Add IFUNC support for arm64 and IRELATIVE reloc
There are number of changes in the way IFUNC related relocations are done:
1. IRELATIVE relocations are now supported for x86/x86_64 and arm64.
2. IFUNC relocations are now relying on static linker to generate
them in correct order - this removes necessety of additional
relocation pass for ifuncs.
3. Related to 2: rela?.dyn relocations are preformed before .plt ones.
4. Ifunc are resolved on symbol lookup this approach allowed to avoid
mprotect(PROT_WRITE) call on r-x program segments.
Bug: 17399706
Bug: 17177284
Change-Id: I414dd3e82bd47cc03442c5dfc7c279949aec51ed
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 793ffd5..0e5142a 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -470,32 +470,6 @@
}
}
-void soinfo::resolve_ifunc_symbols() {
- if (!get_has_ifuncs()) {
- return;
- }
-
- phdr_table_unprotect_segments(phdr, phnum, load_bias);
-
- TRACE_TYPE(IFUNC, "CHECKING FOR IFUNCS AND PERFORMING SYMBOL UPDATES");
-
- for (size_t i = 0; i < nchain; ++i) {
- ElfW(Sym)* s = &symtab[i];
- if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
- // The address of the ifunc in the symbol table is the address of the
- // function that chooses the function to which the ifunc will refer.
- // In order to return the proper value, we run the choosing function
- // in the linker and then return its result (minus the base offset).
- TRACE_TYPE(IFUNC, "FOUND IFUNC");
- ElfW(Addr) (*ifunc_ptr)();
- ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + base);
- s->st_value = (ifunc_ptr() - base);
- TRACE_TYPE(IFUNC, "NEW VALUE IS %p", (void*)s->st_value);
- }
- }
- phdr_table_protect_segments(phdr, phnum, load_bias);
-}
-
static unsigned elfhash(const char* _name) {
const unsigned char* name = reinterpret_cast<const unsigned char*>(_name);
unsigned h = 0, g;
@@ -1111,52 +1085,14 @@
protect_data(PROT_READ);
}
-// ifuncs are only defined for x86
-#if defined(__i386__)
-static void soinfo_ifunc_relocate(soinfo* si, ElfW(Rel)* rel, unsigned count) {
- for (size_t idx = 0; idx < count; ++idx, ++rel) {
- ElfW(Sym)* s;
- soinfo* lsi;
- unsigned type = ELFW(R_TYPE)(rel->r_info);
- unsigned sym = ELFW(R_SYM)(rel->r_info);
- ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rel->r_offset + si->load_bias);
- ElfW(Addr) sym_addr = 0;
- const char* sym_name = nullptr;
- sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
- s = soinfo_do_lookup(si, sym_name, &lsi);
+static ElfW(Addr) call_ifunc_resolver(ElfW(Addr) resolver_addr) {
+ typedef ElfW(Addr) (*ifunc_resolver_t)(void);
+ ifunc_resolver_t ifunc_resolver = reinterpret_cast<ifunc_resolver_t>(resolver_addr);
+ ElfW(Addr) ifunc_addr = ifunc_resolver();
+ TRACE_TYPE(RELO, "Called ifunc_resolver@%p. The result is %p", ifunc_resolver, reinterpret_cast<void*>(ifunc_addr));
- if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC && type == R_386_JMP_SLOT) {
- TRACE("IFUNC RELOCATION, PASS 2: %p", (void*)(sym_addr));
- ElfW(Addr) (*ifunc_ptr)();
- ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + si->base);
- *reinterpret_cast<ElfW(Addr)*>(reloc) = ifunc_ptr();
- }
- }
+ return ifunc_addr;
}
-#endif
-
-#if defined(__x86_64__)
-static void soinfo_ifunc_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count) {
- for (size_t idx = 0; idx < count; ++idx, ++rela) {
- ElfW(Sym)* s;
- soinfo* lsi;
- unsigned type = ELFW(R_TYPE)(rela->r_info);
- unsigned sym = ELFW(R_SYM)(rela->r_info);
- ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rela->r_offset + si->load_bias);
- ElfW(Addr) sym_addr = 0;
- const char* sym_name = nullptr;
- sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
- s = soinfo_do_lookup(si, sym_name, &lsi);
-
- if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC && type == R_X86_64_JUMP_SLOT) {
- TRACE("IFUNC RELOCATION, PASS 2: %p", (void*)(sym_addr + rela->r_addend));
- ElfW(Addr) (*ifunc_ptr)();
- ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + si->base);
- *reinterpret_cast<ElfW(Addr)*>(reloc) = ifunc_ptr();
- }
- }
-}
-#endif
#if defined(USE_RELA)
int soinfo::Relocate(ElfW(Rela)* rela, unsigned count) {
@@ -1206,6 +1142,7 @@
case R_AARCH64_ABS32:
case R_AARCH64_ABS16:
case R_AARCH64_RELATIVE:
+ case R_AARCH64_IRELATIVE:
/*
* The sym_addr was initialized to be zero above, or the relocation
* code below does not care about value of sym_addr.
@@ -1218,6 +1155,7 @@
case R_X86_64_32:
case R_X86_64_64:
case R_X86_64_RELATIVE:
+ case R_X86_64_IRELATIVE:
// No need to do anything.
break;
case R_X86_64_PC32:
@@ -1230,7 +1168,7 @@
}
} else {
// We got a definition.
- sym_addr = static_cast<ElfW(Addr)>(s->st_value + lsi->load_bias);
+ sym_addr = lsi->resolve_symbol_address(s);
}
count_relocation(kRelocSymbol);
}
@@ -1342,6 +1280,13 @@
*reinterpret_cast<ElfW(Addr)*>(reloc) = (base + rela->r_addend);
break;
+ case R_AARCH64_IRELATIVE:
+ count_relocation(kRelocRelative);
+ MARK(rela->r_offset);
+ TRACE_TYPE(RELO, "RELO IRELATIVE %16llx <- %16llx\n", reloc, (base + rela->r_addend));
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = call_ifunc_resolver(base + rela->r_addend);
+ break;
+
case R_AARCH64_COPY:
/*
* ET_EXEC is not supported so this should not happen.
@@ -1368,11 +1313,7 @@
MARK(rela->r_offset);
TRACE_TYPE(RELO, "RELO JMP_SLOT %08zx <- %08zx %s", static_cast<size_t>(reloc),
static_cast<size_t>(sym_addr + rela->r_addend), sym_name);
- if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
- set_has_ifuncs(true);
- } else {
- *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
- }
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
break;
case R_X86_64_GLOB_DAT:
count_relocation(kRelocAbsolute);
@@ -1392,6 +1333,12 @@
static_cast<size_t>(base));
*reinterpret_cast<ElfW(Addr)*>(reloc) = base + rela->r_addend;
break;
+ case R_X86_64_IRELATIVE:
+ count_relocation(kRelocRelative);
+ MARK(rela->r_offset);
+ TRACE_TYPE(RELO, "RELO IRELATIVE %16llx <- %16llx\n", reloc, (base + rela->r_addend));
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = call_ifunc_resolver(base + rela->r_addend);
+ break;
case R_X86_64_32:
count_relocation(kRelocRelative);
MARK(rela->r_offset);
@@ -1481,6 +1428,7 @@
case R_386_GLOB_DAT:
case R_386_32:
case R_386_RELATIVE: /* Don't care. */
+ case R_386_IRELATIVE:
// sym_addr was initialized to be zero above or relocation
// code below does not care about value of sym_addr.
// No need to do anything.
@@ -1500,7 +1448,7 @@
}
} else {
// We got a definition.
- sym_addr = static_cast<ElfW(Addr)>(s->st_value + lsi->load_bias);
+ sym_addr = lsi->resolve_symbol_address(s);
}
count_relocation(kRelocSymbol);
}
@@ -1549,11 +1497,7 @@
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
- if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
- set_has_ifuncs(true);
- } else {
- *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
- }
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
break;
case R_386_GLOB_DAT:
count_relocation(kRelocAbsolute);
@@ -1614,6 +1558,14 @@
reinterpret_cast<void*>(reloc), reinterpret_cast<void*>(base));
*reinterpret_cast<ElfW(Addr)*>(reloc) += base;
break;
+#if defined(__i386__)
+ case R_386_IRELATIVE:
+ count_relocation(kRelocRelative);
+ MARK(rel->r_offset);
+ TRACE_TYPE(RELO, "RELO IRELATIVE %p <- %p", reinterpret_cast<void*>(reloc), reinterpret_cast<void*>(base));
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = call_ifunc_resolver(base + *reinterpret_cast<ElfW(Addr)*>(reloc));
+ break;
+#endif
default:
DL_ERR("unknown reloc type %d @ %p (%zu)", type, rel, idx);
@@ -1671,7 +1623,7 @@
// FIXME: is this sufficient?
// For reference see NetBSD link loader
// http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup
- *got = reinterpret_cast<ElfW(Addr)*>(lsi->load_bias + s->st_value);
+ *got = reinterpret_cast<ElfW(Addr)*>(lsi->resolve_symbol_address(s));
}
}
return true;
@@ -1749,8 +1701,6 @@
// DT_INIT should be called before DT_INIT_ARRAY if both are present.
CallFunction("DT_INIT", init_func);
CallArray("DT_INIT_ARRAY", init_array, init_array_count, false);
-
- resolve_ifunc_symbols();
}
void soinfo::CallDestructors() {
@@ -1812,12 +1762,6 @@
}
}
-void soinfo::set_has_ifuncs(bool ifuncs) {
- if (has_min_version(1)) {
- has_ifuncs = ifuncs;
- }
-}
-
dev_t soinfo::get_st_dev() {
if (has_min_version(0)) {
return st_dev;
@@ -1834,14 +1778,6 @@
return 0;
}
-bool soinfo::get_has_ifuncs() {
- if (has_min_version(1)) {
- return has_ifuncs;
- }
-
- return false;
-}
-
// This is a return on get_children()/get_parents() if
// 'this->flags' does not have FLAG_NEW_SOINFO set.
static soinfo::soinfo_list_t g_empty_list;
@@ -1862,6 +1798,14 @@
return this->parents;
}
+ElfW(Addr) soinfo::resolve_symbol_address(ElfW(Sym)* s) {
+ if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+ return call_ifunc_resolver(s->st_value + load_bias);
+ }
+
+ return static_cast<ElfW(Addr)>(s->st_value + load_bias);
+}
+
/* Force any of the closed stdin, stdout and stderr to be associated with
/dev/null. */
static int nullify_closed_stdio() {
@@ -2168,44 +2112,32 @@
#endif
#if defined(USE_RELA)
- if (plt_rela != nullptr) {
- DEBUG("[ relocating %s plt ]\n", name);
- if (Relocate(plt_rela, plt_rela_count)) {
- return false;
- }
- }
if (rela != nullptr) {
- DEBUG("[ relocating %s ]\n", name);
+ DEBUG("[ relocating %s ]", name);
if (Relocate(rela, rela_count)) {
return false;
}
}
-#else
- if (plt_rel != nullptr) {
+ if (plt_rela != nullptr) {
DEBUG("[ relocating %s plt ]", name);
- if (Relocate(plt_rel, plt_rel_count)) {
+ if (Relocate(plt_rela, plt_rela_count)) {
return false;
}
}
+#else
if (rel != nullptr) {
DEBUG("[ relocating %s ]", name);
if (Relocate(rel, rel_count)) {
return false;
}
}
-#endif
-
- // if there are ifuncs, we need to do an additional relocation pass.
- // they cannot be resolved until the rest of the relocations are done
- // because we need to call the resolution function which may be waiting
- // on relocations.
- if(get_has_ifuncs()) {
-#if defined(__i386__)
- soinfo_ifunc_relocate(this, plt_rel, plt_rel_count);
-#elif defined(__x86_64__)
- soinfo_ifunc_relocate(this, plt_rela, plt_rela_count);
-#endif
+ if (plt_rel != nullptr) {
+ DEBUG("[ relocating %s plt ]", name);
+ if (Relocate(plt_rel, plt_rel_count)) {
+ return false;
+ }
}
+#endif
#if defined(__mips__)
if (!mips_relocate_got(this)) {