Hi,
We use an RTC and the POSIX function mktime() to convert a broken-down time into a time in seconds.
Function prototype: time_t mktime(struct tm *tm);
Problem is: this mktime() function has the 2038 year bug (see here https://en.wikipedia.org/wiki/Year_2038_problem for details).
Here is a small test function:
#include <stdio.h>
#include <time.h>
struct timeval testTimeval(void)
{
struct timeval time;
struct tm t_decomp;
time.tv_sec = -1;
t_decomp.tm_year = 139; //2039
t_decomp.tm_mon = 0;
t_decomp.tm_mday = 1;
t_decomp.tm_hour = 8;
t_decomp.tm_min = 37;
t_decomp.tm_sec = 53;
t_decomp.tm_isdst = -1;
time.tv_sec = mktime(&t_decomp);
time.tv_usec = 0;
printf("t_decomp : %d-%d-%d => %llds, sizeof(time.tv_sec) = %d\r\n", t_decomp.tm_year, t_decomp.tm_mon, t_decomp.tm_mday, (long long int)time.tv_sec, sizeof(time.tv_sec));
}
//This fonction prints:
//t_decomp : 139-0-1 => -2117483423s, sizeof(time.tv_sec) = 8
//note that the time returned by mktime() is negative, which should not be the case for the year 2039. Also note that sizeof(time_t) is 8, so the time is stored in a 64 bits variable (not 32 bits), which is fine.
//Which is decoded into 1902-11-26 02:09:37,000 (instead of 2039-01-01)
//If I set the year to 2038, everything is OK:
//t_decomp : 138-0-1 => 2145948149s, sizeof(time.tv_sec) = 8
//Note that the time returned is positive this time
//And decoding the time back gives 2038-01-01 08:42:29,000 which is fine
Sum-up: any year above 2038 passed to mktime() function will result in wrong returned value and a year rolling back to 19xx.
Note: the bug is not due to the "time_t" type which is a 64 bit variable for the STM32 (fine for the year 2038), but most likely to a bug into the mktime() function itself which I guess uses 32 bits signed internal types internally. Where can I find the source code of the STM32 toolchain to check my assumptions?
Anyway, I have used an external mktime() function from here, and everything is working fine, so I am quite confident that the bug is inside the STM32 toolchain.
I am using STM32L4A6 with System Workbench (SW4STM32) and gcc version 7.2.1 20170904 (release) [ARM/embedded-7-branch revision 255204] (GNU Tools for Arm Embedded Processors 7-2017-q4-major)
