Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030349AbWJCRbB (ORCPT ); Tue, 3 Oct 2006 13:31:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030348AbWJCRal (ORCPT ); Tue, 3 Oct 2006 13:30:41 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:62100 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S1030349AbWJCRaf (ORCPT ); Tue, 3 Oct 2006 13:30:35 -0400 Date: Tue, 3 Oct 2006 13:04:13 -0400 From: Vivek Goyal To: linux kernel mailing list Cc: Reloc Kernel List , ebiederm@xmission.com, akpm@osdl.org, ak@suse.de, horms@verge.net.au, lace@jankratochvil.net, hpa@zytor.com, magnus.damm@gmail.com, lwang@redhat.com, dzickus@redhat.com, maneesh@in.ibm.com Subject: [PATCH 1/12] i386: Distinguish absolute symbols Message-ID: <20061003170413.GA3164@in.ibm.com> Reply-To: vgoyal@in.ibm.com References: <20061003170032.GA30036@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061003170032.GA30036@in.ibm.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8560 Lines: 276 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 Signed-off-by: Vivek Goyal --- arch/i386/kernel/vmlinux.lds.S | 109 ++++++++++++++++++++------------------ include/asm-generic/vmlinux.lds.h | 4 - 2 files changed, 60 insertions(+), 53 deletions(-) diff -puN arch/i386/kernel/vmlinux.lds.S~i386-vmlinux.lds.S-Distinguish-absolute-symbols arch/i386/kernel/vmlinux.lds.S --- linux-2.6.18-git17/arch/i386/kernel/vmlinux.lds.S~i386-vmlinux.lds.S-Distinguish-absolute-symbols 2006-10-02 13:17:58.000000000 -0400 +++ linux-2.6.18-git17-root/arch/i386/kernel/vmlinux.lds.S 2006-10-02 14:38:44.000000000 -0400 @@ -24,31 +24,32 @@ 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) - } :text = 0x9090 - - _etext = .; /* End of text section */ + _etext = .; /* End of text section */ + } :text = 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 */ @@ -57,10 +58,12 @@ SECTIONS } :data . = 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) { @@ -74,8 +77,10 @@ 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); @@ -93,39 +98,41 @@ SECTIONS /* 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) @@ -133,20 +140,20 @@ SECTIONS *(.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) } @@ -155,32 +162,32 @@ SECTIONS .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 -puN include/asm-generic/vmlinux.lds.h~i386-vmlinux.lds.S-Distinguish-absolute-symbols include/asm-generic/vmlinux.lds.h --- linux-2.6.18-git17/include/asm-generic/vmlinux.lds.h~i386-vmlinux.lds.S-Distinguish-absolute-symbols 2006-10-02 13:17:58.000000000 -0400 +++ linux-2.6.18-git17-root/include/asm-generic/vmlinux.lds.h 2006-10-02 13:17:58.000000000 -0400 @@ -11,8 +11,8 @@ #define RODATA \ . = ALIGN(4096); \ - __start_rodata = .; \ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ + VMLINUX_SYMBOL(__start_rodata) = .; \ *(.rodata) *(.rodata.*) \ *(__vermagic) /* Kernel version magic */ \ } \ @@ -124,8 +124,8 @@ VMLINUX_SYMBOL(__start___param) = .; \ *(__param) \ VMLINUX_SYMBOL(__stop___param) = .; \ + VMLINUX_SYMBOL(__end_rodata) = .; \ } \ - __end_rodata = .; \ . = ALIGN(4096); #define SECURITY_INIT \ _ - 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/