Consider compiling test.c, with this content:
VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
#include "test.h"
int
main (int argc, char **argv)
{
int a = PLUS (1,2);
int b = PLUS (3,4);
return 0;
}
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...where test.h has this content:
VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
extern int foo ();
#define PLUS(A, B) A + B
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The undocumented -fdump-internal-locations option outputs this information
to stderr, showing what each source_location value means. Source code
lines are quoted, showing both per-line source_location values and
per-line&column source_location values (written vertically under the
corresponding character of source code).
VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
RESERVED LOCATIONS
source_location interval: 0 <= loc < 2
ORDINARY MAP: 0
source_location interval: 32 <= loc < 64
file: test.c
starting at line: 1
column bits: 12
range bits: 5
test.c: 1|loc: 32|#include "test.h"
|69269258258148147
|46802468024680246
ORDINARY MAP: 1
source_location interval: 64 <= loc < 96
file: <built-in>
starting at line: 0
column bits: 0
range bits: 0
ORDINARY MAP: 2
source_location interval: 96 <= loc < 128
file: <command-line>
starting at line: 0
column bits: 0
range bits: 0
ORDINARY MAP: 3
source_location interval: 128 <= loc < 160128
file: /usr/include/stdc-predef.h
starting at line: 1
column bits: 12
range bits: 5
(contents of /usr/include/stdc-predef.h snipped for brevity)
ORDINARY MAP: 4
source_location interval: 160128 <= loc < 160160
file: <command-line>
starting at line: 32
column bits: 12
range bits: 5
ORDINARY MAP: 5
source_location interval: 160160 <= loc < 164256
file: test.c
starting at line: 1
column bits: 12
range bits: 5
test.c: 1|loc:160160|#include "test.h"
|00000000000000000
|12223334445556667
|92582581481470470
|24680246802468024
ORDINARY MAP: 6
source_location interval: 164256 <= loc < 173280
file: test.h
starting at line: 1
column bits: 12
range bits: 5
test.h: 1|loc:164256|extern int foo ();
|444444444444444444
|233344455566677788
|825814814704703603
|802468024680246802
test.h: 2|loc:168352|
|
|
|
|
test.h: 3|loc:172448|#define PLUS(A, B) A + B
|222222222222222223333333
|455566677788889990001112
|814704703603692692582581
|024680246802468024680246
ORDINARY MAP: 7
source_location interval: 173280 <= loc < 202016
file: test.c
starting at line: 2
column bits: 12
range bits: 5
test.c: 2|loc:173280|
|
|
|
|
test.c: 3|loc:177376|int
|777
|444
|047
|802
test.c: 4|loc:181472|main (int argc, char **argv)
|1111111111111111222222222222
|5556666777888999000111222333
|0360369269258258148147047036
|4680246802468024680246802468
test.c: 5|loc:185568|{
|5
|6
|0
|0
test.c: 6|loc:189664| int a = PLUS (1,2);
|999999999900000000000
|677788899900011122233
|926925825814814704703
|680246802468024680246
test.c: 7|loc:193760| int b = PLUS (3,4);
|333333344444444444444
|788899900011122233344
|925825814814704703603
|246802468024680246802
test.c: 8|loc:197856| return 0;
|77778888888
|89990001112
|82581481470
|80246802468
test.c: 9|loc:201952|}
|1
|9
|8
|4
UNALLOCATED LOCATIONS
source_location interval: 202016 <= loc < 2147483633
MACRO 1: PLUS (7 tokens)
source_location interval: 2147483633 <= loc < 2147483640
test.c:7:11: note: expansion point is location 194115
int b = PLUS (3,4);
^~~~
map->start_location: 2147483633
macro_locations:
0: 194304, 173088
test.c:7:17: note: token 0 has x-location == 194304
int b = PLUS (3,4);
^
test.c:7:17: note: token 0 has y-location == 173088
1: 173152, 173152
In file included from test.c:1:0:
test.h:3:22: note: token 1 has x-location == y-location == 173152
#define PLUS(A, B) A + B
^
2: 194368, 173216
test.c:7:19: note: token 2 has x-location == 194368
int b = PLUS (3,4);
^
test.c:7:19: note: token 2 has y-location == 173216
3: 0, 2947526575
cc1: note: token 3 has x-location == 0
cc1: note: token 3 has y-location == 2947526575
4: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042942
5: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042942
6: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042942
MACRO 0: PLUS (7 tokens)
source_location interval: 2147483640 <= loc < 2147483647
test.c:6:11: note: expansion point is location 190019
int a = PLUS (1,2);
^~~~
map->start_location: 2147483640
macro_locations:
0: 190208, 173088
test.c:6:17: note: token 0 has x-location == 190208
int a = PLUS (1,2);
^
test.c:6:17: note: token 0 has y-location == 173088
1: 173152, 173152
In file included from test.c:1:0:
test.h:3:22: note: token 1 has x-location == y-location == 173152
#define PLUS(A, B) A + B
^
2: 190272, 173216
test.c:6:19: note: token 2 has x-location == 190272
int a = PLUS (1,2);
^
test.c:6:19: note: token 2 has y-location == 173216
3: 0, 2947526575
cc1: note: token 3 has x-location == 0
cc1: note: token 3 has y-location == 2947526575
4: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042935
5: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042935
6: 2947526575, 2947526575
x-location == y-location == 2947526575 encodes token # 800042935
MAX_SOURCE_LOCATION
source_location interval: 2147483647 <= loc < 2147483648
AD-HOC LOCATIONS
source_location interval: 2147483648 <= loc < 4294967295
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^