[uClibc] Which one to use

[Eric]

I am now writing a bootloader on arm7tdmi. When I link the files, I got an
undefined reference to '_bootstrap' at si.S. I have everything inside the
same directory. I got 5 files.

<head.c>
extern void main(void);
void bootstrap(void) {
    typedef void(*ENTRY)(void);
    ENTRY entry_addr;
    entry_addr = &main;
    (*entry_addr)();
}

<ld.script>
ENTRY(main)
SECTIONS
{
    .reset : {
        si.o
    }
    .text : {*(.text)}
    .bss : {*(.bss)}
    .data : {*(.data)}
}

<sim.c>
int main(int argc, char *argv[])
{
    unsigned int abc;
    abc=0;
    return(0);
}

<si.S>
    .text
    .align
    .global    _start
_start:
    mov r0,#0xD3
    msr cpsr, r0
    b _bootstrap

Did I make anything wrong?
More, I have find two sets of toolchain. One is arm-elf-gcc and the other is
arm-linux-gcc. Which one should I use when I want to compile a bootloader?

Thanks,

Eric