Re: [RFC][PATCH 0/5] kbuild changes, thin archives, --gc-sections

[Nicholas Piggin]

On Fri,  5 Aug 2016 22:11:58 +1000
Nicholas Piggin <npig...@gmail.com> wrote:

> Hello,
> 
> I have 3 different things in this patchset. All arch specific, but all
> involve kbuild changes, so I'd like to discuss them with kbuild
> maintainers. The goal has been to improve long standing linking
> difficulties with the powerpc kernel.

Here's a 30 second hack of an x86 patch. It seems to build and
boot defconfig in a really quick kvm test.

For x86-64 machine building x86 target, defconfig,

make -j8 vmlinux time:
              orig      thinarc   thinarc+dce
real     4m58.865s    4m59.747s     5m20.028s
user    15m14.428s   15m13.868s    15m17.012s
sys      0m57.296s    0m55.904s     0m58.416s

build output directory size:
              orig      thinarc   thinarc+dce
              317M         257M          285M

vmlinux size:
    text     data      bss       dec   filename
10192338  4360136  1105920  15658394   vmlinux
10186739  4356040  1105920  15648699   vmlinux.thinarc
 9580486  3759880  1011712  14352078   vmlinux.thinarc+dce

Thanks,
Nick


diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0a7b885..845069e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -51,6 +51,8 @@ config X86
        select ARCH_WANT_IPC_PARSE_VERSION      if X86_32
        select ARCH_WANT_OPTIONAL_GPIOLIB
        select BUILDTIME_EXTABLE_SORT
+       select THIN_ARCHIVES
+       select LINKER_DCE
        select CLKEVT_I8253
        select CLKSRC_I8253                     if X86_32
        select CLOCKSOURCE_VALIDATE_LAST_CYCLE
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 9297a00..7395dd8 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -92,7 +92,7 @@ SECTIONS
        .text :  AT(ADDR(.text) - LOAD_OFFSET) {
                _text = .;
                /* bootstrapping code */
-               HEAD_TEXT
+               KEEP(HEAD_TEXT)
                . = ALIGN(8);
                _stext = .;
                TEXT_TEXT
@@ -321,7 +321,7 @@ SECTIONS
        .bss : AT(ADDR(.bss) - LOAD_OFFSET) {
                __bss_start = .;
                *(.bss..page_aligned)
-               *(.bss)
+               *(.bss .bss.*)
                . = ALIGN(PAGE_SIZE);
                __bss_stop = .;
        }