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Re: [Gm2] Minimal libraries

From: Gaius Mulley
Subject: Re: [Gm2] Minimal libraries
Date: Tue, 30 Jun 2009 15:56:05 +0100
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)

Waldek Hebisch <address@hidden> writes:

> Gaius Mulley wrote:
>> address@hidden writes:
>> > Gnu C, Gnu C++, and Critical Mass Modula 3 all produce "hello world"
>> > binaries of 6-8Kb stripped, where Gnu Modula 2 produces 110Kb stripped.
>> > I doubt that the differences are due to lack of link time optimisations,
>> > tho' they may be.  Anyway, thanks.
>> >
>> > Will
>> Hi,
>> C, C++ and gm2 all use the same middle and backend.  The difference is
>> the way the libraries are organised.  For example glibc is composed of
>> 6244 C files, most of which consist of one function per object, thus
>> when linking against glibc.a the linker pulls in only an object
>> matching a function, (hence a pretty minimal binary).
> The last time I tried _statically_ linking with glibc gave me about
> 90 kb.  I think that days of 4kb static executables are gone, all
> really small "hello world" programs from Gnu use dynamically
> linked libraries.
> It is possible to get some link optimizations with current compiler.
> IIRC the '-ffunction-sections' option to the compiler marks function
> boundaries in the object files, so that with proper linker option
> one can link in only needed functions.  However, few years ago
> (when I checked this) linker could do this only for completely
> static build.  So the price was static linking to glibc, bringing
> about 90 kb of routines from there and defeating the purpose.
> New release of binutils was supposed to fix problem of mixing
> per-function sections and shared libraries, so anybody interested
> should probably re-check.

Hi Waldek,

many thanks for the pointers to these flags.  I've now enabled
-ffunction-sections -fdata-sections when building all libraries.
Linking the standard hello world example gives the following sized

$ gm2 -c -g -I. -ffunction-sections -fdata-sections  hello.mod
$ gm2  -g -I. -ffunction-sections -fdata-sections  hello.mod -Wl,--gc-sections

$ size a.out
   text    data     bss     dec     hex filename
  63780     808   10088   74676   123b4 a.out

$ gm2 -c -g -I. -ffunction-sections -fdata-sections  hello.mod -fno-exceptions
$ gm2  -g -I. -ffunction-sections -fdata-sections  hello.mod -Wl,--gc-sections 
$ size a.out
   text    data     bss     dec     hex filename
  44679     728    9552   54959    d6af a.out

definitely an improvement and I suspect more options might remove
further dead code..


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