string literals break kernel

[Sages]

Hi everyone, I apologize for the total newb question I'm about to ask but for someone reason my kernel doesn't print text correctly when I use a string literal. Here is a sample.

Code: Select all

void KernelEntry()
{
    ...
    // This version works fine
    char strMe[3] = { 'M', 'e', 0 };

    // but if I use this instead...
    char strMe[] = "Me";    // this causes nothing to print    
    PrintString(strMe);
    ...
}

I'm new to all of this and would like to thank you all in advance for any help you may be able to give me. Oh, and I am using a linker script which places my text segment above .data and .bss. my tools are gcc, nasm and ld.

[Candy]

default guess: the string is recognised as read-only and thus put with the code.

Solutions: configure the rodata to end up properly, fix your pointers, use -fwritable-strings or put .rodata in .data in your linker script.

[Sages]

I am using the -fwritable-strings option but I'm not too sure what that .rodata stuff is about. could you please expand on that? This is my current linker script.

Code: Select all

OUTPUT_FORMAT("binary")
ENTRY(_start)
SECTIONS
{
  .text 0x10000 : {
    *(.text)
  }
  .data : {
    *(.data)
  }
  .bss : {
    *(.bss)
  }
}

[Sages]

well, the problem was... I'm retarded. Unfortunately that's do to a genetic defect that I can't change. However, I did manage to get the code to work.

kernel.lnk...

Code: Select all

...
  .text 0x10000    #  << I'm only off by a power of 2
  .text 0x100000   # << amazing what a missing zero can do
...

but if anyone could please explain what that .rodata segment was I'd appreciate it. Or I suppose I could just google for it. Well thanks for you help.

[Candy]

.rodata == read only data

what your strings are put in if you don't put them in .data (with -fwritable-strings). That part is data but can be put in the .text section to save overhead with program texts being multiply mapped.

[Dragon88]

I have this problem too. I'm not using a linker script though, what can I do? If I use -fwritable-strings it puts the strings directly in front of the code and it doesn't work right.

[Tim]

Use a linker script and put the .rodata section in with the .text section. Then you don't have to use -fwriteable-strings.

[bubach]

char strMe[] = "Me"; // this causes nothing to print

where is the zero in that? u need to have a zero in the end just like u had in :

char strMe[3] = { 'M', 'e', 0 };

/ Christoffer

[Tim]

The zero is added automatically by the compiler. All "quoted strings" are nul-terminated; otherwise no quoted strings would work.

[bubach]

Ok, stupid me..