1#define _WASI_EMULATED_PROCESS_CLOCKS
2#include <time.h>
3#include <wasi/api.h>
4#include <common/time.h>
5
6_Static_assert(
7 CLOCKS_PER_SEC == NSEC_PER_SEC,
8 "This implementation assumes that `clock` is in nanoseconds"
9);
10
11// Snapshot of the monotonic clock at the start of the program.
12static __wasi_timestamp_t start;
13
14// Use a priority of 10 to run fairly early in the implementation-reserved
15// constructor priority range.
16__attribute__((constructor(10)))
17static void init(void) {
18 (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &start);
19}
20
21// Define the libc symbol as `__clock` so that we can reliably call it
22// from elsewhere in libc.
23clock_t __clock(void) {
24 // Use `MONOTONIC` instead of `PROCESS_CPUTIME_ID` since WASI doesn't have
25 // an inherent concept of a process. Note that this means we'll incorrectly
26 // include time from other processes, so this function is only declared by
27 // the headers if `_WASI_EMULATED_PROCESS_CLOCKS` is defined.
28 __wasi_timestamp_t now = 0;
29 (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &now);
30 return now - start;
31}
32
33// Define a user-visible alias as a weak symbol.
34__attribute__((__weak__, __alias__("__clock")))
35clock_t clock(void);