all: properly handle time_t on 32-bit platforms

Do not force 64-bit `time_t` on 32-bit platforms, since libfuse
does not do so.  Linking shared objects with incompatible types
breaks ABI, resulting in undefined behavior.

Instead, add run-time checks to make sure that timestamps do not
overflow.  If they do, set to `INT32_MAX`.

Also tidy up build scripts, tests, and the installation guide.

INSTALL.md

@@ -166,19 +166,6 @@ Notes
   In this case, the utility library will not be built from source,
   and other components will link to the specified library instead.
 
- ### Targeting 32-bit Platforms
-
-  BookmarkFS requires 64-bit `off_t` and `time_t`, which may not be supported
-  on 32-bit platforms (e.g., i386 FreeBSD does not support 64-bit `time_t`).
-
-  If using Autoconf 2.72 or later, the configuration script automatically
-  performs checks and defines necessary macros, and fails if unsupported.
-  With legacy Autoconf, only `off_t` is checked.
-
-  To manually configure 64-bit `time_t`, add preprocessor flags
-  `-D_TIME_BITS=64` (or something equivalent, depending on the toolchain).
-  If unsupported, `make` will fail.
-
  ### FreeBSD and GNU libiconv
 
   NOTE: You may skip this section if _not_ building the Chromium backend.

configure.ac

@@ -196,18 +196,7 @@ AS_VAR_IF([ac_have_largefile], [no], [
     ]))
 ])
 
-m4_version_prereq([2.72], [
+AX_COMPILE_CHECK_SIZEOF([time_t])
-    AC_SYS_YEAR2038
-    AS_VAR_IF([ac_have_year2038], [no], [
-        AC_MSG_ERROR(m4_normalize([
-            64-bit time_t is unsupported on this platform.
-        ]))
-    ])
-], [
-    dnl  fallback to compile-time check...
-    AX_COMPILE_CHECK_SIZEOF([time_t])
-])
-
 AX_COMPILE_CHECK_SIZEOF([uintptr_t], [#include <stdint.h>])
 
 # -- Output --

src/backend_chromium.c

@@ -58,17 +58,14 @@
 #include "watcher.h"
 #include "xstd.h"
 
-#if defined(SIZEOF_TIME_T) && (SIZEOF_TIME_T != 8)
-#  error "64-bit time_t is required"
-#endif
-
 #define BACKEND_FILENAME_GUID  ( 1u << 16 )
 
-// Chromium uses Windows FILETIME epoch instead of Unix epoch.
+// Chromium uses Windows FILETIME epoch, which is
+// `((1970 - 1601) * 365 + 89) * 24 * 3600` seconds before the Unix epoch.
 //
 // See Chromium source code: /base/time/time.h
 // (`base::Time::kTimeTToMicrosecondsOffset`)
-#define EPOCH_DIFF  ( (time_t)((1970 - 1601) * 365 + 89) * 24 * 3600 )
+#define EPOCH_DIFF  INT64_C(11644473600)
 
 #define BOOKMARKS_ROOT_ID  0
 
@@ -387,7 +384,7 @@ build_tsnode (
         ts = &now;
     }
 
-    time_t  secs      = ts->tv_sec + EPOCH_DIFF;
+    int64_t secs      = ts->tv_sec + EPOCH_DIFF;
     int64_t microsecs = secs * 1000000 + ts->tv_nsec / 1000;
 
     char buf[32];
@@ -1461,12 +1458,17 @@ parse_ts (
     }
 
     if (buf != NULL) {
-        time_t secs = microsecs / 1000000;
+        int64_t secs = microsecs / 1000000 - EPOCH_DIFF;
-        if (unlikely(secs < EPOCH_DIFF)) {
+        if (unlikely(secs < 0)) {
             // Stay away from negative tv_sec
-            secs = EPOCH_DIFF;
+            secs = 0;
         }
-        buf->tv_sec  = secs - EPOCH_DIFF;
+#if defined(SIZEOF_TIME_T) && (SIZEOF_TIME_T < 8)
+        else if (secs > INT32_MAX) {
+            secs = INT32_MAX;
+        }
+#endif
+        buf->tv_sec  = secs;
         buf->tv_nsec = (microsecs % 1000000) * 1000;
     }
     return 0;

src/backend_firefox.c

@@ -2135,7 +2135,7 @@ static int64_t
 timespec_to_usecs (
     struct timespec const *ts
 ) {
-    return ts->tv_sec * 1000000 + ts->tv_nsec / 1000;
+    return (int64_t)ts->tv_sec * 1000000 + ts->tv_nsec / 1000;
 }
 
 static int
@@ -2778,11 +2778,16 @@ usecs_to_timespec (
     struct timespec *ts_buf,
     int64_t          microsecs
 ) {
-    if (unlikely(microsecs < 0)) {
+    int64_t secs = microsecs / 1000000;
-        microsecs = 0;
+    if (unlikely(secs < 0)) {
+        secs = 0;
     }
-
+#if defined(SIZEOF_TIME_T) && (SIZEOF_TIME_T < 8)
-    ts_buf->tv_sec  = microsecs / 1000000;
+    else if (secs > INT32_MAX) {
+        secs = INT32_MAX;
+    }
+#endif
+    ts_buf->tv_sec  = secs;
     ts_buf->tv_nsec = (microsecs % 1000000) * 1000;
 }
 

tests/check_fs_times.c

@@ -31,13 +31,14 @@
 #include <unistd.h>
 
 #include "check_util.h"
+#include "backend_util.h"
 #include "frontend_util.h"
 #include "prng.h"
 
 // Forward declaration start
 static int  compare_timespec  (struct timespec, struct timespec);
 static int  do_check_fs_times (int, int);
-static void usecs_to_timespec (struct timespec *, uint32_t);
+static void usecs_to_timespec (struct timespec *, uint64_t);
 // Forward declaration end
 
 static int
@@ -113,9 +114,8 @@ do_check_fs_times (
     ASSERT_NE(-1, compare_timespec(stat_buf.st_atim, now));
 
     for (int i = 0; i < rounds; ++i) {
-        uint64_t bits = prng_rand();
+        usecs_to_timespec(&times[0], prng_rand());
-        usecs_to_timespec(&times[0], bits & 0xffffffff);
+        usecs_to_timespec(&times[1], prng_rand());
-        usecs_to_timespec(&times[1], bits >> 32);
 
         ASSERT_EQ(0, futimens(fd, times));
         ASSERT_EQ(0, fstat(fd, &stat_buf));
@@ -142,9 +142,15 @@ do_check_fs_times (
 static void
 usecs_to_timespec (
     struct timespec *ts_buf,
-    uint32_t         usecs
+    uint64_t         usecs
 ) {
-    ts_buf->tv_sec  = usecs / 1000000;
+    int64_t secs = usecs / 1000000;
+#if defined(SIZEOF_TIME_T) && (SIZEOF_TIME_T < 8)
+    secs %= (int64_t)INT32_MAX + 1;
+#else
+    secs %= TIMESPEC_SEC_MAX + 1;
+#endif
+    ts_buf->tv_sec  = secs;
     ts_buf->tv_nsec = (usecs % 1000000) * 1000;
 }