Program size, linking matter, and static this()

[Marco Leise]

I tried different versions of DMD 2.057:
- compiled from sources in the release zip (Gentoo ebuild)
- using the 32-bit binaries in the release zip
- compiling the latest 32-bit version of DMD from the repository
I tried different compiler flags or no flags at all, compiled similar code  
in C++ to see if the linker is ok and tried -m32 and -m64, all to no  
avail. Then I found a solution that I can hardly imagine happening only on  
my unique snow-flake of a system ;) :

struct Test {
     __gshared byte abcd[10 * 1024 * 1024];
}

If it weren't for your own test results, I'd assume there is a small  
compiler bug in the code that decides what can go into .bss, that makes it  
look only for data explicitly flagged as __gshared, but not other  
immutable data. (Something like that anyway.)
I back-tracked the compiler code to where it either calls obj_bytes (good  
case, goes into .bss) or obj_lidata (bad case) to write the 10 MB of  
zeros. But there were so many call sites, that I figured someone with  
inside knowledge would figure it out faster.

As a side-effect of this experiment I found this combination to do funny  
things at runtime:

--------------------------------------------------

struct Test {
	byte arr1[1024 * 1024 * 10];
	__gshared byte arr2[1024 * 1024 * 10];
}

int main() {
	Test test;
	return 0;
}

--------------------------------------------------

-- Marco

Am 18.01.2012, 11:18 Uhr, schrieb Walter Bright  
<newshound2 at digitalmars.com>:

> On 1/18/2012 1:43 AM, Marco Leise wrote:
>> It is back again! The following struct in my main module increases the
>> executable size by 10MB with DMD 2.075:
>>
>> struct Test {
>> byte abcd[10 * 1024 * 1024];
>> }
>
> Compiling it and obj2asm'ing the result, and you'll see it goes into the  
> BSS segment:
>
>
> _TEXT   segment dword use32 public 'CODE'       ;size is 0
> _TEXT   ends
> _DATA   segment para use32 public 'DATA'        ;size is 12
> _DATA   ends
> CONST   segment para use32 public 'CONST'       ;size is 0
> CONST   ends
> _BSS    segment para use32 public 'BSS' ;size is 10485760
> _BSS    ends
> FLAT    group
>          extrn   _D19TypeInfo_S3foo4Test6__initZ
>
>          public  _D3foo4Test6__initZ
> FMB     segment dword use32 public 'DATA'       ;size is 0
> FMB     ends
> FM      segment dword use32 public 'DATA'       ;size is 4
> FM      ends
> FME     segment dword use32 public 'DATA'       ;size is 0
> FME     ends
>          extrn   _D15TypeInfo_Struct6__vtblZ
>
>          public  _D3foo12__ModuleInfoZ
> _D19TypeInfo_S3foo4Test6__initZ COMDAT flags=x0 attr=x10 align=x0
>
> _TEXT   segment
>          assume  CS:_TEXT
> _TEXT   ends
> _DATA   segment
> _D3foo12__ModuleInfoZ:
>          db      004h,000h,000h,0ffffff80h,000h,000h,000h,000h    
> ;........
>          db      066h,06fh,06fh,000h     ;foo.
> _DATA   ends
> CONST   segment
> CONST   ends
> _BSS    segment
> _BSS    ends
> FMB     segment
> FMB     ends
> FM      segment
>          dd      offset FLAT:_D3foo12__ModuleInfoZ
> FM      ends
> FME     segment
> FME     ends
> _D19TypeInfo_S3foo4Test6__initZ comdat
>          dd      offset FLAT:_D15TypeInfo_Struct6__vtblZ
>          db      000h,000h,000h,000h     ;....
>          db      008h,000h,000h,000h     ;....
>          dd      offset FLAT:_D19TypeInfo_S3foo4Test6__initZ[03Ch]
>          db      000h,000h,0ffffffa0h,000h,000h,000h,000h,000h    
> ;........
>          db      000h,000h,000h,000h,000h,000h,000h,000h ;........
>          db      000h,000h,000h,000h,000h,000h,000h,000h ;........
>          db      000h,000h,000h,000h,000h,000h,000h,000h ;........
>          db      000h,000h,000h,000h,000h,000h,000h,000h ;........
>          db      001h,000h,000h,000h,066h,06fh,06fh,02eh ;....foo.
>          db      054h,065h,073h,074h,000h        ;Test.
> _D19TypeInfo_S3foo4Test6__initZ ends
>          end
> -------------------------------------------------
>
> Adding a void main(){} yields an executable of 145,948 bytes.