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fix: broken futex syscall when FUTEX_WAIT is used

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This commit is contained in:
Yibo Yan
2025-12-22 12:23:01 +00:00
parent ebe76e26b0
commit 92bf909d95
2 changed files with 31 additions and 7 deletions
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13
src/Makefile
View File

@@ -49,13 +49,24 @@
#
# INTERCEPT_SYSCALL
# - (On GNU/Linux only) intercept glibc's syscall() for known relevant syscalls.
# If enabled, this currently only works to divert the getrandom syscall.
# If enabled, this currently only works a few types of syscalls,
# including FUTEX (see below), clock_gettime, etc.
#
# - note that on unusual architectures, if INTERCEPT_SYSCALL is set, you may
# need to explicitly define variadic_promotion_t (e.g. by putting
# -Dvariadic_promotion_t=int into CFLAGS). See src/faketime_common.h for
# more info.
#
# INTERCEPT_FUTEX
# - (On GNU/Linux only) intercept glibc's syscall() for relevant FUTEX syscalls.
# If enabled, FUTEX syscalls will be intercepted and translated correspondingly.
# - when FUTEX_WAIT_BITSET (with absolute deadline) is set, the deadline will
# be adjusted based on the faketime.
# - when FUTEX_WAKE (with relative deadline) is set, the deadline will be
# adjusted based on the time rate alone.
# - for other FUTEX operations, no adjustment is made for now.
#
#
# FAKE_STATELESS
# - Remove support for any functionality that requires sharing state across
# threads of a process, or different processes. This decreases the risk of

25
src/libfaketime.c
View File

@@ -4445,12 +4445,13 @@ long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t v
goto futex_fallback;
}
// if ((futex_op & FUTEX_CMD_MASK) == FUTEX_WAIT_BITSET) {
if (1) {
clockid_t clk_id = CLOCK_MONOTONIC;
if (futex_op & FUTEX_CLOCK_REALTIME)
clk_id = CLOCK_REALTIME;
int futex_cmd = futex_op & FUTEX_CMD_MASK;
clockid_t clk_id = CLOCK_MONOTONIC;
if (futex_op & FUTEX_CLOCK_REALTIME)
clk_id = CLOCK_REALTIME;
if (futex_cmd == FUTEX_WAIT_BITSET) {
// FUTEX_WAIT_BITSET uses absolute timeout
struct timespec real_tp, fake_tp;
DONT_FAKE_TIME((*real_clock_gettime)(clk_id, &real_tp));
@@ -4513,8 +4514,20 @@ long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t v
}
}
return 0;
} else if (futex_cmd == FUTEX_WAIT) {
// FUTEX_WAIT uses relative timeout - scale by time rate
struct timespec adjusted_timeout;
if (user_rate_set && !dont_fake && ((clk_id == CLOCK_REALTIME) || (clk_id == CLOCK_MONOTONIC))) {
timespecmul(timeout, 1.0 / user_rate, &adjusted_timeout);
} else {
adjusted_timeout = *timeout;
}
return real_syscall(number, uaddr, futex_op, val, &adjusted_timeout, uaddr2, val3);
} else {
return real_syscall(number, uaddr, futex_op, val, timeout, uaddr2, val3);
// Other futex operations - pass through unchanged
goto futex_fallback;
}
futex_fallback: