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Message-ID: <CAEf4BzZuz5NVzDa=srfvuMtMg6Jmy85bAaBkgSXiz8h2aTQ9Hw@mail.gmail.com>
Date: Tue, 5 Apr 2022 17:06:30 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Alan Maguire <alan.maguire@...cle.com>
Cc: Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>, Martin Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
john fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] libbpf: improve string handling for uprobe
name-based attach
On Tue, Apr 5, 2022 at 2:46 PM Alan Maguire <alan.maguire@...cle.com> wrote:
>
> For uprobe attach, libraries are identified by matching a ".so"
> substring in the binary path. This matches a lot of patterns that do
> not conform to library .so[.version] suffixes, so instead match a ".so"
> _suffix_, and if that fails match a ".so." substring for the versioned
> library case.
>
You are making two separate changes in one patch, let's split them.
> For uprobe auto-attach, the parsing can be simplified for the SEC()
> name to a single ssscanf(); the return value of the sscanf can then
too many sss :)
> be used to distinguish between sections that simply specify
> "u[ret]probe" (and thus cannot auto-attach), those that specify
> "u[ret]probe/binary_path:function+offset" etc.
>
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---
> tools/lib/bpf/libbpf.c | 77 ++++++++++++++++-------------------------
> tools/lib/bpf/libbpf_internal.h | 5 +++
> 2 files changed, 35 insertions(+), 47 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 91ce94b..3f23e88 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10750,7 +10750,7 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
> const char *search_paths[3] = {};
> int i;
>
> - if (strstr(file, ".so")) {
> + if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
> search_paths[0] = getenv("LD_LIBRARY_PATH");
> search_paths[1] = "/usr/lib64:/usr/lib";
> search_paths[2] = arch_specific_lib_paths();
> @@ -10897,60 +10897,43 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
> static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
> {
> DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
> - char *func, *probe_name, *func_end;
> - char *func_name, binary_path[512];
> - unsigned long long raw_offset;
> + char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
> + int n, ret = -EINVAL;
> size_t offset = 0;
> - int n;
>
> *link = NULL;
>
> - opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
> - if (opts.retprobe)
> - probe_name = prog->sec_name + sizeof("uretprobe") - 1;
> - else
> - probe_name = prog->sec_name + sizeof("uprobe") - 1;
> - if (probe_name[0] == '/')
> - probe_name++;
> -
> - /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
> - if (strlen(probe_name) == 0)
> - return 0;
> -
> - snprintf(binary_path, sizeof(binary_path), "%s", probe_name);
> - /* ':' should be prior to function+offset */
> - func_name = strrchr(binary_path, ':');
> - if (!func_name) {
> + n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[a-zA-Z0-9_.]+%zu",
note that previously you were using %li for offset which allows
decimal and hexadecimal formats, I think that's convenient, let's
allow that still
> + &probe_type, &binary_path, &func_name, &offset);
> + switch (n) {
> + case 1:
> + /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
> + ret = 0;
> + break;
> + case 2:
> pr_warn("section '%s' missing ':function[+offset]' specification\n",
> prog->sec_name);
please use 'prog '%s': ' prefix in these attach_xxx() functions for consistency
> - return -EINVAL;
> - }
> - func_name[0] = '\0';
> - func_name++;
> - n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
> - if (n < 1) {
> - pr_warn("uprobe name '%s' is invalid\n", func_name);
> - return -EINVAL;
> - }
> - if (opts.retprobe && offset != 0) {
> - free(func);
> - pr_warn("uretprobes do not support offset specification\n");
> - return -EINVAL;
> - }
> -
> - /* Is func a raw address? */
> - errno = 0;
> - raw_offset = strtoull(func, &func_end, 0);
> - if (!errno && !*func_end) {
> - free(func);
> - func = NULL;
> - offset = (size_t)raw_offset;
> + break;
> + case 3:
> + case 4:
> + opts.retprobe = str_has_pfx(prog->sec_name, "uretprobe");
you just parsed probe_type, strcmp() against that instead, no need for
prefix check
> + if (opts.retprobe && offset != 0) {
> + pr_warn("uretprobes do not support offset specification\n");
> + break;
> + }
> + opts.func_name = func_name;
> + *link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
> + ret = libbpf_get_error(*link);
> + break;
> + default:
> + pr_warn("uprobe name '%s' is invalid\n", prog->sec_name);
Add "prog '%s': " prefix. Also, the section name is not an uprobe
name. Maybe "prog '%s': invalid format of section definition '%s'\n"?
> + break;
> }
> - opts.func_name = func;
> + free(probe_type);
> + free(binary_path);
> + free(func_name);
>
> - *link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
> - free(func);
> - return libbpf_get_error(*link);
> + return ret;
> }
>
> struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index b6247dc..155702a 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -103,6 +103,11 @@
> #define str_has_pfx(str, pfx) \
> (strncmp(str, pfx, __builtin_constant_p(pfx) ? sizeof(pfx) - 1 : strlen(pfx)) == 0)
>
> +/* similar for suffix */
> +#define str_has_sfx(str, sfx) \
> + (strlen(sfx) <= strlen(str) ? \
> + strncmp(str + strlen(str) - strlen(sfx), sfx, strlen(sfx)) == 0 : 0)
> +
so str_has_pfx() is a macro to avoid strlen() for string literals.
Here you don't do any optimization like that and instead calculating
and recalculating strlen() multiple times. Just make this a static
inline helper function?
and you don't need strncmp() anymore, strcmp() is as safe after all
the strlen() checks and calculations
> /* Symbol versioning is different between static and shared library.
> * Properly versioned symbols are needed for shared library, but
> * only the symbol of the new version is needed for static library.
> --
> 1.8.3.1
>
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