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x86: Fix THREAD_SELF definition to avoid ld.so crash (bug 27004)

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The previous definition of THREAD_SELF did not tell the compiler
that %fs (or %gs) usage is invalid for the !DL_LOOKUP_GSCOPE_LOCK
case in _dl_lookup_symbol_x.  As a result, ld.so could try to use the
TCB before it was initialized.

As the comment in tls.h explains, asm volatile is undesirable here.
Using the __seg_fs (or __seg_gs) namespace does not interfere with
optimization, and expresses that THREAD_SELF is potentially trapping.
This commit is contained in:
Jakub Jelinek 2020-12-03 13:33:44 +01:00 committed by Florian Weimer
parent 7c33111697
commit 1d9cbb9608
2 changed files with 12 additions and 2 deletions
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7
sysdeps/i386/nptl/tls.h
View File

@ -234,11 +234,16 @@ tls_fill_user_desc (union user_desc_init *desc,
assignments like
pthread_descr self = thread_self();
do not get optimized away. */
# define THREAD_SELF \
# if __GNUC_PREREQ (6, 0)
# define THREAD_SELF \
(*(struct pthread *__seg_gs *) offsetof (struct pthread, header.self))
# else
# define THREAD_SELF \
({ struct pthread *__self; \
asm ("movl %%gs:%c1,%0" : "=r" (__self) \
: "i" (offsetof (struct pthread, header.self))); \
__self;})
# endif
/* Magic for libthread_db to know how to do THREAD_SELF. */
# define DB_THREAD_SELF \

7
sysdeps/x86_64/nptl/tls.h
View File

@ -180,11 +180,16 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
assignments like
pthread_descr self = thread_self();
do not get optimized away. */
# define THREAD_SELF \
# if __GNUC_PREREQ (6, 0)
# define THREAD_SELF \
(*(struct pthread *__seg_fs *) offsetof (struct pthread, header.self))
# else
# define THREAD_SELF \
({ struct pthread *__self; \
asm ("mov %%fs:%c1,%0" : "=r" (__self) \
: "i" (offsetof (struct pthread, header.self))); \
__self;})
# endif
/* Magic for libthread_db to know how to do THREAD_SELF. */
# define DB_THREAD_SELF_INCLUDE <sys/reg.h> /* For the FS constant. */