toolchain/musl/patches/110-read_timezone_from_fs.patch

--- a/src/time/__tz.c
+++ b/src/time/__tz.c
@@ -5,6 +5,10 @@
 #include <string.h>
 #include <sys/mman.h>
 #include <ctype.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include "libc.h"
 #include "lock.h"
 #include "fork_impl.h"
@@ -123,6 +127,67 @@ static size_t zi_dotprod(const unsigned
 	return y;
 }
 
+#define TZ_BUFLEN		(2*TZNAME_MAX + 56)
+static char *read_TZ_file(char *buf)
+{
+	int r;
+	int fd;
+	char *p = NULL;
+
+	fd = open("/etc/TZ", O_RDONLY);
+	if (fd >= 0) {
+		/* Shorter, and does one fewer read syscall */
+		r = read(fd, buf, TZ_BUFLEN);
+		if (r < 0)
+			goto ERROR;
+		p = buf + r;
+
+		if ((p > buf) && (p[-1] == '\n')) { /* Must end with newline */
+			p[-1] = 0;
+			p = buf;
+		} else {
+ERROR:
+			p = NULL;
+		}
+		close(fd);
+	} else {
+		fd = open("/etc/localtime", O_RDONLY);
+		if (fd >= 0) {
+			r = read(fd, buf, TZ_BUFLEN);
+			if (r != TZ_BUFLEN
+			 || strncmp(buf, "TZif", 4) != 0
+			 || (unsigned char)buf[4] < 2
+			 || lseek(fd, -TZ_BUFLEN, SEEK_END) < 0
+			) {
+				goto ERROR;
+			}
+			/* tzfile.h from tzcode database says about TZif2+ files:
+			**
+			** If tzh_version is '2' or greater, the above is followed by a second instance
+			** of tzhead and a second instance of the data in which each coded transition
+			** time uses 8 rather than 4 chars,
+			** then a POSIX-TZ-environment-variable-style string for use in handling
+			** instants after the last transition time stored in the file
+			** (with nothing between the newlines if there is no POSIX representation for
+			** such instants).
+			*/
+			r = read(fd, buf, TZ_BUFLEN);
+			if (r <= 0 || buf[--r] != '\n')
+				goto ERROR;
+			buf[r] = 0;
+			while (r != 0) {
+				if (buf[--r] == '\n') {
+					p = buf + r + 1;
+					break;
+				}
+			} /* else ('\n' not found): p remains NULL */
+			close(fd);
+		}
+	}
+
+	return p;
+}
+
 static void do_tzset()
 {
 	char buf[NAME_MAX+25], *pathname=buf+24;
@@ -131,8 +196,15 @@ static void do_tzset()
 	size_t i;
 	static const char search[] =
 		"/usr/share/zoneinfo/\0/share/zoneinfo/\0/etc/zoneinfo/\0";
+	char tzbuf[TZ_BUFLEN];
 
 	s = getenv("TZ");
+
+	/* if TZ is empty try to read it from /etc/TZ */
+	if (!s || !*s) {
+		s = read_TZ_file(tzbuf);
+	}
+
 	if (!s) s = "/etc/localtime";
 	if (!*s) s = __utc;