To the best of my understanding, static variables that are not explicitely initialized (and, with GCC, even those that are explicitely initialized to zero if -fzero-initialized-in-bss is set, which is the case by default) are usually stored in the BSS segment. Yet, it seems that when I try to inspect that behaviour, those variables are stored in the general data section (with initialized globals). If I compile (with -O0 for good measure) and run:
#include <stdio.h> #include <stdlib.h> extern char etext, edata, end; int i = 42; int main(int argc, char* argv[]) { static int j; printf ("end of program (etext) = %10p\n",&etext); printf ("end of initialized data (edata) = %10p\n",&end); printf ("end of uninitialized data (end) = %10p\n",&end); printf ("=====\n"); printf ("Value of i (initialized global) : %d\n",i); printf ("Address of i : %10p\n",&i); printf ("Value of j (static with no explicit initialization) : %d\n",j); printf ("Address of i : %10p\n",&j); return 0; } I get the output:
end of program (etext) = 0x40067d end of initialized data (edata) = 0x600af0 end of uninitialized data (end) = 0x600af0 ===== Value of i (initialized global) : 42 Address of i : 0x600ae0 Value of j (static with no explicit initialization) : 0 Address of i : 0x600ae8 So i and j are stored at contiguous memory address, between &etext and &edata, which is the regular data section. Furthermore, it seems that &edata == &end which, if I understand correctly, would mean that the BSS is empty.
Now I realize that where the compiler puts which variable is an implementation choice and the results it produces is correct. But I am just wondering why I get that behaviour, and if there is a way to tell gcc to explicitely put such variables in the BSS (I didn't see any obvious solution in the manual).
