Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161372AbWHALRF (ORCPT ); Tue, 1 Aug 2006 07:17:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161371AbWHALQx (ORCPT ); Tue, 1 Aug 2006 07:16:53 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:4317 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S932651AbWHALFr (ORCPT ); Tue, 1 Aug 2006 07:05:47 -0400 From: "Eric W. Biederman" To: Cc: , Horms , Jan Kratochvil , "H. Peter Anvin" , Magnus Damm , Vivek Goyal , Linda Wang , "Eric W. Biederman" Subject: [PATCH 1/33] i386: vmlinux.lds.S Distinguish absolute symbols Date: Tue, 1 Aug 2006 05:03:16 -0600 Message-Id: <11544302283864-git-send-email-ebiederm@xmission.com> X-Mailer: git-send-email 1.4.2.rc2.g5209e In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7920 Lines: 268 Ld knows about 2 kinds of symbols, absolute and section relative. Section relative symbols symbols change value when a section is moved and absolute symbols do not. Currently in the linker script we have several labels marking the beginning and ending of sections that are outside of sections, making them absolute symbols. Having a mixture of absolute and section relative symbols refereing to the same data is currently harmless but it is confusing. This must be done carefully as newer revs of ld do not place symbols that appear in sections without data and instead ld makes those symbols global :( My ultimate goal is to build a relocatable kernel. The safest and least intrusive technique is to generate relocation entries so the kernel can be relocated at load time. The only penalty would be an increase in the size of the kernel binary. The problem is that if absolute and relocatable symbols are not properly specified absolute symbols will be relocated or section relative symbols won't be, which is fatal. The practical motivation is that when generating kernels that will run from a reserved area for analyzing what caused a kernel panic, it is simpler if you don't need to hard code the physical memory location they will run at, especially for the distributions. Signed-off-by: Eric W. Biederman --- arch/i386/kernel/vmlinux.lds.S | 111 ++++++++++++++++++++----------------- include/asm-generic/vmlinux.lds.h | 2 - 2 files changed, 60 insertions(+), 53 deletions(-) diff --git a/arch/i386/kernel/vmlinux.lds.S b/arch/i386/kernel/vmlinux.lds.S index 2d4f138..db0833b 100644 --- a/arch/i386/kernel/vmlinux.lds.S +++ b/arch/i386/kernel/vmlinux.lds.S @@ -18,43 +18,46 @@ SECTIONS . = __KERNEL_START; phys_startup_32 = startup_32 - LOAD_OFFSET; /* read-only */ - _text = .; /* Text and read-only data */ .text : AT(ADDR(.text) - LOAD_OFFSET) { + _text = .; /* Text and read-only data */ *(.text) SCHED_TEXT LOCK_TEXT KPROBES_TEXT *(.fixup) *(.gnu.warning) - } = 0x9090 - - _etext = .; /* End of text section */ + _etext = .; /* End of text section */ + } = 0x9090 . = ALIGN(16); /* Exception table */ - __start___ex_table = .; - __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { *(__ex_table) } - __stop___ex_table = .; + __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { + __start___ex_table = .; + *(__ex_table) + __stop___ex_table = .; + } RODATA . = ALIGN(4); - __tracedata_start = .; .tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) { + __tracedata_start = .; *(.tracedata) + __tracedata_end = .; } - __tracedata_end = .; /* writeable */ .data : AT(ADDR(.data) - LOAD_OFFSET) { /* Data */ *(.data) CONSTRUCTORS - } + } . = ALIGN(4096); - __nosave_begin = .; - .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) { *(.data.nosave) } - . = ALIGN(4096); - __nosave_end = .; + .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) { + __nosave_begin = .; + *(.data.nosave) + . = ALIGN(4096); + __nosave_end = .; + } . = ALIGN(4096); .data.page_aligned : AT(ADDR(.data.page_aligned) - LOAD_OFFSET) { @@ -68,8 +71,10 @@ SECTIONS /* rarely changed data like cpu maps */ . = ALIGN(32); - .data.read_mostly : AT(ADDR(.data.read_mostly) - LOAD_OFFSET) { *(.data.read_mostly) } - _edata = .; /* End of data section */ + .data.read_mostly : AT(ADDR(.data.read_mostly) - LOAD_OFFSET) { + *(.data.read_mostly) + _edata = .; /* End of data section */ + } #ifdef CONFIG_STACK_UNWIND . = ALIGN(4); @@ -87,39 +92,41 @@ #endif /* might get freed after init */ . = ALIGN(4096); - __smp_alt_begin = .; - __smp_alt_instructions = .; .smp_altinstructions : AT(ADDR(.smp_altinstructions) - LOAD_OFFSET) { + __smp_alt_begin = .; + __smp_alt_instructions = .; *(.smp_altinstructions) + __smp_alt_instructions_end = .; } - __smp_alt_instructions_end = .; . = ALIGN(4); - __smp_locks = .; .smp_locks : AT(ADDR(.smp_locks) - LOAD_OFFSET) { + __smp_locks = .; *(.smp_locks) + __smp_locks_end = .; } - __smp_locks_end = .; .smp_altinstr_replacement : AT(ADDR(.smp_altinstr_replacement) - LOAD_OFFSET) { *(.smp_altinstr_replacement) + . = ALIGN(4096); + __smp_alt_end = .; } - . = ALIGN(4096); - __smp_alt_end = .; /* will be freed after init */ . = ALIGN(4096); /* Init code and data */ - __init_begin = .; .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) { + __init_begin = .; _sinittext = .; *(.init.text) _einittext = .; } .init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { *(.init.data) } . = ALIGN(16); - __setup_start = .; - .init.setup : AT(ADDR(.init.setup) - LOAD_OFFSET) { *(.init.setup) } - __setup_end = .; - __initcall_start = .; + .init.setup : AT(ADDR(.init.setup) - LOAD_OFFSET) { + __setup_start = .; + *(.init.setup) + __setup_end = .; + } .initcall.init : AT(ADDR(.initcall.init) - LOAD_OFFSET) { + __initcall_start = .; *(.initcall1.init) *(.initcall2.init) *(.initcall3.init) @@ -127,20 +134,20 @@ #endif *(.initcall5.init) *(.initcall6.init) *(.initcall7.init) + __initcall_end = .; } - __initcall_end = .; - __con_initcall_start = .; .con_initcall.init : AT(ADDR(.con_initcall.init) - LOAD_OFFSET) { + __con_initcall_start = .; *(.con_initcall.init) + __con_initcall_end = .; } - __con_initcall_end = .; SECURITY_INIT . = ALIGN(4); - __alt_instructions = .; .altinstructions : AT(ADDR(.altinstructions) - LOAD_OFFSET) { + __alt_instructions = .; *(.altinstructions) + __alt_instructions_end = .; } - __alt_instructions_end = .; .altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) { *(.altinstr_replacement) } @@ -149,32 +156,32 @@ #endif .exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) { *(.exit.text) } .exit.data : AT(ADDR(.exit.data) - LOAD_OFFSET) { *(.exit.data) } . = ALIGN(4096); - __initramfs_start = .; - .init.ramfs : AT(ADDR(.init.ramfs) - LOAD_OFFSET) { *(.init.ramfs) } - __initramfs_end = .; + .init.ramfs : AT(ADDR(.init.ramfs) - LOAD_OFFSET) { + __initramfs_start = .; + *(.init.ramfs) + __initramfs_end = .; + } . = ALIGN(L1_CACHE_BYTES); - __per_cpu_start = .; - .data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) { *(.data.percpu) } - __per_cpu_end = .; + .data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) { + __per_cpu_start = .; + *(.data.percpu) + __per_cpu_end = .; + } . = ALIGN(4096); - __init_end = .; /* freed after init ends here */ - __bss_start = .; /* BSS */ - .bss.page_aligned : AT(ADDR(.bss.page_aligned) - LOAD_OFFSET) { - *(.bss.page_aligned) - } .bss : AT(ADDR(.bss) - LOAD_OFFSET) { + __init_end = .; + __bss_start = .; /* BSS */ + *(.bss.page_aligned) *(.bss) + . = ALIGN(4); + __bss_stop = .; + _end = . ; + /* This is where the kernel creates the early boot page tables */ + . = ALIGN(4096); + pg0 = . ; } - . = ALIGN(4); - __bss_stop = .; - - _end = . ; - - /* This is where the kernel creates the early boot page tables */ - . = ALIGN(4096); - pg0 = .; /* Sections to be discarded */ /DISCARD/ : { diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index db5a373..7cd3c22 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -11,8 +11,8 @@ #define ALIGN_FUNCTION() . = ALIGN(8) #define RODATA \ . = ALIGN(4096); \ - __start_rodata = .; \ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ + VMLINUX_SYMBOL(__start_rodata) = .; \ *(.rodata) *(.rodata.*) \ *(__vermagic) /* Kernel version magic */ \ } \ -- 1.4.2.rc2.g5209e - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/