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kern,sim: implement FUTEX_WAKE_OP

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This patch implements FUTEX_WAKE_OP operation in the futex syscall.
Below is its description:

int futex(int *uaddr, int futex_op, int val,
          const struct timespec *timeout,
          int *uaddr2, int val3);

This operation was added to support some user-space use cases where more
than one futex must be handled at the same time.  The most notable
example is the implementation of pthread_cond_signal(3), which requires
operations on two futexes, the one used to implement the mutex and the
one used in the implementation of the wait queue associated with the
condition variable.  FUTEX_WAKE_OP allows such cases to be implemented
without leading to high rates of contention and context switching.

Reference: http://man7.org/linux/man-pages/man2/futex.2.html

Change-Id: I215f3c2a7bdc6374e5dfe06ee721c76933a10f2d
Reviewed-on: https://gem5-review.googlesource.com/c/9630
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
This commit is contained in:
Moyang Wang
2018-04-02 16:23:13 -04:00
committed by Tuan Ta
parent 758b62cfb2
commit 165a7dab55
2 changed files with 87 additions and 0 deletions
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16
src/kern/linux/linux.hh
View File

@@ -243,12 +243,28 @@ class Linux : public OperatingSystem
static const unsigned TGT_FUTEX_WAKE = 1;
static const unsigned TGT_FUTEX_REQUEUE = 3;
static const unsigned TGT_FUTEX_CMP_REQUEUE = 4;
static const unsigned TGT_FUTEX_WAKE_OP = 5;
static const unsigned TGT_FUTEX_WAIT_BITSET = 9;
static const unsigned TGT_FUTEX_WAKE_BITSET = 10;
static const unsigned TGT_EAGAIN = 11;
static const unsigned TGT_EWOULDBLOCK = TGT_EAGAIN;
static const unsigned TGT_FUTEX_PRIVATE_FLAG = 128;
static const unsigned TGT_FUTEX_CLOCK_REALTIME_FLAG = 256;
// op field of futex_wake_op operation
static const unsigned TGT_FUTEX_OP_SET = 0; // uaddr2 = oparg;
static const unsigned TGT_FUTEX_OP_ADD = 1; // uaddr2 += oparg;
static const unsigned TGT_FUTEX_OP_OR = 2; // uaddr2 |= oparg;
static const unsigned TGT_FUTEX_OP_ANDN = 3; // uaddr2 &= ~oparg;
static const unsigned TGT_FUTEX_OP_XOR = 4; // uaddr2 ^= oparg;
// Use (1 << oparg) as operand
static const unsigned TGT_FUTEX_OP_ARG_SHIFT = 8;
// cmp field of futex_wake_op operation
static const unsigned TGT_FUTEX_OP_CMP_EQ = 0;
static const unsigned TGT_FUTEX_OP_CMP_NE = 1;
static const unsigned TGT_FUTEX_OP_CMP_LT = 2;
static const unsigned TGT_FUTEX_OP_CMP_LE = 3;
static const unsigned TGT_FUTEX_OP_CMP_GT = 4;
static const unsigned TGT_FUTEX_OP_CMP_GE = 5;
// for *at syscalls
static const int TGT_AT_FDCWD = -100;

71
src/sim/syscall_emul.hh
View File

@@ -455,6 +455,77 @@ futexFunc(SyscallDesc *desc, int callnum, Process *process,
if (OS::TGT_FUTEX_CMP_REQUEUE && val3 != mem_val)
return -OS::TGT_EWOULDBLOCK;
return futex_map.requeue(uaddr, process->tgid(), val, timeout, uaddr2);
} else if (OS::TGT_FUTEX_WAKE_OP == op) {
/*
* The FUTEX_WAKE_OP operation is equivalent to executing the
* following code atomically and totally ordered with respect to
* other futex operations on any of the two supplied futex words:
*
* int oldval = *(int *) addr2;
* *(int *) addr2 = oldval op oparg;
* futex(addr1, FUTEX_WAKE, val, 0, 0, 0);
* if (oldval cmp cmparg)
* futex(addr2, FUTEX_WAKE, val2, 0, 0, 0);
*
* (op, oparg, cmp, cmparg are encoded in val3)
*
* +---+---+-----------+-----------+
* |op |cmp| oparg | cmparg |
* +---+---+-----------+-----------+
* 4 4 12 12 <== # of bits
*
* reference: http://man7.org/linux/man-pages/man2/futex.2.html
*
*/
// get value from simulated-space
BufferArg buf(uaddr2, sizeof(int));
buf.copyIn(tc->getMemProxy());
int oldval = *(int*)buf.bufferPtr();
int newval = oldval;
// extract op, oparg, cmp, cmparg from val3
int wake_cmparg = val3 & 0xfff;
int wake_oparg = (val3 & 0xfff000) >> 12;
int wake_cmp = (val3 & 0xf000000) >> 24;
int wake_op = (val3 & 0xf0000000) >> 28;
if ((wake_op & OS::TGT_FUTEX_OP_ARG_SHIFT) >> 3 == 1)
wake_oparg = (1 << wake_oparg);
wake_op &= ~OS::TGT_FUTEX_OP_ARG_SHIFT;
// perform operation on the value of the second futex
if (wake_op == OS::TGT_FUTEX_OP_SET)
newval = wake_oparg;
else if (wake_op == OS::TGT_FUTEX_OP_ADD)
newval += wake_oparg;
else if (wake_op == OS::TGT_FUTEX_OP_OR)
newval |= wake_oparg;
else if (wake_op == OS::TGT_FUTEX_OP_ANDN)
newval &= ~wake_oparg;
else if (wake_op == OS::TGT_FUTEX_OP_XOR)
newval ^= wake_oparg;
// copy updated value back to simulated-space
*(int*)buf.bufferPtr() = newval;
buf.copyOut(tc->getMemProxy());
// perform the first wake-up
int woken1 = futex_map.wakeup(uaddr, process->tgid(), val);
int woken2 = 0;
// calculate the condition of the second wake-up
bool is_wake2 = false;
if (wake_cmp == OS::TGT_FUTEX_OP_CMP_EQ)
is_wake2 = oldval == wake_cmparg;
else if (wake_cmp == OS::TGT_FUTEX_OP_CMP_NE)
is_wake2 = oldval != wake_cmparg;
else if (wake_cmp == OS::TGT_FUTEX_OP_CMP_LT)
is_wake2 = oldval < wake_cmparg;
else if (wake_cmp == OS::TGT_FUTEX_OP_CMP_LE)
is_wake2 = oldval <= wake_cmparg;
else if (wake_cmp == OS::TGT_FUTEX_OP_CMP_GT)
is_wake2 = oldval > wake_cmparg;
else if (wake_cmp == OS::TGT_FUTEX_OP_CMP_GE)
is_wake2 = oldval >= wake_cmparg;
// perform the second wake-up
if (is_wake2)
woken2 = futex_map.wakeup(uaddr2, process->tgid(), timeout);
return woken1 + woken2;
}
warn("futex: op %d not implemented; ignoring.", op);
return -ENOSYS;