How to debug

[Jezze]

Ok, this is kinda embarrasing but I just don't know.

I'm trying to run programs compiled by my own toolchain including newlib and ran into a weird issue.

This is my test program:

Code: Select all

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[])
{

    write(STDOUT_FILENO, "test1\n", 6);

//    FILE *out = fopen("stdout", "w");

    fputs("test2\n", stdout);

//    FILE *out = fopen("stdout", "w");

    return 0;

}

If I do not uncomment any of the comments my program will work and print test1 and test2 but if I either uncomment the first or the second (obviously not both) it will only print test1 before page fault giving me a very low memory address, either 0x17e4 or 0x88. Especially notice that uncommenting the second line would still only print test1.

Any hints on what could be wrong? I know I'm not zeroing bss on program loading, which could be a start but I don't see why that would matter in this case.

[bluemoon]

I know I'm not zeroing bss on program loading, which could be a start but I don't see why that would matter in this case.

It's because newlib require you to zero bss. By not doing so you probably left some internal data structure to be random.

[Jezze]

Ok I think I zeroed the bss now, but the problem still exist.

I added this code which probably should be enough:

Code: Select all

void elf_zero_bss(void *address)
{

    struct elf_header *header = get_header(address);

    if (!header)
        return;

    struct elf_section_header *sheader = address + header->shoffset;

    unsigned int i;

    for (i = 0; i < header->shnum; i++)
    {

        if (sheader[i].type == 8)
            memory_clear(address + sheader[i].offset, sheader[i].size);

    }

}