libc: add getauxval()
Add support for getauxval(). This method allows a program an easy way
to retrieve information from the kernel auxiliary vector, and will
hopefully replace other clumsy ways of accessing this same information.
This particular function was also added to glibc in glibc 2.16.
See the following URLs for more details.
* http://lwn.net/Articles/519085/
* http://www.gnu.org/software/libc/manual/html_node/Auxiliary-Vector.html
This change is a prerequisite for bug 7959813.
Bug: http://code.google.com/p/android/issues/detail?id=38441
Change-Id: Iba19d899df334bddc6f4899077ece2fc87564ea8
diff --git a/libc/bionic/libc_init_static.c b/libc/bionic/libc_init_static.c
index ba7f008..bb3a410 100644
--- a/libc/bionic/libc_init_static.c
+++ b/libc/bionic/libc_init_static.c
@@ -49,6 +49,7 @@
#include <bionic_tls.h>
#include <errno.h>
#include <sys/mman.h>
+#include <sys/auxv.h>
// Returns the address of the page containing address 'x'.
#define PAGE_START(x) ((x) & PAGE_MASK)
@@ -65,27 +66,13 @@
}
}
-/*
- * Find the value of the AT_* variable passed to us by the kernel.
- */
-static unsigned find_aux(unsigned *vecs, unsigned type) {
- while (vecs[0]) {
- if (vecs[0] == type) {
- return vecs[1];
- }
- vecs += 2;
- }
-
- return 0; // should never happen
-}
-
-static void apply_gnu_relro(unsigned *vecs) {
+static void apply_gnu_relro() {
Elf32_Phdr *phdr_start;
- unsigned phdr_ct;
+ unsigned long int phdr_ct;
Elf32_Phdr *phdr;
- phdr_start = (Elf32_Phdr *) find_aux(vecs, AT_PHDR);
- phdr_ct = find_aux(vecs, AT_PHNUM);
+ phdr_start = (Elf32_Phdr *) getauxval(AT_PHDR);
+ phdr_ct = getauxval(AT_PHNUM);
for (phdr = phdr_start; phdr < (phdr_start + phdr_ct); phdr++) {
if (phdr->p_type != PT_GNU_RELRO)
@@ -108,7 +95,6 @@
{
int argc;
char **argv, **envp;
- unsigned *vecs;
__libc_init_tls(NULL);
@@ -129,14 +115,6 @@
argv = (char**)(elfdata + 1);
envp = argv + argc + 1;
- // The auxiliary vector is at the end of the environment block
- vecs = (unsigned *) envp;
- while (vecs[0] != 0) {
- vecs++;
- }
- /* The end of the environment block is marked by two NULL pointers */
- vecs++;
-
/* The executable may have its own destructors listed in its .fini_array
* so we need to ensure that these are called when the program exits
* normally.
@@ -144,6 +122,6 @@
if (structors->fini_array)
__cxa_atexit(__libc_fini,structors->fini_array,NULL);
- apply_gnu_relro(vecs);
+ apply_gnu_relro();
exit(slingshot(argc, argv, envp));
}