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cgcclinkerld

Where are the symbols etext, edata and end defined?

This is a code from Linux man page:

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

extern char etext, edata, end;

int main() {
    printf("First address past:\n");
    printf("    program text (etext)      %10p\n", &etext);
    printf("    initialized data (edata)  %10p\n", &edata);
    printf("    uninitialized data (end)  %10p\n", &end);

    exit(EXIT_SUCCESS);
}

when run, the program below produces output such as the following:

$ ./a.out
First address past:
    program text (etext)       0x8048568
    initialized data (edata)   0x804a01c
    uninitialized data (end)   0x804a024

Where are etext, edata end defined ? How those symbols are assigned values ? Is it by linker or something else ?

Solution

  • These symbols are defined in a linker script file (dead link copy at archive.org).