[GCC_CR] non-RTOS build code doesn't reach to the main() function

[toyowata]

An exported project to LPCXpresso IDE (GCC_CR build) doesn't reach to the main() function for baremetal (non-RTOS) build.
Automate test result of the LPC1768 is below:

Test summary:
+---------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
| Result  | Target  | Toolchain | Test ID     | Test Description                      | Elapsed Time (sec) | Timeout (sec) | Loops |
+---------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
| TIMEOUT | LPC1768 | GCC_CR    | DTCT_1      | Simple detect test                    |       20.07        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | EXAMPLE_1   | /dev/null                             |       20.07        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_10     | Hello World                           |       20.07        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_11     | Ticker Int                            |       40.33        |       20      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_12     | C++                                   |       20.08        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_16     | RTC                                   |       30.25        |       15      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_2      | stdio                                 |       40.34        |       20      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_22     | Semihost                              |       20.14        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_23     | Ticker Int us                         |       30.25        |       15      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_24     | Timeout Int us                        |       30.25        |       15      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_25     | Time us                               |       30.23        |       15      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_26     | Integer constant division             |       20.08        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_34     | Ticker Two callbacks                  |       30.22        |       15      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_37     | Serial NC RX                          |        20.1        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_38     | Serial NC TX                          |       20.12        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_A1     | Basic                                 |       20.07        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_A18    | Interrupt vector relocation           |       20.09        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_A2     | Semihost file system                  |       20.12        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_A21    | Call function before main (mbed_main) |       20.13        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_A9     | Serial Echo at 115200                 |       20.09        |       10      |  0/1  |
| TIMEOUT | LPC1768 | GCC_CR    | MBED_BUSOUT | BusOut                                |       30.21        |       15      |  0/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_1      | Basic thread                          |       12.69        |       15      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_2      | Mutex resource lock                   |       12.84        |       20      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_3      | Semaphore resource lock               |        9.81        |       20      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_4      | Signals messaging                     |        7.78        |       20      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_5      | Queue messaging                       |        3.7         |       20      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_6      | Mail messaging                        |        3.71        |       20      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_7      | Timer                                 |       12.62        |       15      |  1/1  |
| OK      | LPC1768 | GCC_CR    | RTOS_8      | ISR (Queue)                           |        7.81        |       20      |  1/1  |
+---------+---------+-----------+-------------+---------------------------------------+--------------------+---------------+-------+
Result: 8 OK / 21 TIMEOUT

Completed in 732.83 sec

This was because the software_init_hook() function was defined here with strong (non-weak) symbol by this change.

43e595a

Original code in the reset vector startup code for GCC_CR is below:

extern "C" void software_init_hook(void) __attribute__((weak));

AFTER_VECTORS void ResetISR(void) {

// snip

    SystemInit();
    if (software_init_hook) // give control to the RTOS
        software_init_hook(); // this will also call __libc_init_array
    else {
        __libc_init_array();
        main();
    }
    while (1) {;}
}

The software_init_hook symbol is now defined as strong rather than weak, therefore if (software_init_hook) statement is always true even an mbed-rtos library is not linked. i.e. baremetal project.

I tried to use a software_init_hook_rtos symbol instead which is weakly defined in retarget.cpp, but this was strongly linked into the ResetISR startup code because they were in the same static library. See: http://stackoverflow.com/questions/23079997/override-weak-symbols-in-static-library

When I use pre_main symbol which is weakly defined in other static library (mbed-rtos) and it works as expected. I will make PR once my local test has been completed.

[toyowata]

#2582 merged