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authorRich Felker <dalias@aerifal.cx>2018-10-16 13:36:51 -0400
committerRich Felker <dalias@aerifal.cx>2018-10-16 13:50:28 -0400
commit1c84c99913bf1cd47b866ed31e665848a0da84a2 (patch)
tree03d3817133ba8655b474863381211ccd3ed11e34 /ldso/dynlink.c
parent2085378a4fad15f65686d78f52dc6fb5362bdf20 (diff)
downloadmusl-1c84c99913bf1cd47b866ed31e665848a0da84a2.tar.gz
add new stage 2b to dynamic linker bootstrap for thread pointer
commit a603a75a72bb469c6be4963ed1b55fabe675fe15 removed attribute const from __errno_location and pthread_self, and the same reasoning forced arch definitions of __pthread_self to use volatile asm, significantly impacting code generation and imposing manual caching of pointers where the impact might be noticable. reorder the thread pointer setup and place it across a strong barrier (symbolic function lookup) so that there is no assumed ordering between the initialization and the accesses to the thread pointer in stage 3.
Diffstat (limited to 'ldso/dynlink.c')
-rw-r--r--ldso/dynlink.c33
1 files changed, 23 insertions, 10 deletions
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index c2447bc9..ec921dfd 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1453,9 +1453,31 @@ hidden void __dls2(unsigned char *base, size_t *sp)
ldso.relocated = 0;
- /* Call dynamic linker stage-3, __dls3, looking it up
+ /* Call dynamic linker stage-2b, __dls2b, looking it up
* symbolically as a barrier against moving the address
* load across the above relocation processing. */
+ struct symdef dls2b_def = find_sym(&ldso, "__dls2b", 0);
+ if (DL_FDPIC) ((stage3_func)&ldso.funcdescs[dls2b_def.sym-ldso.syms])(sp);
+ else ((stage3_func)laddr(&ldso, dls2b_def.sym->st_value))(sp);
+}
+
+/* Stage 2b sets up a valid thread pointer, which requires relocations
+ * completed in stage 2, and on which stage 3 is permitted to depend.
+ * This is done as a separate stage, with symbolic lookup as a barrier,
+ * so that loads of the thread pointer and &errno can be pure/const and
+ * thereby hoistable. */
+
+_Noreturn void __dls2b(size_t *sp)
+{
+ /* Setup early thread pointer in builtin_tls for ldso/libc itself to
+ * use during dynamic linking. If possible it will also serve as the
+ * thread pointer at runtime. */
+ libc.tls_size = sizeof builtin_tls;
+ libc.tls_align = tls_align;
+ if (__init_tp(__copy_tls((void *)builtin_tls)) < 0) {
+ a_crash();
+ }
+
struct symdef dls3_def = find_sym(&ldso, "__dls3", 0);
if (DL_FDPIC) ((stage3_func)&ldso.funcdescs[dls3_def.sym-ldso.syms])(sp);
else ((stage3_func)laddr(&ldso, dls3_def.sym->st_value))(sp);
@@ -1490,15 +1512,6 @@ _Noreturn void __dls3(size_t *sp)
libc.secure = ((aux[0]&0x7800)!=0x7800 || aux[AT_UID]!=aux[AT_EUID]
|| aux[AT_GID]!=aux[AT_EGID] || aux[AT_SECURE]);
- /* Setup early thread pointer in builtin_tls for ldso/libc itself to
- * use during dynamic linking. If possible it will also serve as the
- * thread pointer at runtime. */
- libc.tls_size = sizeof builtin_tls;
- libc.tls_align = tls_align;
- if (__init_tp(__copy_tls((void *)builtin_tls)) < 0) {
- a_crash();
- }
-
/* Only trust user/env if kernel says we're not suid/sgid */
if (!libc.secure) {
env_path = getenv("LD_LIBRARY_PATH");