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Bug 1839740 - Rename the symbol by elfhack to point to the ELF header. r=firefox-build-system-reviewers,andi

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Elfhack acts as a linker, and it uses the `elf_header` symbol to point
at the ELF header in the injected code that applies relocations.
Both GNU ld and lld expose a `__ehdr_start` symbol with the same meaning,
so rename the `elf_header` symbol for compatibility. This will allow to
reuse the code in the upcoming replacement for elfhack.

Differential Revision: https://phabricator.services.mozilla.com/D187088
This commit is contained in:
Mike Hommey 2023-09-16 19:52:25 +00:00
parent 62b0896fb2
commit 1da6d16d6d
2 changed files with 6 additions and 6 deletions
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4
build/unix/elfhack/elfhack.cpp
View File

@ -474,8 +474,8 @@ class ElfRelHackCode_Section : public ElfSection {
addr = relhack_section.getAddr();
} else if (strcmp(name, "relhack_end") == 0) {
addr = relhack_section.getAddr() + relhack_section.getSize();
} else if (strcmp(name, "elf_header") == 0) {
// TODO: change this ungly hack to something better
} else if (strcmp(name, "__ehdr_start") == 0) {
// TODO: change this ugly hack to something better
ElfSection* ehdr = parent.getSection(1)->getPrevious()->getPrevious();
addr = ehdr->getAddr();
} else if (strcmp(name, "original_init") == 0) {

8
build/unix/elfhack/inject.c
View File

@ -69,7 +69,7 @@ extern __attribute__((visibility("hidden"))) void original_init(int argc,
extern __attribute__((visibility("hidden"))) Elf_Addr relhack[];
extern __attribute__((visibility("hidden"))) Elf_Addr relhack_end[];
extern __attribute__((visibility("hidden"))) Elf_Ehdr elf_header;
extern __attribute__((visibility("hidden"))) Elf_Ehdr __ehdr_start;
extern __attribute__((visibility("hidden"))) int (*mprotect_cb)(void* addr,
size_t len,
@ -82,8 +82,8 @@ static inline __attribute__((always_inline)) void do_relocations(void) {
Elf_Addr* ptr;
for (Elf_Addr* entry = relhack; entry < relhack_end; entry++) {
if ((*entry & 1) == 0) {
ptr = (Elf_Addr*)((intptr_t)&elf_header + *entry);
*ptr += (intptr_t)&elf_header;
ptr = (Elf_Addr*)((intptr_t)&__ehdr_start + *entry);
*ptr += (intptr_t)&__ehdr_start;
} else {
size_t remaining = (8 * sizeof(Elf_Addr) - 1);
Elf_Addr bits = *entry;
@ -92,7 +92,7 @@ static inline __attribute__((always_inline)) void do_relocations(void) {
remaining--;
ptr++;
if (bits & 1) {
*ptr += (intptr_t)&elf_header;
*ptr += (intptr_t)&__ehdr_start;
}
} while (bits);
ptr += remaining;