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x86_64: Remove wrong THREAD_ATOMIC_* macros 

The x86 defines optimized THREAD_ATOMIC_* macros where reference always
the current thread instead of the one indicated by input 'descr' argument.
It work as long the input is the self thread pointer, however it generates
wrong code if the semantic is to set a bit atomicialy from another thread.

This is not an issue for current GLIBC usage, however the new cancellation
code expects that some synchronization code to atomically set bits from
different threads.

The generic code generates an additional load to reference to TLS segment,
for instance the code:

  THREAD_ATOMIC_BIT_SET (THREAD_SELF, cancelhandling, CANCELED_BIT);

Compiles to:

  lock;orl $4, %fs:776

Where with patch changes it now compiles to:

  mov %fs:16,%rax
  lock;orl $4, 776(%rax)

If some usage indeed proves to be a hotspot we can add an extra macro
with a more descriptive name (THREAD_ATOMIC_BIT_SET_SELF for instance)
where x86_64 might optimize it.

Checked on x86_64-linux-gnu.

	* sysdeps/x86_64/nptl/tls.h (THREAD_ATOMIC_CMPXCHG_VAL,
	THREAD_ATOMIC_AND, THREAD_ATOMIC_BIT_SET): Remove macros.
This commit is contained in:
Adhemerval Zanella 2018-05-09 10:32:25 -03:00
parent d0d7f85f66
commit 85c828a462
2 changed files with 3 additions and 37 deletions
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3
ChangeLog
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@ -1,5 +1,8 @@
2019-01-03 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* sysdeps/x86_64/nptl/tls.h (THREAD_ATOMIC_CMPXCHG_VAL,
THREAD_ATOMIC_AND, THREAD_ATOMIC_BIT_SET): Remove macros.
* debug/tst-backtrace5.c (handle_signal): Avoid cancellable wrappers
in backtrace analysis.
* nptl/tst-cancel4.c (tf_write): Handle cancelled syscall with

37
sysdeps/x86_64/nptl/tls.h
View File

@ -306,43 +306,6 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
}})
/* Atomic compare and exchange on TLS, returning old value. */
# define THREAD_ATOMIC_CMPXCHG_VAL(descr, member, newval, oldval) \
({ __typeof (descr->member) __ret; \
__typeof (oldval) __old = (oldval); \
if (sizeof (descr->member) == 4) \
asm volatile (LOCK_PREFIX "cmpxchgl %2, %%fs:%P3" \
: "=a" (__ret) \
: "0" (__old), "r" (newval), \
"i" (offsetof (struct pthread, member))); \
else \
/* Not necessary for other sizes in the moment. */ \
abort (); \
__ret; })
/* Atomic logical and. */
# define THREAD_ATOMIC_AND(descr, member, val) \
(void) ({ if (sizeof ((descr)->member) == 4) \
asm volatile (LOCK_PREFIX "andl %1, %%fs:%P0" \
:: "i" (offsetof (struct pthread, member)), \
"ir" (val)); \
else \
/* Not necessary for other sizes in the moment. */ \
abort (); })
/* Atomic set bit. */
# define THREAD_ATOMIC_BIT_SET(descr, member, bit) \
(void) ({ if (sizeof ((descr)->member) == 4) \
asm volatile (LOCK_PREFIX "orl %1, %%fs:%P0" \
:: "i" (offsetof (struct pthread, member)), \
"ir" (1 << (bit))); \
else \
/* Not necessary for other sizes in the moment. */ \
abort (); })
/* Set the stack guard field in TCB head. */
# define THREAD_SET_STACK_GUARD(value) \
THREAD_SETMEM (THREAD_SELF, header.stack_guard, value)