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author | Florian Weimer <fweimer@redhat.com> | 2021-12-09 17:57:11 +0100 |
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committer | Florian Weimer <fweimer@redhat.com> | 2021-12-09 23:47:49 +0100 |
commit | 627f5ede70d70c77bdaf857db07404e8bf7f60af (patch) | |
tree | e01587b1f37c74a0d8eff0ef7e903969d9ba4b80 /elf/dl-tls.c | |
parent | a41c8e92350e744a4bc639df5025153d05263e7f (diff) | |
download | glibc-627f5ede70d70c77bdaf857db07404e8bf7f60af.tar.gz glibc-627f5ede70d70c77bdaf857db07404e8bf7f60af.tar.xz glibc-627f5ede70d70c77bdaf857db07404e8bf7f60af.zip |
Remove TLS_TCB_ALIGN and TLS_INIT_TCB_ALIGN
TLS_INIT_TCB_ALIGN is not actually used. TLS_TCB_ALIGN was likely introduced to support a configuration where the thread pointer has not the same alignment as THREAD_SELF. Only ia64 seems to use that, but for the stack/pointer guard, not for storing tcbhead_t. Some ports use TLS_TCB_OFFSET and TLS_PRE_TCB_SIZE to shift the thread pointer, potentially landing in a different residue class modulo the alignment, but the changes should not impact that. In general, given that TLS variables have their own alignment requirements, having different alignment for the (unshifted) thread pointer and struct pthread would potentially result in dynamic offsets, leading to more complexity. hppa had different values before: __alignof__ (tcbhead_t), which seems to be 4, and __alignof__ (struct pthread), which was 8 (old default) and is now 32. However, it defines THREAD_SELF as: /* Return the thread descriptor for the current thread. */ # define THREAD_SELF \ ({ struct pthread *__self; \ __self = __get_cr27(); \ __self - 1; \ }) So the thread pointer points after struct pthread (hence __self - 1), and they have to have the same alignment on hppa as well. Similarly, on ia64, the definitions were different. We have: # define TLS_PRE_TCB_SIZE \ (sizeof (struct pthread) \ + (PTHREAD_STRUCT_END_PADDING < 2 * sizeof (uintptr_t) \ ? ((2 * sizeof (uintptr_t) + __alignof__ (struct pthread) - 1) \ & ~(__alignof__ (struct pthread) - 1)) \ : 0)) # define THREAD_SELF \ ((struct pthread *) ((char *) __thread_self - TLS_PRE_TCB_SIZE)) And TLS_PRE_TCB_SIZE is a multiple of the struct pthread alignment (confirmed by the new _Static_assert in sysdeps/ia64/libc-tls.c). On m68k, we have a larger gap between tcbhead_t and struct pthread. But as far as I can tell, the port is fine with that. The definition of TCB_OFFSET is sufficient to handle the shifted TCB scenario. This fixes commit 23c77f60181eb549f11ec2f913b4270af29eee38 ("nptl: Increase default TCB alignment to 32"). Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Diffstat (limited to 'elf/dl-tls.c')
-rw-r--r-- | elf/dl-tls.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/elf/dl-tls.c b/elf/dl-tls.c index 9260d2d696..273f60f233 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -219,7 +219,7 @@ _dl_count_modids (void) void _dl_determine_tlsoffset (void) { - size_t max_align = TLS_TCB_ALIGN; + size_t max_align = TCB_ALIGNMENT; size_t freetop = 0; size_t freebottom = 0; @@ -350,7 +350,7 @@ _dl_determine_tlsoffset (void) GL(dl_tls_static_used) = offset; GLRO (dl_tls_static_size) = roundup (offset + GLRO(dl_tls_static_surplus), - TLS_TCB_ALIGN); + TCB_ALIGNMENT); #else # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined" #endif |