Re: [ECOS] Question eCOS debugging. Thanks a lot.

[Jonathan Larmour <jifl at eCosCentric dot com>]

QiangHuang wrote:
> Hi all:
>      I am trying to get a clear calling path of RedBoot with the hal stub
> and GDB debugger. I can't understand the following, could anybody please
> give me some idea? Thanks a lot.
>
> In HAL/ARM function "hal_syscall_handler()" getting the saved ARM register
> by calling:

hal_syscall_handler is called when a trap is made. This is intended to be 
used by newlib based apps.

> Step 1. func = get_register(R0);   arg1 = get_register(R1);    arg2 =
> get_register(R2);    arg3 = get_register(R3);
> Step 2. and later call into RedBoot by function "__do_syscall(func, arg1,
> arg2, arg3, arg4, &err, &sig)",
> Step 3. in turns call into gdb_fileio function: "cyg_hal_gdbfileio_xxx()",
> take write for example: cyg_hal_gdbfileio_write((int)arg1, (const void
> *)arg2, (size_t)arg3, (int *)sig);
> Here arg2 will be treated as a buffer pointer, but Isn't "arg2" = "saved ARM
> register R2"? so where is this pointer pointing to?

Yes, R2 when the syscall was invoked. See newlib's 
libgloss/arm/redboot-syscalls.c, e.g.
int
_write(int fd, const char *buf, int nbytes)
{
    int err;

    err = __syscall(SYS_write, fd, buf, nbytes);
    if (err<0)
      {
        errno = -err;
        return -1;
      }
    return err;
}


> I would like to know how the processor registers are retrieved (by the HAL
> Stub and RedBoot) and display on the GDB debugger(Insight)? Thanks a lot.

Loosely, processor context is saved in vectors.S. Exception handler VSR 
chains to hal_misc.c's "exception_handler()" which calls into the GDB stub 
with _handle_exception after setting the global _hal_registers to the 
saved state. Later on the GDB stub then uses HAL_GET_GDB_REGISTERS from 
the arch HAL's include/hal_arch.h to convert the saved register state into 
the state GDB needs.

Jifl
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