From: sdf@google.com
To: Xu Kuohai <xukuohai@huaweicloud.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
John Fastabend <john.fastabend@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
KP Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>
Subject: Re: [PATCH] libbpf: Avoid allocating reg_name with sscanf in parse_usdt_arg()
Date: Tue, 18 Oct 2022 11:32:46 -0700 [thread overview]
Message-ID: <Y07xTsStxyzZzxQZ@google.com> (raw)
In-Reply-To: <20221018145538.2046842-1-xukuohai@huaweicloud.com>
On 10/18, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@huawei.com>
> 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>
Addresses Andrii's suggestion from the following:
https://lore.kernel.org/bpf/86c88c01-22eb-b7f8-9c65-0faf97b4096b@huawei.com/
Acked-by: Stanislav Fomichev <sdf@google.com>
> ---
> tools/lib/bpf/usdt.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
> diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
> index 49f3c3b7f609..28fa1b2283de 100644
> --- a/tools/lib/bpf/usdt.c
> +++ b/tools/lib/bpf/usdt.c
> @@ -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)
> {
> - char *reg_name = NULL;
> + char reg_name[16];
> int arg_sz, len, reg_off;
> long off;
> - if (sscanf(arg_str, " %d @ %ld ( %%%m[^)] ) %n", &arg_sz, &off,
> ®_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) */
> 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 @ %%%ms %n", &arg_sz, ®_name, &len)
> == 2) {
> + } else if (sscanf(arg_str, " %d @ %%%15s %n", &arg_sz, reg_name, &len)
> == 2) {
> /* Register read case, e.g., -4@%eax */
> 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;
> @@ -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)
> {
> - char *reg_name = NULL;
> + char reg_name[16];
> int arg_sz, len, reg_off;
> long off;
> - if (sscanf(arg_str, " %d @ %ld ( %m[a-z0-9] ) %n", &arg_sz, &off,
> ®_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) */
> 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;
> @@ -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->val_off = off;
> arg->reg_off = 0;
> - } else if (sscanf(arg_str, " %d @ %m[a-z0-9] %n", &arg_sz, ®_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 */
> 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;
> --
> 2.30.2
next prev parent reply other threads:[~2022-10-18 18:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-18 14:55 [PATCH] libbpf: Avoid allocating reg_name with sscanf in parse_usdt_arg() Xu Kuohai
2022-10-18 18:32 ` sdf [this message]
2022-10-21 21:30 ` patchwork-bot+netdevbpf
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