val_off = off;
reg_off = calc_pt_regs_off(reg_name); reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0) if (reg_off < 0)
return reg_off; return reg_off;
arg->reg_off = reg_off; arg->reg_off = reg_off;
@@ -1474,12 +1471,11 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
arg->arg_type = USDT_ARG_CONST; arg->arg_type = USDT_ARG_CONST;
arg->val_off = off; arg->val_off = off;
arg->reg_off = 0; arg->reg_off = 0;
} else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, &reg_name, &len) == 2) { } else if (sscanf(arg_str, " %d @ %15[a-z0-9] %n", &arg_sz, reg_name, &len) == 2) {
/* Register read case, e.g., -8@a1 */ /* Register read case, e.g., -8@a1 */
arg->arg_type = USDT_ARG_REG; arg->arg_type = USDT_ARG_REG;
arg->val_off = 0; arg->val_off = 0;
reg_off = calc_pt_regs_off(reg_name); reg_off = calc_pt_regs_off(reg_name);
free(reg_name);
if (reg_off < 0) if (reg_off < 0)
return reg_off; return reg_off;
arg->reg_off = reg_off; arg->reg_off = reg_off;