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)
