Implement arm64 TLSDESC
Each TLSDESC relocation relocates a 2-word descriptor in the GOT that
contains:
- the address of a TLS resolver function
- an argument to pass (indirectly) to the resolver function
(Specifically, the address of the 2-word descriptor is passed to the
resolver.)
The loader resolves R_GENERIC_TLSDESC relocations using one of three
resolver functions that it defines:
- tlsdesc_resolver_static
- tlsdesc_resolver_dynamic
- tlsdesc_resolver_unresolved_weak
The resolver functions are written in assembly because they have a
restrictive calling convention. They're only allowed to modify x0 and
(apparently) the condition codes.
For a relocation to memory in static TLS (i.e. the executable or an solib
loaded initially), the loader uses a simple resolver function,
tlsdesc_resolver_static, that returns the static offset it receives from
the loader.
For relocations to dynamic TLS memory (i.e. memory in a dlopen'ed solib),
the loader uses tlsdesc_resolver_dynamic, which allocates TLS memory on
demand. It inlines the fast path of __tls_get_addr, then falls back to
__tls_get_addr when it needs to allocate memory. The loader handles these
dynamic TLS relocations in two passes:
- In the first pass, it allocates a table of TlsDynamicResolverArg
objects, one per dynamic TLSDESC relocation.
- In the second pass, once the table is finalized, it writes the
addresses of the TlsDynamicResolverArg objects into the TLSDESC
relocations.
tlsdesc_resolver_unresolved_weak returns a negated thread pointer so that
taking the address of an unresolved weak TLS symbols produces NULL.
The loader handles R_GENERIC_TLSDESC in a target-independent way, but
only for arm64, because Bionic has only implemented the resolver functions
for arm64.
Bug: http://b/78026329
Test: bionic unit tests
Test: check that backtrace works inside a resolver function and inside
__tls_get_addr called from a resolver
(gdbclient.py, b __tls_get_addr, bt)
Change-Id: I752e59ff986292449892c449dad2546e6f0ff7b6
diff --git a/linker/linker_tls.h b/linker/linker_tls.h
index fbb1dcf..87e1f0d 100644
--- a/linker/linker_tls.h
+++ b/linker/linker_tls.h
@@ -30,6 +30,8 @@
#include <stdlib.h>
+#include "private/bionic_elf_tls.h"
+
struct TlsModule;
struct soinfo;
@@ -40,3 +42,24 @@
void unregister_soinfo_tls(soinfo* si);
const TlsModule& get_tls_module(size_t module_id);
+
+typedef size_t TlsDescResolverFunc(size_t);
+
+struct TlsDescriptor {
+#if defined(__arm__)
+ size_t arg;
+ TlsDescResolverFunc* func;
+#else
+ TlsDescResolverFunc* func;
+ size_t arg;
+#endif
+};
+
+struct TlsDynamicResolverArg {
+ size_t generation;
+ TlsIndex index;
+};
+
+__LIBC_HIDDEN__ extern "C" size_t tlsdesc_resolver_static(size_t);
+__LIBC_HIDDEN__ extern "C" size_t tlsdesc_resolver_dynamic(size_t);
+__LIBC_HIDDEN__ extern "C" size_t tlsdesc_resolver_unresolved_weak(size_t);