Kernel binary size changes in dependence of the gcc version

[Thiemo Seufer <ths@networkno.de>]

Hello All,

I wondered how the various gcc versions influence the size of the
kernel binary, and what difference a size-optimised build makes.

The appended overview is for a Broadcom/Sibyte kernel with some
amount of drivers built in, so the absolute numbers aren't that
relevant. The configuration was always the same except for
CONFIG_64BIT and CONFIG_CC_OPTIMIZE_FOR_SIZE.


Thiemo


32 bit:
-------

Kernel 2.6.17-rc5 Sibyte SWARM 32 bit, default compiler options:

   text	   data	    bss	    dec	    hex	filename
3500246	 319636	 172080	3991962	 3ce99a	vmlinux   # gcc-3.3 (3.3.6-13)
3440510	 291012	 172080	3903602	 3b9072 vmlinux   # gcc-3.4 (3.4.6-1)
3482825	 291140	 172080	3946045	 3c363d vmlinux   # gcc-4.0 (4.0.3-3)
3452750	 288164	 172080	3912994	 3bb522 vmlinux   # gcc-4.1 (4.1.0-4)
3455566	 288164	 172080	3915810	 3bc022 vmlinux   # gcc-snapshot (20060530-1)


Kernel 2.6.17-rc5 Sibyte SWARM 32 bit, size optimized build:

   text	   data	    bss	    dec	    hex	filename
3423398	 319636	 172080	3915114	 3bbd6a	vmlinux   # gcc-3.3 (3.3.6-13)
3224502	 291012	 172080	3687594	 3844aa	vmlinux   # gcc-3.4 (3.4.6-1)

Newer gcc versions fail to build the 2.6.17-rc5 32 bit kernel with 
-Os due to unresolved references to libgcc. With a kernel patch
providing libgcc functions, and a 2.6.17-rc6 snapshot:

   text	   data	    bss	    dec	    hex	filename
3415310	 319620	 172080	3907010	 3b9dc2	vmlinux   # gcc-3.3 (3.3.6-13)
3215829	 290996	 172080	3678905	 3822b9	vmlinux   # gcc-3.4 (3.4.6-1)
3175683	 290404	 172080	3638167	 378397	vmlinux   # gcc-4.0 (4.0.3-3)
3184250	 287348	 172080	3643678	 37991e	vmlinux   # gcc-4.1 (4.1.0-4)
3198118	 287348	 172080	3657546	 37cf4a	vmlinux   # gcc-snapshot (20060530-1)


64 bit:
-------

The difference in size from gcc-3.4 to gcc-4.0 for 64 bit kernels is to
a large part caused by the use of -msym32, which is only available
since gcc-4.0.

Kernel 2.6.17-rc5 Sibyte SWARM 64 bit, default compiler options:

   text	   data	    bss	    dec	    hex	filename
4240626	 506688	 258096	5005410	 4c6062	vmlinux   # gcc-3.3 (3.3.6-13)
4183387	 469024	 258096	4910507	 4aedab	vmlinux   # gcc-3.4 (3.4.6-1)
3740658	 469272	 258096	4468026	 442d3a	vmlinux   # gcc-4.0 (4.0.3-3)
3701722	 463904	 258096	4423722	 43802a	vmlinux   # gcc-4.1 (4.1.0-4)
3703474	 463904	 258096	4425474	 438702	vmlinux   # gcc-snapshot (20060530-1)


Kernel 2.6.17-rc5 Sibyte SWARM 64 bit, size optimized build:

   text	   data	    bss	    dec	    hex	filename
4110677	 506688	 258096	4875461	 4a64c5	vmlinux   # gcc-3.3 (3.3.6-13)
3912126	 469024	 258096	4639246	 46ca0e	vmlinux   # gcc-3.4 (3.4.6-1)
3384418	 468248	 258096	4110762	 3eb9aa	vmlinux   # gcc-4.0 (4.0.3-3)
3389841	 462880	 258096	4110817	 3eb9e1	vmlinux   # gcc-4.1 (4.1.0-4)
3401534	 462880	 258096	4122510	 3ee78e	vmlinux   # gcc-snapshot (20060530-1)