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[125.237.24.141]) by smtp.gmail.com with ESMTPSA id h1-20020a17090a470100b002194319662asm4025715pjg.42.2023.01.21.17.24.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 21 Jan 2023 17:24:24 -0800 (PST) Date: Sun, 22 Jan 2023 14:24:19 +1300 From: Paulo Miguel Almeida To: Steven Rostedt Cc: linux-trace-devel@vger.kernel.org Subject: Re: [PATCH v3] trace-cmd: Open code execvp routine to avoid multiple execve syscalls Message-ID: References: <20230121122254.53f6dfa6@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230121122254.53f6dfa6@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On Sat, Jan 21, 2023 at 12:22:54PM -0500, Steven Rostedt wrote: > On Sat, 21 Jan 2023 18:50:29 +1300 > Paulo Miguel Almeida wrote: > > > In tracecmd/trace-record.c:, trace-cmd record -F > > is launched via the libc's execvp() routine. The way that execvp() routine > > works is by invoking execve syscall for every entry on the $PATH if > > command specified is neither absolute nor relative which can come across > > as a bit cryptic to untrained eyes. > > > > - absolute path example: > > > > # trace-cmd record -p function_graph \ > > -g __x64_sys_execve -O nofuncgraph-irqs \ > > -n __cond_resched --max-graph-depth 1 \ > > -F /usr/bin/echo "ftrace" > /dev/null > > > > # trace-cmd report > > echo-172994 [000] 185539.798539: funcgraph_entry: ! 803.376 us | __x64_sys_execve(); > > > > - PATH-dependent path example: > > > > # trace-cmd record -p function_graph \ > > -g __x64_sys_execve -O nofuncgraph-irqs \ > > -n __cond_resched --max-graph-depth 1 \ > > -F echo "ftrace" > /dev/null > > > > # trace-cmd report > > echo-172656 [002] 185009.671586: funcgraph_entry: ! 288.732 us | __x64_sys_execve(); > > echo-172656 [002] 185009.671879: funcgraph_entry: ! 158.337 us | __x64_sys_execve(); > > echo-172656 [002] 185009.672042: funcgraph_entry: ! 161.843 us | __x64_sys_execve(); > > echo-172656 [002] 185009.672207: funcgraph_entry: ! 157.656 us | __x64_sys_execve(); > > echo-172656 [002] 185009.672369: funcgraph_entry: ! 156.343 us | __x64_sys_execve(); > > echo-172656 [002] 185009.672529: funcgraph_entry: ! 863.629 us | __x64_sys_execve(); > > > > Open code the libc's execvp routine into trace-cmd so ftrace will only > > start recording once the command is found when it needs to be found in > > PATH. > > > > Signed-off-by: Paulo Miguel Almeida > > --- > > Changelog: > > > > - v3: simplify path traversal code via strtok_r. (Req. Steven Rostedt) > > - v2: open code execvp routine into trace-cmd. (Req. Steven Rostedt) > > - v1: https://lore.kernel.org/linux-trace-devel/Y7dUo6woh9Y31cdl@mail.google.com/ > > --- > > tracecmd/trace-record.c | 48 +++++++++++++++++++++++++++++++++++------ > > 1 file changed, 41 insertions(+), 7 deletions(-) > > > > diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c > > index 7f0cebe..c111ef6 100644 > > --- a/tracecmd/trace-record.c > > +++ b/tracecmd/trace-record.c > > @@ -1683,6 +1683,46 @@ static int change_user(const char *user) > > return 0; > > } > > > > +static void execute_program(int argc, char **argv) > > +{ > > + char buf[PATH_MAX + NAME_MAX + 1]; > > + char *path; > > + char *entry; > > + char *saveptr; > > + > > + /* > > + * if command specified by user is neither absolute nor > > + * relative than we search for it in $PATH. > > + */ > > + if (*argv[0] != '/' && *argv[0] != '.') { > > All you really need to do is check if '/' exists in the name, as the path > lookup in bash will not add PATH in such cases: > > # mkdir /usr/bin/direct > # cp /usr/bin/grep /usr/bin/direct > # direct/grep > -bash: direct/grep: No such file or directory > > So, the above really has to be just "if (strchr(argv[0], '/') == NULL)" > > No need to look for '.'. As you could an application that starts with "." > and it should not think it's a path name in such cases. > > In fact, if you have a '/' in the name. It will use relative paths. > > # mv /usr/bin/direct . > # direct/grep -h > Usage: grep [OPTION]... PATTERNS [FILE]... > Try 'grep --help' for more information. > > So appending PATH in such cases is incorrect, and will produce unexpected > results. > > -- Steve You are right Steve, that case slipped through the cracks somehow. good catch :) I will submit a new one shortly. thanks! - Paulo A. > > > + path = getenv("PATH"); > > + > > + if (!path) > > + die("can't search for '%s' if $PATH is NULL", argv[0]); > > + > > + for (entry = strtok_r(path, ":", &saveptr); > > + entry; entry = strtok_r(NULL, ":", &saveptr)) { > > + > > + snprintf(buf, sizeof(buf), "%s/%s", entry, argv[0]); > > + > > + /* does it exist and can we execute it? */ > > + if (access(buf, X_OK) == 0) > > + break; > > + > > + } > > + } else { > > + strncpy(buf, argv[0], sizeof(buf)); > > + } > > + > > + tracecmd_enable_tracing(); > > + if (execve(buf, argv, environ)) { > > + fprintf(stderr, "\n********************\n"); > > + fprintf(stderr, " Unable to exec %s\n", argv[0]); > > + fprintf(stderr, "********************\n"); > > + die("Failed to exec %s", argv[0]); > > + } > > +} > > + > > static void run_cmd(enum trace_type type, const char *user, int argc, char **argv) > > { > > int status; > > @@ -1693,7 +1733,6 @@ static void run_cmd(enum trace_type type, const char *user, int argc, char **arg > > if (!pid) { > > /* child */ > > update_task_filter(); > > - tracecmd_enable_tracing(); > > if (!fork_process) > > enable_ptrace(); > > /* > > @@ -1709,12 +1748,7 @@ static void run_cmd(enum trace_type type, const char *user, int argc, char **arg > > if (change_user(user) < 0) > > die("Failed to change user to %s", user); > > > > - if (execvp(argv[0], argv)) { > > - fprintf(stderr, "\n********************\n"); > > - fprintf(stderr, " Unable to exec %s\n", argv[0]); > > - fprintf(stderr, "********************\n"); > > - die("Failed to exec %s", argv[0]); > > - } > > + execute_program(argc, argv); > > } > > if (fork_process) > > exit(0); >