linker: add experimental support for SHT_RELR sections.
This change adds experimental support for SHT_RELR sections, proposed
here: https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
Definitions for the new ELF section type and dynamic array tags, as well
as the encoding used in the new section are all under discussion and are
subject to change. Use with caution!
Bug: None
Test: Built image for marlin, flashed on device, ran arm and
aarch64 binaries containing '.relr.dyn' sections.
Change-Id: I2953ae932d3c42ae394e71f8fa058013758a1778
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 317fdff..abcff2a 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -2595,6 +2595,35 @@
return true;
}
+// Process relocations in SHT_RELR section (experimental).
+// See the original proposal for details of the encoding:
+// - https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
+bool soinfo::relocate_relr() {
+ ElfW(Relr)* begin = relr_;
+ ElfW(Relr)* end = relr_ + relr_count_;
+
+ ElfW(Addr) offset = 0;
+ for (ElfW(Relr)* current = begin; current < end; ++current) {
+ ElfW(Addr) jump = ELFW(R_JUMP)(*current);
+ ElfW(Addr) bits = ELFW(R_BITS)(*current);
+ offset += jump * sizeof(ElfW(Addr));
+ if (jump == 0) {
+ ++current;
+ offset = *current;
+ }
+ ElfW(Addr) r_offset = offset;
+ for (; bits != 0; bits >>= 1) {
+ if ((bits&1) != 0) {
+ ElfW(Addr) reloc = static_cast<ElfW(Addr)>(r_offset + load_bias);
+ ElfW(Addr) addend = *reinterpret_cast<ElfW(Addr)*>(reloc);
+ *reinterpret_cast<ElfW(Addr)*>(reloc) = (load_bias + addend);
+ }
+ r_offset += sizeof(ElfW(Addr));
+ }
+ }
+ return true;
+}
+
#if !defined(__mips__)
#if defined(USE_RELA)
static ElfW(Addr) get_addend(ElfW(Rela)* rela, ElfW(Addr) reloc_addr __unused) {
@@ -3151,7 +3180,7 @@
}
break;
- // ignored (see DT_RELCOUNT comments for details)
+ // Ignored (see DT_RELCOUNT comments for details).
case DT_RELACOUNT:
break;
@@ -3212,6 +3241,25 @@
return false;
#endif
+ case DT_RELR:
+ relr_ = reinterpret_cast<ElfW(Relr)*>(load_bias + d->d_un.d_ptr);
+ break;
+
+ case DT_RELRSZ:
+ relr_count_ = d->d_un.d_val / sizeof(ElfW(Relr));
+ break;
+
+ case DT_RELRENT:
+ if (d->d_un.d_val != sizeof(ElfW(Relr))) {
+ DL_ERR("invalid DT_RELRENT: %zd", static_cast<size_t>(d->d_un.d_val));
+ return false;
+ }
+ break;
+
+ // Ignored (see DT_RELCOUNT comments for details).
+ case DT_RELRCOUNT:
+ break;
+
case DT_INIT:
init_func_ = reinterpret_cast<linker_ctor_function_t>(load_bias + d->d_un.d_ptr);
DEBUG("%s constructors (DT_INIT) found at %p", get_realpath(), init_func_);
@@ -3504,16 +3552,23 @@
}
}
+ if (relr_ != nullptr) {
+ DEBUG("[ relocating %s relr ]", get_realpath());
+ if (!relocate_relr()) {
+ return false;
+ }
+ }
+
#if defined(USE_RELA)
if (rela_ != nullptr) {
- DEBUG("[ relocating %s ]", get_realpath());
+ DEBUG("[ relocating %s rela ]", get_realpath());
if (!relocate(version_tracker,
plain_reloc_iterator(rela_, rela_count_), global_group, local_group)) {
return false;
}
}
if (plt_rela_ != nullptr) {
- DEBUG("[ relocating %s plt ]", get_realpath());
+ DEBUG("[ relocating %s plt rela ]", get_realpath());
if (!relocate(version_tracker,
plain_reloc_iterator(plt_rela_, plt_rela_count_), global_group, local_group)) {
return false;
@@ -3521,14 +3576,14 @@
}
#else
if (rel_ != nullptr) {
- DEBUG("[ relocating %s ]", get_realpath());
+ DEBUG("[ relocating %s rel ]", get_realpath());
if (!relocate(version_tracker,
plain_reloc_iterator(rel_, rel_count_), global_group, local_group)) {
return false;
}
}
if (plt_rel_ != nullptr) {
- DEBUG("[ relocating %s plt ]", get_realpath());
+ DEBUG("[ relocating %s plt rel ]", get_realpath());
if (!relocate(version_tracker,
plain_reloc_iterator(plt_rel_, plt_rel_count_), global_group, local_group)) {
return false;
diff --git a/linker/linker_soinfo.h b/linker/linker_soinfo.h
index 91118b0..cb607a9 100644
--- a/linker/linker_soinfo.h
+++ b/linker/linker_soinfo.h
@@ -62,7 +62,7 @@
// unset.
#define FLAG_NEW_SOINFO 0x40000000 // new soinfo format
-#define SOINFO_VERSION 3
+#define SOINFO_VERSION 4
typedef void (*linker_dtor_function_t)();
typedef void (*linker_ctor_function_t)(int, char**, char**);
@@ -309,6 +309,7 @@
template<typename ElfRelIteratorT>
bool relocate(const VersionTracker& version_tracker, ElfRelIteratorT&& rel_iterator,
const soinfo_list_t& global_group, const soinfo_list_t& local_group);
+ bool relocate_relr();
private:
// This part of the structure is only available
@@ -365,6 +366,10 @@
friend soinfo* get_libdl_info(const char* linker_path,
const soinfo& linker_si,
const link_map& linker_map);
+
+ // version >= 4
+ ElfW(Relr)* relr_;
+ size_t relr_count_;
};
// This function is used by dlvsym() to calculate hash of sym_ver