libc/minimal: static variable of gmtime() does not located to z_libc_partition at usermode.

[atsushi-shinbo-esoltrinity]

Describe the bug
A access fault occur when call gmtime() from a user thread.

gmtime() have a static allocated variable named "struct tm shared".
(zephyr/lib/libc/minimal/source/time/gmtime.c)
This variable is defined locally in the function, but allocated statically. So, it should be located to z_libc_partition.
Currently it is not. Therefore, an access fault occur when call gmtime() from user thread.

Issue 1:
The variable "shared" in gmtime() should be qualified with LIBC_DATA same as minimal/source/stdlib/rand.c.

static LIBC_DATA struct tm shared;

Issue 2:
Currently, to create "z_libc_partition" parition, CONFIG_MINIMAL_LIBC_RAND is also needed.
This configuration should only relate to rand function, not time function.

To Reproduce

1. Modify samples/userspace/hello_world_user/src/main.c as following.

#include <zephyr.h>
#include <stdio.h>
#include <time.h>				// time_t
#include <sys/libc-hooks.h>		// z_libc_partition

#define USER_STACKSIZE	1024

struct k_thread user_thread;
K_THREAD_STACK_DEFINE(user_stack, USER_STACKSIZE);

static struct k_mem_domain user_domain;

static struct k_mem_partition *user_parts[] = {
	&z_libc_partition,
};

static void user_function(void *p1, void *p2, void *p3)
{
	printf("Hello World from UserSpace! %s\n", CONFIG_BOARD);
	
	time_t sec_time = 1234567890;	// 2009/02/13 23:31:30
	struct tm* tm_time = gmtime(&sec_time);
	printf("%02d/%02d/%02d %02d:%02d:%02d\n", 
		tm_time->tm_year + 1900,
		tm_time->tm_mon + 1,
		tm_time->tm_mday,
		tm_time->tm_hour,
		tm_time->tm_min,
		tm_time->tm_sec);
}

static void entry_user_function() {
	
	k_mem_domain_init(&user_domain, ARRAY_SIZE(user_parts), user_parts);
	k_mem_domain_add_thread(&user_domain, k_current_get());
	
	k_thread_user_mode_enter(user_function, NULL, NULL, NULL);
}

void main(void)
{
	k_thread_create(&user_thread, user_stack, USER_STACKSIZE,
			entry_user_function, NULL, NULL, NULL,
			-1, K_INHERIT_PERMS, K_MSEC(0));
}

2. Add following lines to samples/userspace/hello_world_user/prj.conf

CONFIG_MINIMAL_LIBC=y
CONFIG_MINIMAL_LIBC_RAND=y

3. west build -b hifive1_revb samples/userspace/hello_world_user
4. cd build/zephyr
5. $ZEPHYR_SDK_INSTALL_DIR/riscv64-zephyr-elf/bin/riscv64-zephyr-elf-objcopy -O ihex zephyr.elf zephyr.hex
6. Write zephyr.hex to the Hifive1 revB board and run.

Expected behavior
gmtime() can be called from user thread when the thread have a permission to access "z_libc_partition".

Impact
I can use gmtime_r() instead of gmtime().
However, some library may use gmtime(), especially mbedtls. A example call flow is here.

mbedtls_x509_crt_verify()
 -> mbedtls_x509_time_is_past()
  -> x509_get_current_time()
   -> mbedtls_platform_gmtime_r()
    -> gmtime()

Logs and console output

*** Booting Zephyr OS version 2.7.99  ***
Hello World from UserSpace! hifive1_revb
E:
E:  mcause: 7, Store/AMO access fault
E:   mtval: 8000038c
E:      a0: 8000038c    t0: 20014004
E:      a1: 00000000    t1: 00000000
E:      a2: 800003b0    t2: 7fffffff
E:      a3: 00000000    t3: 499602d2
E:      a4: 000037d0    t4: a5690000
E:      a5: 8000038d    t5: 00000000
E:      a6: 00000000    t6: 00000000
E:      a7: a8c00000
E:                      tp: 2001f568
E:      ra: 20014548
E:    mepc: 2001425c
E: mstatus: 00000080
E:
E: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
E: Current thread: 0x80000050 (unknown)
E: Halting system

Expected output (after workaround)

*** Booting Zephyr OS version 2.7.99  ***
Hello World from UserSpace! hifive1_revb
2009/02/13 23:31:30

Environment (please complete the following information):

• OS: Ubuntu 18.04.5 LTS
• Toolchain: zephyr-sdk-0.13.1
• Version: v2.7.99
• Commit: 1238410
• Target: hifive1_revb
• modules/crypto/mbedtls : "mbed TLS 3.0.0" (bf66e18046a96e83b6ef3bb4bec0ae81bdcefc68)

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[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.