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am 20b94c0c: Merge "linker: don\'t perform unnecessary mprotects"

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* commit '20b94c0ce99ea3d2315535091c8bcd02f831d252':
  linker: don't perform unnecessary mprotects
This commit is contained in:
Nick Kralevich 2012-08-13 09:46:43 -07:00 committed by Android Git Automerger
commit 89fd9eccdc
2 changed files with 28 additions and 48 deletions
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75
linker/linker.cpp
View File

@ -81,7 +81,7 @@
*/
static int soinfo_link_image(soinfo *si, unsigned wr_offset);
static int soinfo_link_image(soinfo *si);
static int socount = 0;
static soinfo sopool[SO_MAX];
@ -817,20 +817,6 @@ static soinfo* load_library(const char* name)
return NULL;
}
/* Unprotect the segments, i.e. make them writable, to allow
* relocations to work properly. We will later call
* phdr_table_protect_segments() after all of them are applied
* and all constructors are run.
*/
ret = phdr_table_unprotect_segments(phdr_table,
phdr_count,
load_bias);
if (ret < 0) {
DL_ERR("can't unprotect loadable segments for \"%s\": %s",
name, strerror(errno));
return NULL;
}
soinfo_ptr si(name);
if (si.ptr == NULL) {
return NULL;
@ -855,14 +841,12 @@ static soinfo* load_library(const char* name)
static soinfo *
init_library(soinfo *si)
{
unsigned wr_offset = 0xffffffff;
/* At this point we know that whatever is loaded @ base is a valid ELF
* shared library whose segments are properly mapped in. */
TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n",
pid, si->base, si->size, si->name);
if(soinfo_link_image(si, wr_offset)) {
if(soinfo_link_image(si)) {
/* We failed to link. However, we can only restore libbase
** if no additional libraries have moved it since we updated it.
*/
@ -1432,7 +1416,7 @@ static int nullify_closed_stdio (void)
return return_value;
}
static int soinfo_link_image(soinfo *si, unsigned wr_offset)
static int soinfo_link_image(soinfo *si)
{
unsigned *d;
/* "base" might wrap around UINT32_MAX. */
@ -1466,20 +1450,6 @@ static int soinfo_link_image(soinfo *si, unsigned wr_offset)
&si->ARM_exidx, &si->ARM_exidx_count);
#endif
if (si->flags & (FLAG_EXE | FLAG_LINKER)) {
if (phdr_table_unprotect_segments(si->phdr,
si->phnum,
si->load_bias) < 0) {
/* We can't call DL_ERR if the linker's relocations haven't
* been performed yet */
if (!relocating_linker) {
DL_ERR("can't unprotect segments for \"%s\": %s",
si->name, strerror(errno));
}
goto fail;
}
}
/* extract useful information from dynamic section */
for(d = si->dynamic; *d; d++){
DEBUG("%5d d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", pid, d, d[0], d[1]);
@ -1562,13 +1532,7 @@ static int soinfo_link_image(soinfo *si, unsigned wr_offset)
si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr);
break;
case DT_TEXTREL:
/* TODO: make use of this. */
/* this means that we might have to write into where the text
* segment was loaded during relocation... Do something with
* it.
*/
DEBUG("%5d Text segment should be writable during relocation.\n",
pid);
si->has_text_relocations = true;
break;
#if defined(ANDROID_MIPS_LINKER)
case DT_NEEDED:
@ -1664,6 +1628,19 @@ static int soinfo_link_image(soinfo *si, unsigned wr_offset)
}
}
if (si->has_text_relocations) {
/* Unprotect the segments, i.e. make them writable, to allow
* text relocations to work properly. We will later call
* phdr_table_protect_segments() after all of them are applied
* and all constructors are run.
*/
if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't unprotect loadable segments for \"%s\": %s",
si->name, strerror(errno));
goto fail;
}
}
if(si->plt_rel) {
DEBUG("[ %5d relocating %s plt ]\n", pid, si->name );
if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count))
@ -1684,12 +1661,14 @@ static int soinfo_link_image(soinfo *si, unsigned wr_offset)
si->flags |= FLAG_LINKED;
DEBUG("[ %5d finished linking %s ]\n", pid, si->name);
/* All relocations are done, we can protect our segments back to
* read-only. */
if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't protect segments for \"%s\": %s",
si->name, strerror(errno));
goto fail;
if (si->has_text_relocations) {
/* All relocations are done, we can protect our segments back to
* read-only. */
if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) {
DL_ERR("can't protect segments for \"%s\": %s",
si->name, strerror(errno));
goto fail;
}
}
/* We can also turn on GNU RELRO protection */
@ -1911,7 +1890,7 @@ sanitize:
parse_LD_LIBRARY_PATH(ldpath_env);
parse_LD_PRELOAD(ldpreload_env);
if(soinfo_link_image(si, 0)) {
if(soinfo_link_image(si)) {
char errmsg[] = "CANNOT LINK EXECUTABLE\n";
write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf));
write(2, errmsg, sizeof(errmsg));
@ -2050,7 +2029,7 @@ extern "C" unsigned __linker_init(unsigned **elfdata) {
linker_so.phnum = elf_hdr->e_phnum;
linker_so.flags |= FLAG_LINKER;
if (soinfo_link_image(&linker_so, 0)) {
if (soinfo_link_image(&linker_so)) {
// It would be nice to print an error message, but if the linker
// can't link itself, there's no guarantee that we'll be able to
// call write() (because it involves a GOT reference).

1
linker/linker.h
View File

@ -176,6 +176,7 @@ struct soinfo
/* When you read a virtual address from the ELF file, add this
* value to get the corresponding address in the process' address space */
Elf32_Addr load_bias;
int has_text_relocations;
};