From c8de7654682dd8f5efa920f79d6041f2cac2fbeb Mon Sep 17 00:00:00 2001 From: Lluc Alvarez Date: Fri, 21 Sep 2012 04:51:18 -0400 Subject: [PATCH] SE: Ignore FUTEX_PRIVATE_FLAG of sys_futex 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. --- src/kern/linux/linux.hh | 1 + src/sim/syscall_emul.hh | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/src/kern/linux/linux.hh b/src/kern/linux/linux.hh index 1d52ff323..1fcd80444 100644 --- a/src/kern/linux/linux.hh +++ b/src/kern/linux/linux.hh @@ -225,6 +225,7 @@ class Linux : public OperatingSystem static const unsigned TGT_FUTEX_WAKE = 1; static const unsigned TGT_EAGAIN = 11; static const unsigned TGT_EWOULDBLOCK = TGT_EAGAIN; + static const unsigned TGT_FUTEX_PRIVATE_FLAG = 128; }; // class Linux diff --git a/src/sim/syscall_emul.hh b/src/sim/syscall_emul.hh index aec159838..e98e771d5 100644 --- a/src/sim/syscall_emul.hh +++ b/src/sim/syscall_emul.hh @@ -359,6 +359,7 @@ futexFunc(SyscallDesc *desc, int callnum, LiveProcess *process, DPRINTF(SyscallVerbose, "In sys_futex: Address=%llx, op=%d, val=%d\n", uaddr, op, val); + op &= ~OS::TGT_FUTEX_PRIVATE_FLAG; if (op == OS::TGT_FUTEX_WAIT) { if (timeout != 0) { @@ -410,7 +411,7 @@ futexFunc(SyscallDesc *desc, int callnum, LiveProcess *process, "thread contexts\n", wokenUp); return wokenUp; } else { - warn("sys_futex: op %d is not implemented, just returning..."); + warn("sys_futex: op %d is not implemented, just returning...", op); return 0; }