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linker: Make the errors reported by dlopen/dlsym be more useful.

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Changed it so that when the linker generates error messages, they are
scribbled away into a buffer that dlfcn and friends can read from.

Since the error messages are generetad with snprintf, and snprintf
MAY call malloc during some code paths, we now link against a version
of libc that does not contain malloc/free/realloc/calloc. We then define
malloc and friends in the dynamic loader, and make them abort() if they
are ever called.

Signed-off-by: Dima Zavin <dima@android.com>
This commit is contained in:
Dima Zavin 2009-05-20 18:28:09 -07:00
parent 49e5533278
commit 2e85579c34
5 changed files with 106 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
linker/Android.mk
View File

@ -37,7 +37,7 @@ endif
LOCAL_MODULE:= linker
LOCAL_STATIC_LIBRARIES := libcutils libc
LOCAL_STATIC_LIBRARIES := libcutils libc_nomalloc
#LOCAL_FORCE_STATIC_EXECUTABLE := true # not necessary when not including BUILD_EXECUTABLE

43
linker/dlfcn.c
View File

@ -15,41 +15,49 @@
*/
#include <dlfcn.h>
#include <pthread.h>
#include <stdio.h>
#include "linker.h"
/* This file hijacks the symbols stubbed out in libdl.so. */
#define DL_SUCCESS 0
#define DL_ERR_CANNOT_FIND_LIBRARY 1
#define DL_ERR_CANNOT_LOAD_LIBRARY 1
#define DL_ERR_INVALID_LIBRARY_HANDLE 2
#define DL_ERR_BAD_SYMBOL_NAME 3
#define DL_ERR_SYMBOL_NOT_FOUND 4
#define DL_ERR_SYMBOL_NOT_GLOBAL 5
static char dl_err_buf[1024];
static const char *dl_err_str;
static const char *dl_errors[] = {
[DL_SUCCESS] = NULL,
[DL_ERR_CANNOT_FIND_LIBRARY] = "Cannot find library",
[DL_ERR_CANNOT_LOAD_LIBRARY] = "Cannot load library",
[DL_ERR_INVALID_LIBRARY_HANDLE] = "Invalid library handle",
[DL_ERR_BAD_SYMBOL_NAME] = "Invalid symbol name",
[DL_ERR_SYMBOL_NOT_FOUND] = "Symbol not found",
[DL_ERR_SYMBOL_NOT_GLOBAL] = "Symbol is not global",
};
static int dl_last_err = DL_SUCCESS;
#define likely(expr) __builtin_expect (expr, 1)
#define unlikely(expr) __builtin_expect (expr, 0)
static pthread_mutex_t dl_lock = PTHREAD_MUTEX_INITIALIZER;
void *dlopen(const char *filename, int flag)
static void set_dlerror(int err)
{
snprintf(dl_err_buf, sizeof(dl_err_buf), "%s: %s", dl_errors[err],
linker_get_error());
dl_err_str = (const char *)&dl_err_buf[0];
};
void *dlopen(const char *filename, int flag)
{
soinfo *ret;
pthread_mutex_lock(&dl_lock);
ret = find_library(filename);
if (unlikely(ret == NULL)) {
dl_last_err = DL_ERR_CANNOT_FIND_LIBRARY;
set_dlerror(DL_ERR_CANNOT_LOAD_LIBRARY);
} else {
ret->refcount++;
}
@ -59,9 +67,9 @@ void *dlopen(const char *filename, int flag)
const char *dlerror(void)
{
const char *err = dl_errors[dl_last_err];
dl_last_err = DL_SUCCESS;
return err;
const char *tmp = dl_err_str;
dl_err_str = NULL;
return (const char *)tmp;
}
void *dlsym(void *handle, const char *symbol)
@ -71,16 +79,16 @@ void *dlsym(void *handle, const char *symbol)
unsigned bind;
pthread_mutex_lock(&dl_lock);
if(unlikely(handle == 0)) {
dl_last_err = DL_ERR_INVALID_LIBRARY_HANDLE;
set_dlerror(DL_ERR_INVALID_LIBRARY_HANDLE);
goto err;
}
if(unlikely(symbol == 0)) {
dl_last_err = DL_ERR_BAD_SYMBOL_NAME;
set_dlerror(DL_ERR_BAD_SYMBOL_NAME);
goto err;
}
if(handle == RTLD_DEFAULT) {
sym = lookup(symbol, &base);
} else if(handle == RTLD_NEXT) {
@ -92,16 +100,17 @@ void *dlsym(void *handle, const char *symbol)
if(likely(sym != 0)) {
bind = ELF32_ST_BIND(sym->st_info);
if(likely((bind == STB_GLOBAL) && (sym->st_shndx != 0))) {
unsigned ret = sym->st_value + base;
pthread_mutex_unlock(&dl_lock);
return (void*)ret;
}
dl_last_err = DL_ERR_SYMBOL_NOT_GLOBAL;
set_dlerror(DL_ERR_SYMBOL_NOT_GLOBAL);
}
else dl_last_err = DL_ERR_SYMBOL_NOT_FOUND;
else
set_dlerror(DL_ERR_SYMBOL_NOT_FOUND);
err:
pthread_mutex_unlock(&dl_lock);

113
linker/linker.c
View File

@ -104,6 +104,31 @@ unsigned bitmask[4096];
#define PT_ARM_EXIDX 0x70000001 /* .ARM.exidx segment */
#endif
#define HOODLUM(name, ret, ...) \
ret name __VA_ARGS__ \
{ \
char errstr[] = "ERROR: " #name " called from the dynamic linker!\n"; \
write(2, errstr, sizeof(errstr)); \
abort(); \
}
HOODLUM(malloc, void *, (size_t size));
HOODLUM(free, void, (void *ptr));
HOODLUM(realloc, void *, (void *ptr, size_t size));
HOODLUM(calloc, void *, (size_t cnt, size_t size));
static char __linker_dl_err_buf[768];
#define DL_ERR(fmt, x...) \
do { \
snprintf(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), \
"%s[%d]: " fmt, __func__, __LINE__, ##x); \
ERROR(fmt, ##x); \
} while(0)
const char *linker_get_error(void)
{
return (const char *)&__linker_dl_err_buf[0];
}
/*
* This function is an empty stub where GDB locates a breakpoint to get notified
* about linker activity.
@ -207,7 +232,7 @@ static soinfo *alloc_info(const char *name)
soinfo *si;
if(strlen(name) >= SOINFO_NAME_LEN) {
ERROR("%5d library name %s too long\n", pid, name);
DL_ERR("%5d library name %s too long\n", pid, name);
return 0;
}
@ -216,7 +241,7 @@ static soinfo *alloc_info(const char *name)
*/
if (!freelist) {
if(socount == SO_MAX) {
ERROR("%5d too many libraries when loading %s\n", pid, name);
DL_ERR("%5d too many libraries when loading %s\n", pid, name);
return NULL;
}
freelist = sopool + socount++;
@ -252,7 +277,7 @@ static void free_info(soinfo *si)
}
if (trav == NULL) {
/* si was not ni solist */
ERROR("%5d name %s is not in solist!\n", pid, si->name);
DL_ERR("%5d name %s is not in solist!\n", pid, si->name);
return;
}
@ -521,7 +546,7 @@ is_prelinked(int fd, const char *name)
sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END);
if (sz < 0) {
ERROR("lseek() failed!\n");
DL_ERR("lseek() failed!\n");
return 0;
}
@ -597,7 +622,7 @@ get_lib_extents(int fd, const char *name, void *__hdr, unsigned *total_sz)
TRACE("[ %5d Computing extents for '%s'. ]\n", pid, name);
if (verify_elf_object(_hdr, name) < 0) {
ERROR("%5d - %s is not a valid ELF object\n", pid, name);
DL_ERR("%5d - %s is not a valid ELF object\n", pid, name);
return (unsigned)-1;
}
@ -625,7 +650,7 @@ get_lib_extents(int fd, const char *name, void *__hdr, unsigned *total_sz)
}
if ((min_vaddr == 0xffffffff) && (max_vaddr == 0)) {
ERROR("%5d - No loadable segments found in %s.\n", pid, name);
DL_ERR("%5d - No loadable segments found in %s.\n", pid, name);
return (unsigned)-1;
}
@ -661,13 +686,13 @@ static int reserve_mem_region(soinfo *si)
void *base = mmap((void *)si->base, si->size, PROT_READ | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (base == MAP_FAILED) {
ERROR("%5d can NOT map (%sprelinked) library '%s' at 0x%08x "
DL_ERR("%5d can NOT map (%sprelinked) library '%s' at 0x%08x "
"as requested, will try general pool: %d (%s)\n",
pid, (si->base ? "" : "non-"), si->name, si->base,
errno, strerror(errno));
return -1;
} else if (base != (void *)si->base) {
ERROR("OOPS: %5d %sprelinked library '%s' mapped at 0x%08x, "
DL_ERR("OOPS: %5d %sprelinked library '%s' mapped at 0x%08x, "
"not at 0x%08x\n", pid, (si->base ? "" : "non-"),
si->name, (unsigned)base, si->base);
munmap(base, si->size);
@ -705,7 +730,7 @@ alloc_mem_region(soinfo *si)
}
err:
ERROR("OOPS: %5d cannot map library '%s'. no vspace available.\n",
DL_ERR("OOPS: %5d cannot map library '%s'. no vspace available.\n",
pid, si->name);
return -1;
}
@ -764,7 +789,7 @@ load_segments(int fd, void *header, soinfo *si)
MAP_PRIVATE | MAP_FIXED, fd,
phdr->p_offset & (~PAGE_MASK));
if (pbase == MAP_FAILED) {
ERROR("%d failed to map segment from '%s' @ 0x%08x (0x%08x). "
DL_ERR("%d failed to map segment from '%s' @ 0x%08x (0x%08x). "
"p_vaddr=0x%08x p_offset=0x%08x\n", pid, si->name,
(unsigned)tmp, len, phdr->p_vaddr, phdr->p_offset);
goto fail;
@ -820,8 +845,8 @@ load_segments(int fd, void *header, soinfo *si)
MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS,
-1, 0);
if (extra_base == MAP_FAILED) {
ERROR("[ %5d - failed to extend segment from '%s' @ 0x%08x "
"(0x%08x) ]\n", pid, si->name, (unsigned)tmp,
DL_ERR("[ %5d - failed to extend segment from '%s' @ 0x%08x"
" (0x%08x) ]\n", pid, si->name, (unsigned)tmp,
extra_len);
goto fail;
}
@ -873,7 +898,7 @@ load_segments(int fd, void *header, soinfo *si)
/* Sanity check */
if (total_sz > si->size) {
ERROR("%5d - Total length (0x%08x) of mapped segments from '%s' is "
DL_ERR("%5d - Total length (0x%08x) of mapped segments from '%s' is "
"greater than what was allocated (0x%08x). THIS IS BAD!\n",
pid, total_sz, si->name, si->size);
goto fail;
@ -940,18 +965,20 @@ load_library(const char *name)
soinfo *si = NULL;
Elf32_Ehdr *hdr;
if(fd == -1)
if(fd == -1) {
DL_ERR("Library '%s' not found\n", name);
return NULL;
}
/* We have to read the ELF header to figure out what to do with this image
*/
if (lseek(fd, 0, SEEK_SET) < 0) {
ERROR("lseek() failed!\n");
DL_ERR("lseek() failed!\n");
goto fail;
}
if ((cnt = read(fd, &__header[0], PAGE_SIZE)) < 0) {
ERROR("read() failed!\n");
DL_ERR("read() failed!\n");
goto fail;
}
@ -1042,8 +1069,8 @@ soinfo *find_library(const char *name)
if(!strcmp(name, si->name)) {
if(si->flags & FLAG_ERROR) return 0;
if(si->flags & FLAG_LINKED) return si;
ERROR("OOPS: %5d recursive link to '%s'\n", pid, si->name);
return 0;
DL_ERR("OOPS: %5d recursive link to '%s'\n", pid, si->name);
return NULL;
}
}
@ -1074,7 +1101,7 @@ unsigned unload_library(soinfo *si)
if(lsi)
unload_library(lsi);
else
ERROR("%5d could not unload '%s'\n",
DL_ERR("%5d could not unload '%s'\n",
pid, si->strtab + d[1]);
}
}
@ -1124,19 +1151,19 @@ static int reloc_library(soinfo *si, Elf32_Rel *rel, unsigned count)
sym_name = (char *)(strtab + symtab[sym].st_name);
s = _do_lookup(si, sym_name, &base);
if(s == 0) {
ERROR("%5d cannot locate '%s'...\n", pid, sym_name);
DL_ERR("%5d cannot locate '%s'...\n", pid, sym_name);
return -1;
}
#if 0
if((base == 0) && (si->base != 0)){
/* linking from libraries to main image is bad */
ERROR("%5d cannot locate '%s'...\n",
DL_ERR("%5d cannot locate '%s'...\n",
pid, strtab + symtab[sym].st_name);
return -1;
}
#endif
if ((s->st_shndx == SHN_UNDEF) && (s->st_value != 0)) {
ERROR("%5d In '%s', shndx=%d && value=0x%08x. We do not "
DL_ERR("%5d In '%s', shndx=%d && value=0x%08x. We do not "
"handle this yet\n", pid, si->name, s->st_shndx,
s->st_value);
return -1;
@ -1198,7 +1225,7 @@ static int reloc_library(soinfo *si, Elf32_Rel *rel, unsigned count)
COUNT_RELOC(RELOC_RELATIVE);
MARK(rel->r_offset);
if(sym){
ERROR("%5d odd RELATIVE form...\n", pid);
DL_ERR("%5d odd RELATIVE form...\n", pid);
return -1;
}
TRACE_TYPE(RELO, "%5d RELO RELATIVE %08x <- +%08x\n", pid,
@ -1239,7 +1266,7 @@ static int reloc_library(soinfo *si, Elf32_Rel *rel, unsigned count)
#endif /* ANDROID_ARM_LINKER */
default:
ERROR("%5d unknown reloc type %d @ %p (%d)\n",
DL_ERR("%5d unknown reloc type %d @ %p (%d)\n",
pid, type, rel, (int) (rel - start));
return -1;
}
@ -1296,9 +1323,9 @@ static void call_constructors(soinfo *si)
TRACE("[ %5d Done calling preinit_array for '%s' ]\n", pid, si->name);
} else {
if (si->preinit_array) {
ERROR("%5d Shared library '%s' has a preinit_array table @ 0x%08x."
" This is INVALID.\n", pid, si->name,
(unsigned)si->preinit_array);
DL_ERR("%5d Shared library '%s' has a preinit_array table @ 0x%08x."
" This is INVALID.\n", pid, si->name,
(unsigned)si->preinit_array);
}
}
@ -1344,7 +1371,7 @@ static int nullify_closed_stdio (void)
dev_null = open("/dev/null", O_RDWR);
if (dev_null < 0) {
ERROR("Cannot open /dev/null.\n");
DL_ERR("Cannot open /dev/null.\n");
return -1;
}
TRACE("[ %5d Opened /dev/null file-descriptor=%d]\n", pid, dev_null);
@ -1370,7 +1397,7 @@ static int nullify_closed_stdio (void)
/* The only error we allow is that the file descriptor does not
exist, in which case we dup /dev/null to it. */
if (errno != EBADF) {
ERROR("nullify_stdio: unhandled error %s\n", strerror(errno));
DL_ERR("nullify_stdio: unhandled error %s\n", strerror(errno));
return_value = -1;
continue;
}
@ -1381,9 +1408,9 @@ static int nullify_closed_stdio (void)
do {
status = dup2(dev_null, i);
} while (status < 0 && errno == EINTR);
if (status < 0) {
ERROR("nullify_stdio: dup2 error %s\n", strerror(errno));
DL_ERR("nullify_stdio: dup2 error %s\n", strerror(errno));
return_value = -1;
continue;
}
@ -1392,12 +1419,12 @@ static int nullify_closed_stdio (void)
/* If /dev/null is not one of the stdio file descriptors, close it. */
if (dev_null > 2) {
TRACE("[ %5d Closing /dev/null file-descriptor=%d]\n", pid, dev_null);
do {
do {
status = close(dev_null);
} while (status < 0 && errno == EINTR);
if (status < 0) {
ERROR("nullify_stdio: close error %s\n", strerror(errno));
DL_ERR("nullify_stdio: close error %s\n", strerror(errno));
return_value = -1;
}
}
@ -1465,7 +1492,7 @@ static int link_image(soinfo *si, unsigned wr_offset)
}
} else if (phdr->p_type == PT_DYNAMIC) {
if (si->dynamic != (unsigned *)-1) {
ERROR("%5d multiple PT_DYNAMIC segments found in '%s'. "
DL_ERR("%5d multiple PT_DYNAMIC segments found in '%s'. "
"Segment at 0x%08x, previously one found at 0x%08x\n",
pid, si->name, si->base + phdr->p_vaddr,
(unsigned)si->dynamic);
@ -1478,7 +1505,7 @@ static int link_image(soinfo *si, unsigned wr_offset)
}
if (si->dynamic == (unsigned *)-1) {
ERROR("%5d missing PT_DYNAMIC?!\n", pid);
DL_ERR("%5d missing PT_DYNAMIC?!\n", pid);
goto fail;
}
@ -1502,7 +1529,7 @@ static int link_image(soinfo *si, unsigned wr_offset)
break;
case DT_PLTREL:
if(*d != DT_REL) {
ERROR("DT_RELA not supported\n");
DL_ERR("DT_RELA not supported\n");
goto fail;
}
break;
@ -1527,7 +1554,7 @@ static int link_image(soinfo *si, unsigned wr_offset)
*d = (int) &_r_debug;
break;
case DT_RELA:
ERROR("%5d DT_RELA not supported\n", pid);
DL_ERR("%5d DT_RELA not supported\n", pid);
goto fail;
case DT_INIT:
si->init_func = (void (*)(void))(si->base + *d);
@ -1579,16 +1606,16 @@ static int link_image(soinfo *si, unsigned wr_offset)
pid, si->base, si->strtab, si->symtab);
if((si->strtab == 0) || (si->symtab == 0)) {
ERROR("%5d missing essential tables\n", pid);
DL_ERR("%5d missing essential tables\n", pid);
goto fail;
}
for(d = si->dynamic; *d; d += 2) {
if(d[0] == DT_NEEDED){
DEBUG("%5d %s needs %s\n", pid, si->name, si->strtab + d[1]);
soinfo *lsi = find_library(si->strtab + d[1]);
soinfo *lsi = find_library(si->strtab + d[1]);
if(lsi == 0) {
ERROR("%5d could not load '%s'\n", pid, si->strtab + d[1]);
DL_ERR("%5d could not load '%s'\n", pid, si->strtab + d[1]);
goto fail;
}
lsi->refcount++;
@ -1747,8 +1774,10 @@ unsigned __linker_init(unsigned **elfdata)
si->wrprotect_start = 0xffffffff;
si->wrprotect_end = 0;
if(link_image(si, 0)){
ERROR("CANNOT LINK EXECUTABLE '%s'\n", argv[0]);
if(link_image(si, 0)) {
char errmsg[] = "CANNOT LINK EXECUTABLE\n";
write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf));
write(2, errmsg, sizeof(errmsg));
exit(-1);
}

1
linker/linker.h
View File

@ -204,6 +204,7 @@ soinfo *find_library(const char *name);
unsigned unload_library(soinfo *si);
Elf32_Sym *lookup_in_library(soinfo *si, const char *name);
Elf32_Sym *lookup(const char *name, unsigned *base);
const char *linker_get_error(void);
#ifdef ANDROID_ARM_LINKER
typedef long unsigned int *_Unwind_Ptr;

14
linker/linker_debug.h
View File

@ -55,17 +55,16 @@
#define TRUE 1
#define FALSE 0
#define __PRINTVF(v,f,x...) do { \
(debug_verbosity > (v)) && (printf(x), ((f) && fflush(stdout))); \
} while (0)
/* Only use printf() during debugging. We have seen occasional memory
* corruption when the linker uses printf().
*/
#if LINKER_DEBUG
extern int debug_verbosity;
#warning "*** LINKER IS USING printf(); DO NOT CHECK THIS IN ***"
#define _PRINTVF(v,f,x...) __PRINTVF(v,f,x)
#define _PRINTVF(v,f,x...) \
do { \
(debug_verbosity > (v)) && (printf(x), ((f) && fflush(stdout))); \
} while (0)
#else /* !LINKER_DEBUG */
#define _PRINTVF(v,f,x...) do {} while(0)
#endif /* LINKER_DEBUG */
@ -75,8 +74,9 @@ extern int debug_verbosity;
#define TRACE(x...) _PRINTVF(1, TRUE, x)
#define WARN(fmt,args...) \
_PRINTVF(-1, TRUE, "%s:%d| WARNING: " fmt, __FILE__, __LINE__, ## args)
#define ERROR(fmt,args...) \
__PRINTVF(-1, TRUE, "%s:%d| ERROR: " fmt, __FILE__, __LINE__, ## args)
#define ERROR(fmt,args...) \
_PRINTVF(-1, TRUE, "%s:%d| ERROR: " fmt, __FILE__, __LINE__, ## args)
#if TRACE_DEBUG
#define DEBUG(x...) _PRINTVF(2, TRUE, "DEBUG: " x)