gold - Addresses of zero-initialized globals are not shown in Mapfile

[Koehrer Mathias (ETAS/ESW5)]

> Hi all,
> 
> In a project we switched from "ld" to "gold". The performance is great!
> Version of gold:
> GNU gold (GNU Binutils for Debian 2.25) 1.11
> 
> However there is one issue I want to solve:
> I do not see the addresses of global zero initialized variables in the map file!
> 
> Example:
> I have the following tiny C-source code (t.c):
> 
> int global_zero;
> int global_one = 1;
> int main(void)
> {
>     return 0;
> }
> 
> I compile this on a Linux x86-64 (amd64) machine:
> gcc -Wl,-fuse-ld=gold -Xlinker -Map=Mapfile t.c In the Mapfile I can see the
> following:
> -----------------------------------------------------
> ...
> Allocating common symbols
> Common symbol       size              file
> 
> global_zero         0x4               /tmp/cc3JpgFt.o
> ...
>  .data          0x0000000000401930        0x4 /tmp/cc3JpgFt.o
>                    0x0000000000401930                global_one
>  .data          0x0000000000401934        0x0 /usr/lib/x86_64-linux-
> gnu/libc_nonshared.a(elf-init.oS)
> ...
> -----------------------------------------------------
> 
> The address of global_one is shown, the address of global_zero is not shown!
> 
> 
> 
> When I compile the same code using the linker "ld":
> gcc -Wl,-fuse-ld=gold -Xlinker -Map=Mapfile t.c I got the following information in the
> Mapfile:
Typo: Must be
gcc -Xlinker -Map=Mapfile t.c

> -----------------------------------------------------
> ...
> Allocating common symbols
> Common symbol       size              file
> 
> global_zero         0x4               /tmp/ccjPds2R.o
> ...
> .data                0x00000000006008a8        0x4 /tmp/ccjPds2R.o
>                         0x00000000006008a8                global_one
> ...
> 
>  *(COMMON)
>  *fill*                0x00000000006008ad       0x3
>  COMMON    0x00000000006008b0        0x4 /tmp/ccjPds2R.o
>                        0x00000000006008b0                global_zero
> ...
> -----------------------------------------------------
> 
> Here I can see both addresses of global_one and global_zero.
> 
> My question is now:
> How can I force the "gold" linker to output also the address of the zero-initialized
> variables?
> Is there any command line argument I can use for that?
> 
> Thanks for any feedback on this question:
> 
> 
> Best regards
> 
> Mathias
>