mktime() uses UTC instead of local timezone

[endrift]

mktime() is supposed to use the local timezone, whereas the UTC equivalent is supposed to be gmtime(). However, since there is no TZ environment variable set up in the environment, mktime() winds up using UTC instead of the local time zone. This is the root cause of mgba-emu/mgba#2876, which I worked around in mgba-emu/mgba@e8ef801. A similar implementation may be plausible in newlib.

[isage]

Possible implementation (marked with comments) that should go into newlib startup

#define _POSIX_C_SOURCE 200112L // for setenv on gcc
#include <stdlib.h>
#include <stdio.h>
#include <time.h>

#include <psp2/apputil.h>
#include <psp2/system_param.h>
 
int main(void)
{
    struct tm time_str;

    time_str.tm_year = 2023;
    time_str.tm_mon = 4;
    time_str.tm_mday = 4;
    time_str.tm_hour = 12;
    time_str.tm_min = 0;
    time_str.tm_sec = 0;
    time_str.tm_isdst = -1;

    time_t t = mktime(&time_str);
    sceClibPrintf("%s", asctime(&time_str));
    sceClibPrintf("t = %d\n", t);

// -- set tz
    SceAppUtilInitParam initParam;
    SceAppUtilBootParam bootParam;
    memset(&initParam, 0,  sizeof(SceAppUtilInitParam));
    memset(&bootParam, 0,  sizeof(SceAppUtilBootParam));
    int ret = sceAppUtilInit( &initParam, &bootParam );

    SceInt32 offset;
    ret = sceAppUtilSystemParamGetInt(SCE_SYSTEM_PARAM_ID_TIME_ZONE, &offset);
    sceClibPrintf("ret = 0x%08x, offset %d\n", ret, offset);
    char tz[10];
    if (offset < 0)
    {
        offset *=-1;
        sprintf(tz, "UTC-%d:%d", offset / 60, offset % 60);
        sceClibPrintf("TZ= %s\n", tz);
    }
    else
    {
        sprintf(tz, "UTC+%d:%d", offset / 60, offset % 60);
        sceClibPrintf("TZ= %s\n", tz);
    }

    setenv("TZ",tz,1);

// -- end set tz


    t = mktime(&time_str);
    sceClibPrintf("%s", asctime(&time_str));
    sceClibPrintf("t = %d\n", t);

}

Feel free to adapt and pr.

[endrift]

Using sceAppUtilInit in the startup seems risky for existing homebrew, especially since the init and boot parameters just get thrown out.

[isage]

Nothing risky, if you call sceAppUtilShutdown afterwards