Added test for ifunc support in dynamic linker.
ifuncs now work in i386 and x86_64 when called in the same library as
well as in a different library.
Bug:6657325
Change-Id: Ic0c48b1b0a76cb90f36c20c79f68294cc3fd44a1
diff --git a/linker/linker.cpp b/linker/linker.cpp
index f8b35d7..b0f0e4d 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -476,6 +476,29 @@
return NULL;
}
+static void resolve_ifunc_symbols(soinfo* si) {
+
+ phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias);
+
+ TRACE_TYPE(IFUNC, "CHECKING FOR IFUNCS AND PERFORMING SYMBOL UPDATES");
+
+ for (size_t i = 0; i < si->nchain; ++i) {
+ ElfW(Sym)* s = &si->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 + si->base);
+ s->st_value = (ifunc_ptr() - si->base);
+ TRACE_TYPE(IFUNC, "NEW VALUE IS %p", (void*)s->st_value);
+ }
+ }
+ phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias);
+}
+
static unsigned elfhash(const char* _name) {
const unsigned char* name = reinterpret_cast<const unsigned char*>(_name);
unsigned h = 0, g;
@@ -790,6 +813,10 @@
return NULL;
}
+ // if the library has any ifuncs, we will need to resolve them so that dlsym
+ // can handle them properly
+ resolve_ifunc_symbols(si);
+
return si;
}
@@ -903,6 +930,53 @@
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, soinfo* needed[]) {
+ 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 = NULL;
+ sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
+ s = soinfo_do_lookup(si, sym_name, &lsi, needed);
+
+ 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();
+ }
+ }
+}
+#endif
+
+#if defined(__x86_64__)
+static void soinfo_ifunc_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo* needed[]) {
+ 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 = NULL;
+ sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
+ s = soinfo_do_lookup(si, sym_name, &lsi, needed);
+
+ 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)
static int soinfo_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo* needed[]) {
ElfW(Sym)* s;
@@ -1114,7 +1188,11 @@
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);
- *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
+ if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+ si->set_has_ifuncs(true);
+ } else {
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
+ }
break;
case R_X86_64_GLOB_DAT:
count_relocation(kRelocAbsolute);
@@ -1293,7 +1371,11 @@
count_relocation(kRelocAbsolute);
MARK(rel->r_offset);
TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
- *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
+ if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+ si->set_has_ifuncs(true);
+ } else {
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
+ }
break;
case R_386_GLOB_DAT:
count_relocation(kRelocAbsolute);
@@ -1553,6 +1635,14 @@
st_ino = ino;
}
+void soinfo::set_has_ifuncs(bool ifuncs) {
+ if ((this->flags & FLAG_NEW_SOINFO) == 0) {
+ return;
+ }
+
+ has_ifuncs = ifuncs;
+}
+
dev_t soinfo::get_st_dev() {
if ((this->flags & FLAG_NEW_SOINFO) == 0) {
return 0;
@@ -1569,6 +1659,14 @@
return st_ino;
}
+bool soinfo::get_has_ifuncs() {
+ if ((this->flags & FLAG_NEW_SOINFO) == 0) {
+ return false;
+ }
+
+ return has_ifuncs;
+}
+
// This is a return on get_children() in case
// 'this->flags' does not have FLAG_NEW_SOINFO set.
static soinfo::soinfo_list_t g_empty_list;
@@ -1953,6 +2051,18 @@
}
#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(si->get_has_ifuncs()) {
+#if defined(__i386__)
+ soinfo_ifunc_relocate(si, si->plt_rel, si->plt_rel_count, needed);
+#elif defined(__x86_64__)
+ soinfo_ifunc_relocate(si, si->plt_rela, si->plt_rela_count, needed);
+#endif
+ }
+
#if defined(__mips__)
if (!mips_relocate_got(si, needed)) {
return false;