65a8b859a
Denys Vlasenko
2016-10-26
Subject
ash: optimize tryexec(): avoid one allocation
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Commit Diff GitHub →
shell/ash.c+11 -20
| @@ -7467,13 +7467,7 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** | |
| #else | |
| execve(cmd, argv, envp); | |
| #endif | |
| - | if (cmd == (char*) bb_busybox_exec_path) { |
| - | /* We already visited ENOEXEC branch below, don't do it again */ |
| - | //TODO: try execve(initial_argv0_of_shell, argv, envp) before giving up? |
| - | free(argv); |
| - | return; |
| - | } |
| - | if (errno == ENOEXEC) { |
| + | if (cmd != (char*) bb_busybox_exec_path && errno == ENOEXEC) { |
| /* Run "cmd" as a shell script: | |
| * http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html | |
| * "If the execve() function fails with ENOEXEC, the shell | |
| @@ -7490,19 +7484,13 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** | |
| * message and exit code 126. For one, this prevents attempts | |
| * to interpret foreign ELF binaries as shell scripts. | |
| */ | |
| - | char **ap; |
| - | char **new; |
| - | |
| - | for (ap = argv; *ap; ap++) |
| - | continue; |
| - | new = ckmalloc((ap - argv + 2) * sizeof(new[0])); |
| - | new[0] = (char*) "ash"; |
| - | new[1] = cmd; |
| - | ap = new + 2; |
| - | while ((*ap++ = *++argv) != NULL) |
| - | continue; |
| + | argv[0] = cmd; |
| cmd = (char*) bb_busybox_exec_path; | |
| - | argv = new; |
| + | /* NB: this is only possible because all callers of shellexec() |
| + | * ensure that the argv[-1] slot exists! |
| + | */ |
| + | argv--; |
| + | argv[0] = (char*) "ash"; |
| goto repeat; | |
| } | |
| } | |
| @@ -7510,6 +7498,7 @@ tryexec(IF_FEATURE_SH_STANDALONE(int applet_no,) char *cmd, char **argv, char ** | |
| /* | |
| * Exec a program. Never returns. If you change this routine, you may | |
| * have to change the find_command routine as well. | |
| + | * argv[-1] must exist and be writable! See tryexec() for why. |
| */ | |
| static void shellexec(char **, const char *, int) NORETURN; | |
| static void | |
| @@ -9415,7 +9404,9 @@ evalcommand(union node *cmd, int flags) | |
| argc++; | |
| } | |
| - | argv = nargv = stalloc(sizeof(char *) * (argc + 1)); |
| + | /* Reserve one extra spot at the front for shellexec. */ |
| + | nargv = stalloc(sizeof(char *) * (argc + 2)); |
| + | argv = ++nargv; |
| for (sp = arglist.list; sp; sp = sp->next) { | |
| TRACE(("evalcommand arg: %s\n", sp->text)); | |
| *nargv++ = sp->text; | |