Messages in this thread Patch in this message | | | From | Denys Vlasenko <> | Subject | [PATCH 3/2] section garbage collection for i386 - BONUS TRACK | Date | Wed, 12 Sep 2007 21:45:51 +0100 |
| |
Hi Sam,
This patch makes i386 vmlinux linker script simpler by minimizing number of generated sections.
For example, these sections:
21 .init.text 000204a0 78701000 00701000 00502000 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 22 .init.data 000268db 787214a0 007214a0 005224a0 2**3 CONTENTS, ALLOC, LOAD, DATA 23 .init.setup 00000654 78747d80 00747d80 00548d80 2**2 CONTENTS, ALLOC, LOAD, DATA 24 .initcall.init 000004c4 787483d4 007483d4 005493d4 2**2 CONTENTS, ALLOC, LOAD, DATA 25 .con_initcall.init 00000008 78748898 00748898 00549898 2**2 CONTENTS, ALLOC, LOAD, DATA 26 .altinstructions 00009c23 787488a0 007488a0 005498a0 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 27 .altinstr_replacement 000027de 787524c3 007524c3 005534c3 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 28 .exit.text 00000f31 78754ca4 00754ca4 00555ca4 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 29 .init.ramfs 00000086 78756000 00756000 00557000 2**0 CONTENTS, ALLOC, LOAD, READONLY, DATA
code, data, data, data, rodata, code, code, data... - doesn't look clean.
Can more sanely be grouped like this:
15 .init.text 00023baf 78701000 00701000 00502000 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 16 .init.rodata 00009ca8 78725000 00725000 00526000 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 17 .init.data 00027408 7872eca8 0072eca8 0052fca8 2**3 CONTENTS, ALLOC, LOAD, DATA
All in all, we have 20 sections instead of 32, and it still boots okay.
Full listing:
Before:
$ objdump -h linux-2.6.23-rc4.gc6.t/vmlinux: file format elf32-i386
Sections: Idx Name Size VMA LMA File off Algn 0 .head.text 00000379 78200000 00200000 00001000 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 1 .text 003646da 78200380 00200380 00001380 2**4 CONTENTS, ALLOC, LOAD, READONLY, CODE 2 __ex_table 00000ee8 78564a60 00564a60 00365a60 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 3 .notes 00000024 78565948 00565948 00366948 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 4 .rodata 000e85fe 78566000 00566000 00367000 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 5 .pci_fixup 00000700 7864e600 0064e600 0044f600 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 6 __ksymtab 000057a0 7864ed00 0064ed00 0044fd00 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 7 __ksymtab_gpl 00001ac0 786544a0 006544a0 004554a0 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 8 __ksymtab_gpl_future 00000018 78655f60 00655f60 00456f60 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 9 __kcrctab 00002bd0 78655f78 00655f78 00456f78 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 10 __kcrctab_gpl 00000d60 78658b48 00658b48 00459b48 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 11 __kcrctab_gpl_future 0000000c 786598a8 006598a8 0045a8a8 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 12 __ksymtab_strings 00010d8b 786598b4 006598b4 0045a8b4 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 13 __param 00001838 7866a640 0066a640 0046b640 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 14 .data 0007fe99 7866c000 0066c000 0046d000 2**7 CONTENTS, ALLOC, LOAD, DATA 15 .data_nosave 00001000 786ec000 006ec000 004ed000 2**12 CONTENTS, ALLOC, LOAD, DATA 16 .page_aligned.data 00000800 786ed000 006ed000 004ee000 2**2 CONTENTS, ALLOC, LOAD, DATA 17 .cacheline_aligned.data 0000a000 786ed800 006ed800 004ee800 2**7 CONTENTS, ALLOC, LOAD, DATA 18 .read_mostly.data 000020d0 786f7800 006f7800 004f8800 2**7 CONTENTS, ALLOC, LOAD, DATA 19 .init_task.data 00002000 786fa000 006fa000 004fb000 2**2 CONTENTS, ALLOC, LOAD, DATA 20 .smp_locks 00004798 786fc000 006fc000 004fd000 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 21 .init.text 000204a0 78701000 00701000 00502000 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 22 .init.data 000268db 787214a0 007214a0 005224a0 2**3 CONTENTS, ALLOC, LOAD, DATA 23 .init.setup 00000654 78747d80 00747d80 00548d80 2**2 CONTENTS, ALLOC, LOAD, DATA 24 .initcall.init 000004c4 787483d4 007483d4 005493d4 2**2 CONTENTS, ALLOC, LOAD, DATA 25 .con_initcall.init 00000008 78748898 00748898 00549898 2**2 CONTENTS, ALLOC, LOAD, DATA 26 .altinstructions 00009c23 787488a0 007488a0 005498a0 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 27 .altinstr_replacement 000027de 787524c3 007524c3 005534c3 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 28 .exit.text 00000f31 78754ca4 00754ca4 00555ca4 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 29 .init.ramfs 00000086 78756000 00756000 00557000 2**0 CONTENTS, ALLOC, LOAD, READONLY, DATA 30 .percpu.data 00005f38 78757000 00757000 00558000 2**12 CONTENTS, ALLOC, LOAD, DATA 31 .bss 00047000 7875d000 0075d000 0055df38 2**12 ALLOC 32 .comment 00005004 00000000 00000000 0055df38 2**0 CONTENTS, READONLY
After:
linux-2.6.23-rc4.gc7.t/vmlinux: file format elf32-i386
Sections: Idx Name Size VMA LMA File off Algn 0 .text 00364a5a 78200000 00200000 00001000 2**4 CONTENTS, ALLOC, LOAD, READONLY, CODE 1 __ex_table 00000ee8 78564a60 00564a60 00365a60 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 2 .notes 00000024 78565948 00565948 00366948 2**2 CONTENTS, ALLOC, LOAD, READONLY, CODE 3 .rodata 000e8602 78566000 00566000 00367000 2**3 CONTENTS, ALLOC, LOAD, READONLY, DATA 4 .pci_fixup 00000700 7864e604 0064e604 0044f604 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 5 __ksymtab 000057a0 7864ed04 0064ed04 0044fd04 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 6 __ksymtab_gpl 00001ac0 786544a4 006544a4 004554a4 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 7 __ksymtab_gpl_future 00000018 78655f64 00655f64 00456f64 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 8 __kcrctab 00002bd0 78655f7c 00655f7c 00456f7c 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 9 __kcrctab_gpl 00000d60 78658b4c 00658b4c 00459b4c 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 10 __kcrctab_gpl_future 0000000c 786598ac 006598ac 0045a8ac 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 11 __ksymtab_strings 00010d8b 786598b8 006598b8 0045a8b8 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 12 __param 00001838 7866a644 0066a644 0046b644 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 13 .data 0008f7d0 7866c000 0066c000 0046d000 2**12 CONTENTS, ALLOC, LOAD, DATA 14 .smp_locks 00004798 786fc000 006fc000 004fd000 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 15 .init.text 00023baf 78701000 00701000 00502000 2**0 CONTENTS, ALLOC, LOAD, READONLY, CODE 16 .init.rodata 00009ca8 78725000 00725000 00526000 2**2 CONTENTS, ALLOC, LOAD, READONLY, DATA 17 .init.data 00027408 7872eca8 0072eca8 0052fca8 2**3 CONTENTS, ALLOC, LOAD, DATA 18 .percpu.data 00005f38 78757000 00757000 00558000 2**12 CONTENTS, ALLOC, LOAD, DATA 19 .bss 00047000 7875d000 0075d000 0055df38 2**12 ALLOC 20 .comment 00005004 00000000 00000000 0055df38 2**0 CONTENTS, READONLY
Patch is run-tested.
It's purely cleanup work, it's not bringing any noticeable size wins (well, maybe statistically it will have a bit less alignment padding because I placed together a few page-aligned chunks, but that's all).
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com> -- vda diff -urpN linux-2.6.23-rc4.gc6/arch/i386/kernel/vmlinux.lds.S linux-2.6.23-rc4.gc7/arch/i386/kernel/vmlinux.lds.S --- linux-2.6.23-rc4.gc6/arch/i386/kernel/vmlinux.lds.S 2007-09-12 19:51:42.000000000 +0100 +++ linux-2.6.23-rc4.gc7/arch/i386/kernel/vmlinux.lds.S 2007-09-12 21:10:38.000000000 +0100 @@ -6,7 +6,19 @@ * at run time. Absolute symbols are not relocated. If symbol value should * change if kernel is relocated, make the symbol section relative * by putting it inside the section definition. + * + * Try to avoid creating output sections needlessly. + * Group pieces with same attributes (ro/rw, code/data, + * persistent/discarded-after-init) together in one section. + * + * Statistically, padding is smaller if input sections + * within output section are sorted by alignment in descending order. + * + * If you need to ALIGN a section, putting ALIGN immediately before section + * can result in smaller on-disk image than when you put it immeadiately + * after section's opening '{'. */ + #define LOAD_OFFSET __PAGE_OFFSET #include <asm-generic/vmlinux.lds.h> @@ -18,6 +30,7 @@ OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386") OUTPUT_ARCH(i386) ENTRY(phys_startup_32) + jiffies = jiffies_64; PHDRS { @@ -30,13 +43,11 @@ SECTIONS . = LOAD_OFFSET + LOAD_PHYSICAL_ADDR; phys_startup_32 = startup_32 - LOAD_OFFSET; - .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) { - _text = .; /* Text and read-only data */ - KEEP(*(.head.text)) - } :text = 0x9090 - /* read-only */ .text : AT(ADDR(.text) - LOAD_OFFSET) { + _text = .; /* Text and read-only data */ + KEEP(*(.head.text)) + TEXT_TEXT SCHED_TEXT LOCK_TEXT @@ -54,6 +65,7 @@ SECTIONS __stop___ex_table = .; } + /* Hm? NOTES end up marked as CODE in vmlinux, but they are not. FIXME */ NOTES :text :note BUG_TABLE :text @@ -69,45 +81,39 @@ SECTIONS RODATA /* writeable */ - . = ALIGN(4096); + . = ALIGN(THREAD_SIZE); /* at least 4k */ .data : AT(ADDR(.data) - LOAD_OFFSET) { /* Data */ - DATA_DATA - CONSTRUCTORS - } :data + /* init_task */ + *(.init_task.data) - . = ALIGN(4096); - .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) { + . = ALIGN(4096); + *(.page_aligned.data) + + . = ALIGN(4096); __nosave_begin = .; /* No need to KEEP */ *(.nosave.data) . = ALIGN(4096); __nosave_end = .; - } - . = ALIGN(4096); - .page_aligned.data : AT(ADDR(.page_aligned.data) - LOAD_OFFSET) { - *(.page_aligned.data) + /* The IDT has to be page-aligned because of F0 0F bug */ *(.idt.data) - } - . = ALIGN(32); - .cacheline_aligned.data : AT(ADDR(.cacheline_aligned.data) - LOAD_OFFSET) { + DATA_DATA + CONSTRUCTORS + + . = ALIGN(32); *(.cacheline_aligned.data) - } - /* rarely changed data like cpu maps */ - . = ALIGN(32); - .read_mostly.data : AT(ADDR(.read_mostly.data) - LOAD_OFFSET) { + /* rarely changed data like cpu maps */ + . = ALIGN(32); *(.read_mostly.data) - _edata = .; /* End of data section */ - } - . = ALIGN(THREAD_SIZE); /* init_task */ - .init_task.data : AT(ADDR(.init_task.data) - LOAD_OFFSET) { - *(.init_task.data) - } + _edata = .; + } :data + + /* Might get freed after init */ - /* might get freed after init */ . = ALIGN(4096); .smp_locks : AT(ADDR(.smp_locks) - LOAD_OFFSET) { __smp_locks = .; @@ -116,75 +122,80 @@ SECTIONS } /* Will be freed after init */ - /* Init code and data */ + . = ALIGN(4096); .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) { __init_begin = .; _sinittext = .; *(.init.text) _einittext = .; + + /* No need to KEEP - referenced by .altinstructions */ + *(.altinstr_replacement) + + /* .exit.text is discarded at runtime, not link time, to deal with references + from .altinstructions and .eh_frame */ + *(.exit.text) + } + + /* ro, code */ + SECURITY_INIT + +#if defined(CONFIG_BLK_DEV_INITRD) + /* ALIGN outside section may make on-disk image smaller */ + . = ALIGN(4096); +#endif + .init.rodata : AT(ADDR(.init.rodata) - LOAD_OFFSET) { +#if defined(CONFIG_BLK_DEV_INITRD) + __initramfs_start = .; + KEEP(*(.init.ramfs)) + __initramfs_end = .; +#endif + . = ALIGN(4); + __alt_instructions = .; + KEEP(*(.altinstructions)) + __alt_instructions_end = .; + + . = ALIGN(4); + __parainstructions = .; + KEEP(*(.parainstructions)) + __parainstructions_end = .; } - .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { *(.init.data) } - . = ALIGN(16); - .init.setup : AT(ADDR(.init.setup) - LOAD_OFFSET) { + + .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { + *(.init.data) + + . = ALIGN(16); __setup_start = .; /* __setup_param() macro produces these, * obsolete_checksetup() processes them */ KEEP(*(.init.setup)) __setup_end = .; - } - .initcall.init : AT(ADDR(.initcall.init) - LOAD_OFFSET) { + __initcall_start = .; INITCALLS __initcall_end = .; - } - .con_initcall.init : AT(ADDR(.con_initcall.init) - LOAD_OFFSET) { + __con_initcall_start = .; KEEP(*(.con_initcall.init)) __con_initcall_end = .; - } - SECURITY_INIT - . = ALIGN(4); - .altinstructions : AT(ADDR(.altinstructions) - LOAD_OFFSET) { - __alt_instructions = .; - KEEP(*(.altinstructions)) - __alt_instructions_end = .; - } - .altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) { - /* No need to KEEP - referenced by .altinstructions */ - *(.altinstr_replacement) - } - . = ALIGN(4); - .parainstructions : AT(ADDR(.parainstructions) - LOAD_OFFSET) { - __parainstructions = .; - KEEP(*(.parainstructions)) - __parainstructions_end = .; - } - /* .exit.text is discarded at runtime, not link time, to deal with references - from .altinstructions and .eh_frame */ - .exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) { *(.exit.text) } - .exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) { *(.exit.data) } -#if defined(CONFIG_BLK_DEV_INITRD) - . = ALIGN(4096); - .init.ramfs : AT(ADDR(.init.ramfs) - LOAD_OFFSET) { - __initramfs_start = .; - KEEP(*(.init.ramfs)) - __initramfs_end = .; + /* TODO: can .exit.data be discarded at link time? */ + *(.exit.data) } -#endif . = ALIGN(4096); .percpu.data : AT(ADDR(.percpu.data) - LOAD_OFFSET) { __per_cpu_start = .; - *(.percpu.data) + *(SORT_BY_ALIGNMENT(.percpu.data)) + /* Dont move in front of .percpu.data, .percpu.data contains page-aligned stuff */ *(.percpu.shared_aligned.data) __per_cpu_end = .; } - . = ALIGN(4096); /* End of "freed after init" portion */ + . = ALIGN(4096); .bss : AT(ADDR(.bss) - LOAD_OFFSET) { __init_end = .; __bss_start = .; /* BSS */ | |