Emulate clock, times, and getrusage using the monotonic clock.

Upcoming WASI snapshots omit the `PROCESS_CPUTIME` clock, since WASI has
no inherent concept of processes, and since implementations which don't
use a process for each instance don't have a way to implement it
efficiently.

However, `clock`, `times`, and `getrusage` are useful functions, so
provide optional emulated version of them, using the `MONOTONIC` clock.
This means these implementations will measure not just the program's
own CPU time, but also time spent suspended while other programs are
running.

Due to this difference in behavior, put these implementations behind
a flag. Users must pass `-D_WASI_EMULATED_PROCESS_CLOCK` and link with
`-lwasi-emulated-process-clocks` to enable them.

Makefile

@@ -54,6 +54,8 @@ LIBC_BOTTOM_HALF_ALL_SOURCES := $(LIBC_BOTTOM_HALF_ALL_SOURCES) $(LIBC_BOTTOM_HA
 
 LIBWASI_EMULATED_MMAN_SOURCES = \
     $(shell find $(LIBC_BOTTOM_HALF_DIR)/mman -name \*.c)
+LIBWASI_EMULATED_PROCESS_CLOCKS_SOURCES = \
+    $(shell find $(LIBC_BOTTOM_HALF_DIR)/clocks -name \*.c)
 LIBWASI_EMULATED_SIGNAL_SOURCES = \
     $(shell find $(LIBC_BOTTOM_HALF_DIR)/signal -name \*.c)
 LIBWASI_EMULATED_SIGNAL_MUSL_SOURCES = \
@@ -229,6 +231,7 @@ MUSL_PRINTSCAN_OBJS = $(call objs,$(MUSL_PRINTSCAN_SOURCES))
 MUSL_PRINTSCAN_LONG_DOUBLE_OBJS = $(patsubst %.o,%.long-double.o,$(MUSL_PRINTSCAN_OBJS))
 MUSL_PRINTSCAN_NO_FLOATING_POINT_OBJS = $(patsubst %.o,%.no-floating-point.o,$(MUSL_PRINTSCAN_OBJS))
 LIBWASI_EMULATED_MMAN_OBJS = $(call objs,$(LIBWASI_EMULATED_MMAN_SOURCES))
+LIBWASI_EMULATED_PROCESS_CLOCKS_OBJS = $(call objs,$(LIBWASI_EMULATED_PROCESS_CLOCKS_SOURCES))
 LIBWASI_EMULATED_SIGNAL_OBJS = $(call objs,$(LIBWASI_EMULATED_SIGNAL_SOURCES))
 LIBWASI_EMULATED_SIGNAL_MUSL_OBJS = $(call objs,$(LIBWASI_EMULATED_SIGNAL_MUSL_SOURCES))
 
@@ -332,6 +335,8 @@ $(SYSROOT_LIB)/libc-printscan-no-floating-point.a: $(MUSL_PRINTSCAN_NO_FLOATING_
 
 $(SYSROOT_LIB)/libwasi-emulated-mman.a: $(LIBWASI_EMULATED_MMAN_OBJS)
 
+$(SYSROOT_LIB)/libwasi-emulated-process-clocks.a: $(LIBWASI_EMULATED_PROCESS_CLOCKS_OBJS)
+
 $(SYSROOT_LIB)/libwasi-emulated-signal.a: $(LIBWASI_EMULATED_SIGNAL_OBJS) $(LIBWASI_EMULATED_SIGNAL_MUSL_OBJS)
 
 %.a:
@@ -392,6 +397,9 @@ $(LIBC_TOP_HALF_ALL_OBJS) $(MUSL_PRINTSCAN_LONG_DOUBLE_OBJS) $(MUSL_PRINTSCAN_NO
     -Wno-dangling-else \
     -Wno-unknown-pragmas
 
+$(LIBWASI_EMULATED_PROCESS_CLOCKS_OBJS): CFLAGS += \
+    -I$(LIBC_BOTTOM_HALF_CLOUDLIBC_SRC)
+
 include_dirs:
 	$(RM) -r "$(SYSROOT)"
 
@@ -432,6 +440,7 @@ libc: include_dirs \
     $(SYSROOT_LIB)/libc-printscan-long-double.a \
     $(SYSROOT_LIB)/libc-printscan-no-floating-point.a \
     $(SYSROOT_LIB)/libwasi-emulated-mman.a \
+    $(SYSROOT_LIB)/libwasi-emulated-process-clocks.a \
     $(SYSROOT_LIB)/libwasi-emulated-signal.a
 
 finish: startup_files libc
@@ -467,7 +476,7 @@ finish: startup_files libc
 	# Generate a test file that includes all public header files.
 	#
 	cd "$(SYSROOT)" && \
-	  for header in $$(find include -type f -not -name mman.h -not -name signal.h |grep -v /bits/); do \
+	  for header in $$(find include -type f -not -name mman.h -not -name signal.h -not -name times.h -not -name resource.h |grep -v /bits/); do \
 	      echo '#include <'$$header'>' | sed 's/include\///' ; \
 	done |LC_ALL=C sort >share/$(MULTIARCH_TRIPLE)/include-all.c ; \
 	cd - >/dev/null

expected/wasm32-wasi/defined-symbols.txt

@@ -447,7 +447,6 @@ cimagl
 clearenv
 clearerr
 clearerr_unlocked
-clock
 clock_getres
 clock_gettime
 clock_nanosleep
@@ -664,7 +663,6 @@ getline
 getopt
 getopt_long
 getopt_long_only
-getrusage
 getsockopt
 getsubopt
 gettimeofday
@@ -1075,7 +1073,6 @@ tgammaf
 tgammal
 time
 timegm
-times
 timespec_get
 toascii
 tolower

expected/wasm32-wasi/include-all.c

@@ -137,7 +137,6 @@
 #include <sys/poll.h>
 #include <sys/random.h>
 #include <sys/reg.h>
-#include <sys/resource.h>
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
@@ -146,7 +145,6 @@
 #include <sys/sysinfo.h>
 #include <sys/time.h>
 #include <sys/timeb.h>
-#include <sys/times.h>
 #include <sys/timex.h>
 #include <sys/ttydefaults.h>
 #include <sys/types.h>

expected/wasm32-wasi/predefined-macros.txt

@@ -2309,14 +2309,12 @@
 #define _SYS_PARAM_H 
 #define _SYS_RANDOM_H 
 #define _SYS_REG_H 
-#define _SYS_RESOURCE_H 
 #define _SYS_SELECT_H 
 #define _SYS_SOCKET_H 
 #define _SYS_STAT_H 
 #define _SYS_SYSCALL_H 
 #define _SYS_SYSINFO_H 
 #define _SYS_TIMEB_H 
-#define _SYS_TIMES_H 
 #define _SYS_TIMEX_H 
 #define _SYS_TIME_H 
 #define _SYS_TTYDEFAULTS_H 

libc-bottom-half/clocks/clock.c

@@ -0,0 +1,32 @@
+#define _WASI_EMULATED_PROCESS_CLOCKS
+#include <time.h>
+#include <wasi/api.h>
+#include <common/time.h>
+
+_Static_assert(
+    CLOCKS_PER_SEC == NSEC_PER_SEC,
+    "This implementation assumes that `clock` is in nanoseconds"
+);
+
+// Snapshot of the monotonic clock at the start of the program.
+static __wasi_timestamp_t start;
+
+// Use a priority of 10 to run fairly early in the implementation-reserved
+// constructor priority range.
+__attribute__((constructor(10)))
+static void init(void) {
+    (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &start);
+}
+
+clock_t __clock(void) {
+    // Use `MONOTONIC` instead of `PROCESS_CPUTIME_ID` since WASI doesn't have
+    // an inherent concept of a process. Note that this means we'll incorrectly
+    // include time from other processes, so this function is only declared by
+    // the headers if `_WASI_EMULATED_PROCESS_CLOCKS` is defined.
+    __wasi_timestamp_t now = 0;
+    (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &now);
+    return now - start;
+}
+
+__attribute__((__weak__, __alias__("__clock")))
+clock_t clock(void);

libc-bottom-half/clocks/getrusage.c

@@ -0,0 +1,26 @@
+#define _WASI_EMULATED_PROCESS_CLOCKS
+#include <sys/resource.h>
+#include <errno.h>
+#include <time.h>
+#include <wasi/api.h>
+#include <common/time.h>
+
+clock_t __clock(void);
+
+int getrusage(int who, struct rusage *r_usage) {
+    switch (who) {
+    case RUSAGE_SELF: {
+        __wasi_timestamp_t usertime = __clock();
+        *r_usage = (struct rusage) {
+            .ru_utime = timestamp_to_timeval(usertime)
+	};
+        return 0;
+    }
+    case RUSAGE_CHILDREN:
+        *r_usage = (struct rusage) {};
+        return 0;
+    default:
+        errno = EINVAL;
+        return -1;
+    }
+}

libc-bottom-half/clocks/times.c

@@ -0,0 +1,24 @@
+#define _WASI_EMULATED_PROCESS_CLOCKS
+#include <time.h>
+#include <sys/times.h>
+#include <wasi/api.h>
+#include <common/time.h>
+
+_Static_assert(
+    CLOCKS_PER_SEC == NSEC_PER_SEC,
+    "This implementation assumes that `clock` is in nanoseconds"
+);
+
+clock_t __clock(void);
+
+clock_t times(struct tms *buffer) {
+    __wasi_timestamp_t user = __clock();
+    *buffer = (struct tms){
+        .tms_utime = user,
+        .tms_cutime = user
+    };
+
+    __wasi_timestamp_t realtime = 0;
+    (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &realtime);
+    return realtime;
+}

libc-top-half/musl/include/sys/param.h

@@ -28,7 +28,9 @@
 #define roundup(n,d) (howmany(n,d)*(d))
 #define powerof2(n) !(((n)-1) & (n))
 
+#if defined(__wasilibc_unmodified_upstream) || defined(_WASI_EMULATED_PROCESS_CLOCKS)
 #include <sys/resource.h>
+#endif
 #include <endian.h>
 #include <limits.h>
 

libc-top-half/musl/include/sys/resource.h

@@ -1,3 +1,8 @@
+#ifndef _WASI_EMULATED_PROCESS_CLOCKS
+#error WASI lacks process-associated clocks; to enable emulation of the `getrusage` function using \
+the wall clock, which isn't sensitive to whether the program is running or suspended, \
+compile with -D_WASI_EMULATED_PROCESS_CLOCKS and link with -lwasi-emulated-process-clocks
+#else
 #ifndef	_SYS_RESOURCE_H
 #define	_SYS_RESOURCE_H
 
@@ -118,3 +123,4 @@ __REDIR(getrusage, __getrusage_time64);
 #endif
 
 #endif
+#endif

libc-top-half/musl/include/sys/times.h

@@ -1,3 +1,8 @@
+#ifndef _WASI_EMULATED_PROCESS_CLOCKS
+#error WASI lacks process-associated clocks; to enable emulation of the `times` function using \
+the wall clock, which isn't sensitive to whether the program is running or suspended, \
+compile with -D_WASI_EMULATED_PROCESS_CLOCKS and link with -lwasi-emulated-process-clocks
+#else
 #ifndef	_SYS_TIMES_H
 #define	_SYS_TIMES_H
 
@@ -26,4 +31,4 @@ clock_t times (struct tms *);
 #endif
 
 #endif
-
+#endif

libc-top-half/musl/include/time.h

@@ -58,7 +58,16 @@ struct tm {
 #include <__header_time.h>
 #endif
 
+#if defined(__wasilibc_unmodified_upstream) || defined(_WASI_EMULATED_PROCESS_CLOCKS)
 clock_t clock (void);
+#else
+__attribute__((__deprecated__(
+"WASI lacks process-associated clocks; to enable emulation of the `clock` function using "
+"the wall clock, which isn't sensitive to whether the program is running or suspended, "
+"compile with -D_WASI_EMULATED_PROCESS_CLOCKS and link with -lwasi-emulated-process-clocks"
+)))
+clock_t clock (void);
+#endif
 time_t time (time_t *);
 double difftime (time_t, time_t);
 time_t mktime (struct tm *);

libc-top-half/musl/src/conf/sysconf.c

@@ -1,7 +1,9 @@
 #include <unistd.h>
 #include <limits.h>
 #include <errno.h>
+#ifdef __wasilibc_unmodified_upstream // WASI has no process-level accounting
 #include <sys/resource.h>
+#endif
 #ifdef __wasilibc_unmodified_upstream // WASI has no realtime signals
 #include <signal.h>
 #endif