musl - Possible issue formatting epoch time with strftime()

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Message-ID: <70c350e5-78cd-4ab9-ae9b-598179ee4f8e@pgbackrest.org>
Date: Mon, 02 Jun 2025 19:33:41 +0000 (UTC)
From: David Steele <david@...ackrest.org>
To: musl@...ts.openwall.com
Subject: Possible issue formatting epoch time with strftime()

Greetings,

I've been working on getting the pgBackRest unit tests working with musl 
libc. While there are some small differences from glibc that I have been 
able to work out I have found one issue that I can't solve or work around.

Given the test program:

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main()
{
     time_t time = 1573222014;
     char buffer[128];

     setenv("TZ", "America/New_York", true);
     tzset();

     strftime(buffer, sizeof(buffer), "%s", localtime(&time));
     printf("local epoch: %s\n", buffer);

     strftime(buffer, sizeof(buffer), "%s", gmtime(&time));
     printf("utc epoch: %s\n", buffer);

     strftime(buffer, sizeof(buffer), "%Y%m%d-%H%M%S", localtime(&time));
     printf("local time: %s\n", buffer);

     strftime(buffer, sizeof(buffer), "%Y%m%d-%H%M%S", gmtime(&time));
     printf("utc time: %s\n", buffer);
}

I get different output for musl vs gnu vs mac:

Ubuntu 22.04 (UTC) gcc:

local epoch: 1573222014
utc epoch: 1573240014
local time: 20191108-090654
utc time: 20191108-140654

Mac OS 15.4.1 (America/New_York) clang:

local epoch: 1573222014
utc epoch: 1573240014
local time: 20191108-090654
utc time: 20191108-140654

Alpine 3.21 (America/New_York or UTC) gcc/musl:

local epoch: 1573222014
utc epoch: 1573222014        <------
local time: 20191108-090654
utc time: 20191108-140654

I tried Alpine with system timezone set to America/New_York and UTC and 
got the same epoch result with both but formatting the time with 
%Y%m%d-%H%M%S give the expected result.

Am I missing something?

Please CC me as I am not subscribed to the list.

Regards,
-David

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