path: root/src/env/__init_tls.c
diff options
authorRich Felker <>2015-03-06 13:27:08 -0500
committerRich Felker <>2015-03-06 13:27:08 -0500
commitbd67959f3ad5049c35af0a0e2f8f1a1e60577a49 (patch)
treee902b7ed8e160789cfc372d25dfd6cbaa0e1492c /src/env/__init_tls.c
parent2b42c8cb37a3ef115bd04de8637078e43cd72f37 (diff)
fix over-alignment of TLS, insufficient builtin TLS on 64-bit archs
a conservative estimate of 4*sizeof(size_t) was used as the minimum alignment for thread-local storage, despite the only requirements being alignment suitable for struct pthread and void* (which struct pthread already contains). additional alignment required by the application or libraries is encoded in their headers and is already applied. over-alignment prevented the builtin_tls array from ever being used in dynamic-linked programs on 64-bit archs, thereby requiring allocation at startup even in programs with no TLS of their own.
Diffstat (limited to 'src/env/__init_tls.c')
1 files changed, 8 insertions, 2 deletions
diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
index ddc2a736..b0dad429 100644
--- a/src/env/__init_tls.c
+++ b/src/env/__init_tls.c
@@ -2,6 +2,7 @@
#include <limits.h>
#include <sys/mman.h>
#include <string.h>
+#include <stddef.h>
#include "pthread_impl.h"
#include "libc.h"
#include "atomic.h"
@@ -22,7 +23,12 @@ int __init_tp(void *p)
#ifndef SHARED
-static long long builtin_tls[(sizeof(struct pthread) + 64)/sizeof(long long)];
+static struct builtin_tls {
+ char c;
+ struct pthread pt;
+ void *space[16];
+} builtin_tls[1];
+#define MIN_TLS_ALIGN offsetof(struct builtin_tls, pt)
struct tls_image {
void *image;
@@ -86,7 +92,7 @@ void __init_tls(size_t *aux)
T.size += (-T.size - (uintptr_t)T.image) & (T.align-1);
- if (T.align < 4*sizeof(size_t)) T.align = 4*sizeof(size_t);
+ if (T.align < MIN_TLS_ALIGN) T.align = MIN_TLS_ALIGN;
libc.tls_size = 2*sizeof(void *)+T.size+T.align+sizeof(struct pthread);