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SE: Ignore FUTEX_PRIVATE_FLAG of sys_futex

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This patch ignores the FUTEX_PRIVATE_FLAG of the sys_futex system call
in SE mode.

With this patch, when sys_futex with the options FUTEX_WAIT_PRIVATE or
FUTEX_WAKE_PRIVATE is emulated, the FUTEX_PRIVATE_FLAG is ignored and
so their behaviours are the regular FUTEX_WAIT and FUTEX_WAKE.

Emulating FUTEX_WAIT_PRIVATE and FUTEX_WAKE_PRIVATE as if they were
non-private is safe from a functional point of view. The
FUTEX_PRIVATE_FLAG does not change the semantics of the futex, it's
just a mechanism to improve performance under certain circunstances
that can be ignored in SE mode.
This commit is contained in:
Lluc Alvarez 2012-09-21 04:51:18 -04:00
parent 9cd0c5ecc8
commit c8de765468
2 changed files with 3 additions and 1 deletions
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1
src/kern/linux/linux.hh
View file

@ -225,6 +225,7 @@ class Linux : public OperatingSystem
static const unsigned TGT_FUTEX_WAKE = 1; static const unsigned TGT_FUTEX_WAKE = 1;
static const unsigned TGT_EAGAIN = 11; static const unsigned TGT_EAGAIN = 11;
static const unsigned TGT_EWOULDBLOCK = TGT_EAGAIN; static const unsigned TGT_EWOULDBLOCK = TGT_EAGAIN;
static const unsigned TGT_FUTEX_PRIVATE_FLAG = 128;
}; // class Linux }; // class Linux

3
src/sim/syscall_emul.hh
View file

@ -359,6 +359,7 @@ futexFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
DPRINTF(SyscallVerbose, "In sys_futex: Address=%llx, op=%d, val=%d\n", DPRINTF(SyscallVerbose, "In sys_futex: Address=%llx, op=%d, val=%d\n",
uaddr, op, val); uaddr, op, val);
op &= ~OS::TGT_FUTEX_PRIVATE_FLAG;
if (op == OS::TGT_FUTEX_WAIT) { if (op == OS::TGT_FUTEX_WAIT) {
if (timeout != 0) { if (timeout != 0) {
@ -410,7 +411,7 @@ futexFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
"thread contexts\n", wokenUp); "thread contexts\n", wokenUp);
return wokenUp; return wokenUp;
} else { } else {
warn("sys_futex: op %d is not implemented, just returning..."); warn("sys_futex: op %d is not implemented, just returning...", op);
return 0; return 0;
} }