Hi. 2017-06-01 6:13 GMT+09:00 Arnd Bergmann <arnd@xxxxxxxx>: > On Mon, May 29, 2017 at 10:11 AM, Nicholas Piggin <npiggin@xxxxxxxxx> wrote: >> Supporting two different intermediate-artifact packaging schemes >> was only ever intended as a temporary transition. >> >> This has so far caused no problems for powerpc, after a small fix >> for how the arch invoked ar. So now allow any arch to select the >> option, continue defaulting to N. >> >> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> >> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> >> --- >> The next step will be to have archs always select THIN_ARCHIVES >> when they are known to work. Then remove the option entirely. >> >> x86 has always just worked for me, so that should be easy. > > I have build-tested many thousand randconfig kernels on arm32 with > this option enabled, and did not run into build-time regressions > besides some initial problems from a broken binutils snapshot > (all released binutils versions should be fine). > Please let me mention two advantages of using THIN_ARCHIVES. [1] By switching to CONFIG_THIN_ARCHIVES, we can get back building allyesconfig on ARM. (probably because the final link is given more flexibility to insert veneers) This is a much cleaner solution than the following patch: https://patchwork.kernel.org/patch/6120441/ [2] Thick archive does not work well with garbage collection (CONFIG_LD_DEAD_CODE_DATA_ELIMINATION). CONFIG_LD_DEAD_CODE_DATA_ELIMINATION can not deal with static functions with the same function name. The following is the test code I played with. diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3dcd7ec..a267145 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -13,6 +13,7 @@ config ARM64 select ARCH_HAS_ELF_RANDOMIZE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_GIGANTIC_PAGE + select LD_DEAD_CODE_DATA_ELIMINATION select ARCH_HAS_KCOV select ARCH_HAS_SET_MEMORY select ARCH_HAS_SG_CHAIN --- a/init/main.c +++ b/init/main.c @@ -485,6 +485,8 @@ static void __init mm_init(void) ioremap_huge_init(); } +void this_is_called(void); + asmlinkage __visible void __init start_kernel(void) { char *command_line; @@ -676,6 +678,9 @@ asmlinkage __visible void __init start_kernel(void) } /* Do the rest non-__init'ed, we're now alive */ + + this_is_called(); + rest_init(); } diff --git a/kernel/Makefile b/kernel/Makefile index 72aa080..b938d4e 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -9,7 +9,8 @@ obj-y = fork.o exec_domain.o panic.o \ extable.o params.o \ kthread.o sys_ni.o nsproxy.o \ notifier.o ksysfs.o cred.o reboot.o \ - async.o range.o smpboot.o ucount.o + async.o range.o smpboot.o ucount.o \ + foo.o bar.o obj-$(CONFIG_MULTIUSER) += groups.o diff --git a/kernel/bar.c b/kernel/bar.c new file mode 100644 index 0000000..3b1431e --- /dev/null +++ b/kernel/bar.c @@ -0,0 +1,31 @@ +#include <linux/printk.h> + +static void greeting(void) +{ + printk("hello world0\n"); + printk("hello world1\n"); + printk("hello world2\n"); + printk("hello world3\n"); + printk("hello world4\n"); + printk("hello world5\n"); + printk("hello world6\n"); + printk("hello world7\n"); + printk("hello world8\n"); + printk("hello world9\n"); +} + +void this_is_not_called1(void) +{ + int i; + + for (i = 0; i < 100; i++) + greeting(); +} + +void this_is_not_called2(void) +{ + int i; + + for (i = 0; i < 1000; i++) + greeting(); +} diff --git a/kernel/foo.c b/kernel/foo.c new file mode 100644 index 0000000..10c8e8b --- /dev/null +++ b/kernel/foo.c @@ -0,0 +1,31 @@ +#include <linux/printk.h> + +static void greeting(void) +{ + printk("goodbye world0\n"); + printk("goodbye world1\n"); + printk("goodbye world2\n"); + printk("goodbye world3\n"); + printk("goodbye world4\n"); + printk("goodbye world5\n"); + printk("goodbye world6\n"); + printk("goodbye world7\n"); + printk("goodbye world8\n"); + printk("goodbye world9\n"); +} + +void this_is_called(void) +{ + int i; + + for (i = 0; i < 100; i++) + greeting(); +} + +void this_is_not_called0(void) +{ + int i; + + for (i = 0; i < 1000; i++) + greeting(); +} The function greeting() in kernel/foo.c is called, whereas greeting() in kernel/bar.c is not called. The latter should be removed from the final binary, but both are kept. $ aarch64-linux-gnu-nm vmlinux | grep 'greeting\|this_is_' ffff0000080f7420 t greeting ffff0000080f74a8 t greeting ffff0000080f7530 T this_is_called By selecting CONFIG_THIN_ARCHIVES, greeting() in kernel/bar.c is removed correctly. $ aarch64-linux-gnu-nm vmlinux | grep 'greeting\|this_is_' ffff0000080f2bf0 t greeting ffff0000080f2c78 T this_is_called -- Best Regards Masahiro Yamada
