Question

In the virtual memory concept, where does C compilers store immediate strings? Example:

char *str = "Immediate string";

Answer 1

gcc at least handles the following four cases differently:

char *globalstr = "immediate global string";
char globalbuf[] = "immediate global array of chars";
int main(int argc, char* argv[]) {
    char *str = "immediate string";
    char buf[] = "immediate array of chars";
    return 0;
}

Local variable char *str and global variable char *str are stored into the .rodata section:

$ readelf --hex-dump=.rodata foo

Hex dump of section '.rodata':
  0x00400688 01000200 696d6d65 64696174 6520676c ....immediate gl
  0x00400698 6f62616c 20737472 696e6700 696d6d65 obal string.imme
  0x004006a8 64696174 65207374 72696e67 00       diate string.

The storage for local variable char buf[] is allocated on the stack at runtime, and initialized via instructions in the .text section:

$ readelf --hex-dump=.text foo

Hex dump of section '.text':
...
  0x00400510 00000048 85c07408 bf480e60 00c9ffe0 ...H..t..H.`....
  0x00400520 c9c39090 554889e5 4883ec50 897dbc48 ....UH..H..P.}.H
  0x00400530 8975b064 488b0425 28000000 488945f8 .u.dH..%(...H.E.
  0x00400540 31c048c7 45c8a406 4000c745 d0696d6d 1.H.E...@..E.imm
  0x00400550 65c745d4 64696174 c745d865 206172c7 e.E.diat.E.e ar.
  0x00400560 45dc7261 7920c745 e06f6620 63c745e4 E.ray .E.of c.E.
  0x00400570 68617273 c645e800 b8000000 00488b55 hars.E.......H.U
  0x00400580 f8644833 14252800 00007405 e897feff .dH3.%(...t.....
...

The global variable char buf[] is stored in the .data section:

$ readelf --hex-dump=.data foo

Hex dump of section '.data':
  0x00601020 00000000 00000000 00000000 00000000 ................
  0x00601030 00000000 00000000 00000000 00000000 ................
  0x00601040 8c064000 00000000 00000000 00000000 ..@.............
  0x00601050 00000000 00000000 00000000 00000000 ................
  0x00601060 696d6d65 64696174 6520676c 6f62616c immediate global
  0x00601070 20617272 6179206f 66206368 61727300  array of chars.