linker: avoid mapping the whole library before load.
This patch changes the load_library() function in the
dynamic linker to avoid reserving a huge read-only
address-space range just to read the ELF header and
program header (which are typically very small and easily
fit in the first page).
Instead, we use the functions in linker_phdr.c to only
load the data that we need in a temporary mmap-allocated
page of memory, which we release when the function exits.
This avoids issues when loading very large libraries, or
simply debug versions that only need to load a tiny percentage
of their overall file content in RAM.
Change-Id: Id3a189fad2119a870a1b3d43dd81380c54ea6044
diff --git a/linker/linker.c b/linker/linker.c
index 93819e4..1bf017f 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -50,6 +50,7 @@
#include "linker_debug.h"
#include "linker_environ.h"
#include "linker_format.h"
+#include "linker_phdr.h"
#define ALLOW_SYMBOLS_FROM_MAIN 1
#define SO_MAX 128
@@ -701,81 +702,6 @@
}
-/* get_lib_extents
- * Retrieves the base (*base) address where the ELF object should be
- * mapped and its overall memory size (*total_sz).
- *
- * Args:
- * fd: Opened file descriptor for the library
- * name: The name of the library
- * _hdr: Pointer to the header page of the library
- * total_sz: Total size of the memory that should be allocated for
- * this library
- *
- * Returns:
- * -1 if there was an error while trying to get the lib extents.
- * The possible reasons are:
- * - Could not determine if the library was prelinked.
- * - The library provided is not a valid ELF object
- * 0 if the library did not request a specific base offset (normal
- * for non-prelinked libs)
- * > 0 if the library requests a specific address to be mapped to.
- * This indicates a pre-linked library.
- */
-static unsigned
-get_lib_extents(int fd, const char *name, void *__hdr, unsigned *total_sz)
-{
- unsigned req_base;
- unsigned min_vaddr = 0xffffffff;
- unsigned max_vaddr = 0;
- unsigned char *_hdr = (unsigned char *)__hdr;
- Elf32_Ehdr *ehdr = (Elf32_Ehdr *)_hdr;
- Elf32_Phdr *phdr;
- int cnt;
-
- TRACE("[ %5d Computing extents for '%s'. ]\n", pid, name);
- if (verify_elf_header(ehdr) < 0) {
- DL_ERR("%5d - %s is not a valid ELF object", pid, name);
- return (unsigned)-1;
- }
-
- req_base = (unsigned) is_prelinked(fd, name);
- if (req_base == (unsigned)-1)
- return -1;
- else if (req_base != 0) {
- TRACE("[ %5d - Prelinked library '%s' requesting base @ 0x%08x ]\n",
- pid, name, req_base);
- } else {
- TRACE("[ %5d - Non-prelinked library '%s' found. ]\n", pid, name);
- }
-
- phdr = (Elf32_Phdr *)(_hdr + ehdr->e_phoff);
-
- /* find the min/max p_vaddrs from all the PT_LOAD segments so we can
- * get the range. */
- for (cnt = 0; cnt < ehdr->e_phnum; ++cnt, ++phdr) {
- if (phdr->p_type == PT_LOAD) {
- if ((phdr->p_vaddr + phdr->p_memsz) > max_vaddr)
- max_vaddr = phdr->p_vaddr + phdr->p_memsz;
- if (phdr->p_vaddr < min_vaddr)
- min_vaddr = phdr->p_vaddr;
- }
- }
-
- if ((min_vaddr == 0xffffffff) && (max_vaddr == 0)) {
- DL_ERR("%5d - No loadable segments found in %s.", pid, name);
- return (unsigned)-1;
- }
-
- /* truncate min_vaddr down to page boundary */
- min_vaddr = PAGE_START(min_vaddr);
-
- /* round max_vaddr up to the next page */
- max_vaddr = PAGE_END(max_vaddr);
-
- *total_sz = (max_vaddr - min_vaddr);
- return (unsigned)req_base;
-}
/* reserve_mem_region
*
* This function reserves a chunk of memory to be used for mapping in
@@ -826,20 +752,15 @@
void *base = mmap(NULL, si->size, PROT_NONE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (base == MAP_FAILED) {
- DL_ERR("%5d mmap of library '%s' failed: %d (%s)\n",
- pid, si->name,
+ DL_ERR("%5d mmap of library '%s' failed (%d bytes): %d (%s)\n",
+ pid, si->name, si->size,
errno, strerror(errno));
- goto err;
+ return -1;
}
si->base = (unsigned) base;
PRINT("%5d mapped library '%s' to %08x via kernel allocator.\n",
pid, si->name, si->base);
return 0;
-
-err:
- DL_ERR("OOPS: %5d cannot map library '%s'. no vspace available.",
- pid, si->name);
- return -1;
}
#define MAYBE_MAP_FLAG(x,from,to) (((x) & (from)) ? (to) : 0)
@@ -861,11 +782,10 @@
* 0 on success, -1 on failure.
*/
static int
-soinfo_load_segments(soinfo* si, int fd, void* header)
+soinfo_load_segments(soinfo* si, int fd, const Elf32_Phdr* phdr_table, int phdr_count, Elf32_Addr ehdr_phoff)
{
- Elf32_Ehdr *ehdr = (Elf32_Ehdr *)header;
- Elf32_Phdr *phdr = (Elf32_Phdr *)((unsigned char *)header + ehdr->e_phoff);
- Elf32_Phdr *phdr0 = 0; /* program header for the first LOAD segment */
+ const Elf32_Phdr *phdr = phdr_table;
+ const Elf32_Phdr *phdr0 = 0; /* program header for the first LOAD segment */
Elf32_Addr base;
int cnt;
unsigned len;
@@ -881,7 +801,7 @@
TRACE("[ %5d - Begin loading segments for '%s' @ 0x%08x ]\n",
pid, si->name, (unsigned)si->base);
- for (cnt = 0; cnt < ehdr->e_phnum; ++cnt, ++phdr) {
+ for (cnt = 0; cnt < phdr_count; ++cnt, ++phdr) {
if (phdr->p_type == PT_LOAD) {
phdr0 = phdr;
@@ -902,8 +822,8 @@
/* Now go through all the PT_LOAD segments and map them into memory
* at the appropriate locations. */
- phdr = (Elf32_Phdr *)((unsigned char *)header + ehdr->e_phoff);
- for (cnt = 0; cnt < ehdr->e_phnum; ++cnt, ++phdr) {
+ phdr = phdr_table;
+ for (cnt = 0; cnt < phdr_count; ++cnt, ++phdr) {
if (phdr->p_type == PT_LOAD) {
DEBUG_DUMP_PHDR(phdr, "PT_LOAD", pid);
/* we want to map in the segment on a page boundary */
@@ -1054,8 +974,8 @@
* phdr ehdr->e_phoff
*/
si->phdr = (Elf32_Phdr *)(base + phdr0->p_vaddr +
- ehdr->e_phoff - phdr0->p_offset);
- si->phnum = ehdr->e_phnum;
+ ehdr_phoff - phdr0->p_offset);
+ si->phnum = phdr_count;
TRACE("[ %5d - Finish loading segments for '%s' @ 0x%08x. "
"Total memory footprint: 0x%08x bytes ]\n", pid, si->name,
@@ -1108,44 +1028,72 @@
}
#endif
+
static soinfo *
load_library(const char *name)
{
int fd = open_library(name);
- int cnt;
+ int ret, cnt;
unsigned ext_sz;
unsigned req_base;
const char *bname;
struct stat sb;
soinfo *si = NULL;
- Elf32_Ehdr *hdr = MAP_FAILED;
+ Elf32_Ehdr header[1];
+ int phdr_count;
+ void* phdr_mmap = NULL;
+ Elf32_Addr phdr_size;
+ const Elf32_Phdr* phdr_table;
if (fd == -1) {
DL_ERR("Library '%s' not found", name);
return NULL;
}
- /* We have to read the ELF header to figure out what to do with this image.
- * Map entire file for this. There won't be much difference in physical
- * memory usage or performance.
- */
- if (fstat(fd, &sb) < 0) {
- DL_ERR("%5d fstat() failed! (%s)", pid, strerror(errno));
+ /* Read the ELF header first */
+ ret = TEMP_FAILURE_RETRY(read(fd, (void*)header, sizeof(header)));
+ if (ret < 0) {
+ DL_ERR("%5d can't read file %s: %s", pid, name, strerror(errno));
+ goto fail;
+ }
+ if (ret != (int)sizeof(header)) {
+ DL_ERR("%5d too small to be an ELF executable: %s", pid, name);
+ goto fail;
+ }
+ if (verify_elf_header(header) < 0) {
+ DL_ERR("%5d not a valid ELF executable: %s", pid, name);
goto fail;
}
- hdr = mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
- if (hdr == MAP_FAILED) {
- DL_ERR("%5d failed to mmap() header of '%s' (%s)",
- pid, name, strerror(errno));
+ /* Then read the program header table */
+ ret = phdr_table_load(fd, header->e_phoff, header->e_phnum,
+ &phdr_mmap, &phdr_size, &phdr_table);
+ if (ret < 0) {
+ DL_ERR("%5d can't load program header table: %s: %s", pid,
+ name, strerror(errno));
+ goto fail;
+ }
+ phdr_count = header->e_phnum;
+
+ /* Get the load extents and the prelinked load address, if any */
+ ext_sz = phdr_table_get_load_size(phdr_table, phdr_count);
+ if (ext_sz == 0) {
+ DL_ERR("%5d no loadable segments in file: %s", pid, name);
goto fail;
}
- /* Parse the ELF header and get the size of the memory footprint for
- * the library */
- req_base = get_lib_extents(fd, name, hdr, &ext_sz);
- if (req_base == (unsigned)-1)
+ req_base = (unsigned) is_prelinked(fd, name);
+ if (req_base == (unsigned)-1) {
+ DL_ERR("%5d can't read end of library: %s: %s", pid, name,
+ strerror(errno));
goto fail;
+ }
+ if (req_base != 0) {
+ TRACE("[ %5d - Prelinked library '%s' requesting base @ 0x%08x ]\n",
+ pid, name, req_base);
+ } else {
+ TRACE("[ %5d - Non-prelinked library '%s' found. ]\n", pid, name);
+ }
TRACE("[ %5d - '%s' (%s) wants base=0x%08x sz=0x%08x ]\n", pid, name,
(req_base ? "prelinked" : "not pre-linked"), req_base, ext_sz);
@@ -1174,17 +1122,19 @@
pid, name, (void *)si->base, (unsigned) ext_sz);
/* Now actually load the library's segments into right places in memory */
- if (soinfo_load_segments(si, fd, hdr) < 0) {
+ if (soinfo_load_segments(si, fd, phdr_table, phdr_count, header->e_phoff) < 0) {
goto fail;
}
- munmap(hdr, sb.st_size);
+ phdr_table_unload(phdr_mmap, phdr_size);
close(fd);
return si;
fail:
if (si) soinfo_free(si);
- if (hdr != MAP_FAILED) munmap(hdr, sb.st_size);
+ if (phdr_mmap != NULL) {
+ phdr_table_unload(phdr_mmap, phdr_size);
+ }
close(fd);
return NULL;
}