Merge pull request #527 from totoroyyb/master

fix: broken futex syscall when FUTEX_WAIT is used

Author: wolfcw

src/Makefile

@@ -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

src/libfaketime.c

@@ -4439,18 +4439,34 @@ pid_t getpid() {
 
 #ifdef INTERCEPT_SYSCALL
 #ifdef INTERCEPT_FUTEX
-long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t val, struct timespec* timeout, uint32_t* uaddr2, uint32_t val3) {
+static inline long make_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t val, struct timespec* timeout, uint32_t* uaddr2, uint32_t val3) { 
   if (timeout == NULL) {
     // not timeout related, just call the real syscall
+    return real_syscall(number, uaddr, futex_op, val, timeout, uaddr2, val3);
+  }
+  if (timeout->tv_sec < 0) {
+    // fprintf(stderr, "libfaketime: invalid timeout.tv_sec < 0\n");
+    timeout->tv_sec = 0;
+  }
+  if (timeout->tv_nsec < 0) {
+    // fprintf(stderr, "libfaketime: invalid timeout.tv_nsec < 0\n");
+    timeout->tv_nsec = 0;
+  }
+  return real_syscall(number, uaddr, futex_op, val, timeout, uaddr2, val3);
+}
+
+static inline long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t val, struct timespec* timeout, uint32_t* uaddr2, uint32_t val3) {
+  if (timeout == NULL) {
     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));
@@ -4463,9 +4479,7 @@ long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t v
     struct timespec adjusted_timeout, time_diff;
     timespecsub(&fake_tp, &real_tp, &time_diff);
     timespecsub(timeout, &time_diff, &adjusted_timeout);
-    // fprintf(stdout, "libfaketime: adjusted timeout: %ld.%09ld\n", adjusted_timeout.tv_sec, adjusted_timeout.tv_nsec);
-    long result;
-    result = real_syscall(number, uaddr, futex_op, val, &adjusted_timeout, uaddr2, val3);
+    long result = make_futex_syscall(number, uaddr, futex_op, val, &adjusted_timeout, uaddr2, val3);
     if (result != 0) {
       return result;
     }
@@ -4498,11 +4512,8 @@ long handle_futex_syscall(long number, uint32_t* uaddr, int futex_op, uint32_t v
       struct timespec real_timeout;
       timespecadd(&real_now, &wait_time, &real_timeout);
 
-      // fprintf(stdout, "libfaketime: recalculated real timeout: %ld.%09ld\n",
-      //         real_timeout.tv_sec, real_timeout.tv_nsec);
-
       // Call the real syscall with the recalculated timeout
-      result = real_syscall(number, uaddr, futex_op, val, &real_timeout, uaddr2, val3);
+      result = make_futex_syscall(number, uaddr, futex_op, val, &real_timeout, uaddr2, val3);
       if (result != 0) {
         return result;
       }
@@ -4513,12 +4524,24 @@ 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 make_futex_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:
-    return real_syscall(number, uaddr, futex_op, val, timeout, uaddr2, val3);
+    return make_futex_syscall(number, uaddr, futex_op, val, timeout, uaddr2, val3);
 }
 #endif