Bug 234523
| Summary: | elf_aux_info() doesn't expose all AT_* vectors | ||
|---|---|---|---|
| Product: | Base System | Reporter: | Jan Beich <jbeich> |
| Component: | bin | Assignee: | Mitchell Horne <mhorne> |
| Status: | Closed FIXED | ||
| Severity: | Affects Only Me | CC: | cem, mhorne |
| Priority: | --- | ||
| Version: | CURRENT | ||
| Hardware: | Any | ||
| OS: | Any | ||
Hey Jan, I self-assigned this a while ago but never saw it through to completion. From the patches I produced, kib@ expressed that he did not want to expose arbitrary AT_* vectors without an intended use-case. I think what he said was reasonable; some of these vectors have no use or meaning outside of rtld. For the specific case of exposing AT_EXECPATH, it was handled by r354694. I'm marking this PR as fixed, with the understanding that another can be opened in the future if some other use-case requires one of the remaining unexposed vectors. |
KERN_PROC_AUXV allows accessing arbitrary AT_* vectors but libc exposes only few via elf_aux_info(3). For example, one may want to rely on libc caching AT_EXECPATH instead of retrieving KERN_PROC_PATHNAME directly. $ cat elf_aux_info.c #include <sys/auxv.h> #include <limits.h> #include <stdio.h> int main() { char exe[PATH_MAX + 1] = {0}; elf_aux_info(AT_EXECPATH, &exe, sizeof(exe)); printf("%s\n", exe); return 0; } $ make elf_aux_info $ ./elf_aux_info $ vs. $ cat getauxval_naive.c #include <sys/param.h> #include <sys/sysctl.h> #include <elf.h> #include <errno.h> #include <unistd.h> #include <stdio.h> static unsigned long getauxval(unsigned long type) { Elf_Auxinfo auxv[AT_COUNT]; size_t len = sizeof(auxv); int mib[] = { CTL_KERN, KERN_PROC, KERN_PROC_AUXV, getpid(), }; if (sysctl(mib, nitems(mib), auxv, &len, NULL, 0) != -1) { for (size_t i = 0; i < nitems(auxv); i++) if ((unsigned long)auxv[i].a_type == type) return auxv[i].a_un.a_val; errno = ENOENT; } return 0; } int main() { printf("%s\n", (char *)getauxval(AT_EXECPATH)); return 0; } $ make getauxval_naive $ ./getauxval_naive /home/foo/getauxval_naive $