The patch titled
i386: Distinguish absolute symbols
has been added to the -mm tree. Its filename is
i386-distinguish-absolute-symbols.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: i386: Distinguish absolute symbols
From: Vivek Goyal <vgoyal@xxxxxxxxxx>
Eric Biederman implemented the relocatable kernel support for x86 and x86_64
and posted the patches for comments almost two months back.
http://marc.theaimsgroup.com/?l=linux-kernel&m=115443019026302&w=2
We have been testing the patches in RHEL kernels since then and things are
looking up. I think this is the time that patches can be included in -mm and
get more testing done and get rest of the issues sorted out.
Eric is currently held up with other things, so I have taken his patches and
forward ported to 2.6.18-git19. Did some minor cleanups and fixed a couple of
bugs as faced in our testing. I have also accomodated the review comments
received last time.
Currently this patch series is only for i386. I will be posting the patches
for x86_64 later.
Following is a brief account of changes I have done since last time.
o Forward ported the patches to 2.6.18-git19
o Replaced CONFIG_PHYSICAL_START with CONFIG_PHYSICAL_ALIGN
o Added a patch to prevent section relative symbols becoming absolute
for sections with zero size.
o Dropped support for serial output debugging in decompressor code for
the time being as per the discussion last time.
o Added symbol _text to few architectures so that compilation does not break
o Fix a typo in config option (CONFIG_RELOCTABLE). It was causing wrong pice
of code to be executed and second kernel was stomping over first kernel's
data.
o Modified __pa_symbol() definition as per Andi's comment.
o Put --emit-relocs undef #ifdef, so that relocation sections are not
retained of CONFIG_RELOCATABLE is not set.
o Made symbol _end_rodata also section relative.
o Align .data section to 4K address otherwise data segment is loaded at
a non-4K aligned boundary and kexec-tools do the check.
Following is the text from Eric's last post to refresh memory that why do we
need a relocatable kernel.
The problem:
We can't always run the kernel at 1MB or 2MB, and so people who need different
addresses must build multiple kernels. The bzImage format can't even
represent loading a kernel at other than it's default address. With kexec on
panic now starting to be used by distros having a kernel not running at the
default load address is starting to become common.
The goal of this patch series is to build kernels that are relocatable at run
time, and to extend the bzImage format to make it capable of expressing a
relocatable kernel.
In extending the bzImage format I am replacing the existing unused bootsector
with an ELF header. To express what is going on the ELF header will have type
ET_DYN. Just like the kernel loading an ET_DYN executable bootloaders are not
expected to process relocations. But the executable may be shifted in the
address space so long as it's alignment requirements are met.
The i386 kernel is built to process relocations generated with --emit-relocs
(after vmlinux.lds.S) has been fixed up to sort out static and dynamic
relocations.
This patch:
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 <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
arch/i386/kernel/vmlinux.lds.S | 107 +++++++++++++++-------------
include/asm-generic/vmlinux.lds.h | 4 -
2 files changed, 60 insertions(+), 51 deletions(-)
diff -puN arch/i386/kernel/vmlinux.lds.S~i386-distinguish-absolute-symbols arch/i386/kernel/vmlinux.lds.S
--- a/arch/i386/kernel/vmlinux.lds.S~i386-distinguish-absolute-symbols
+++ a/arch/i386/kernel/vmlinux.lds.S
@@ -24,33 +24,36 @@ 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 */
+ } :text = 0x9090
_etext = .; /* End of text section */
. = 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 = .;
+ }
_sdata = .; /* End of text section */
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 */
@@ -59,10 +62,12 @@ 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) {
@@ -76,8 +81,10 @@ 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);
@@ -95,39 +102,41 @@ 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)
@@ -135,20 +144,20 @@ 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)
}
@@ -157,32 +166,32 @@ 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-distinguish-absolute-symbols include/asm-generic/vmlinux.lds.h
--- a/include/asm-generic/vmlinux.lds.h~i386-distinguish-absolute-symbols
+++ a/include/asm-generic/vmlinux.lds.h
@@ -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 \
_
Patches currently in -mm which might be from vgoyal@xxxxxxxxxx are
origin.patch
i386-distinguish-absolute-symbols.patch
i386-align-data-section-to-4k-boundary.patch
i386-force-section-size-to-be-non-zero-to-prevent-a-symbol-becoming-absolute.patch
i386-define-__pa_symbol.patch
i386-setupc-reserve-kernel-memory-starting-from-_text.patch
i386-config_physical_start-cleanup.patch
make-linux-elfh-safe-to-be-included-in-assembly-files.patch
elf-add-elfosabi_standalone-to-elfh.patch
kallsyms-generate-relocatable-symbols.patch
i386-relocatable-kernel-support.patch
i386-implement-config_physical_align.patch
i386-boot-add-an-elf-header-to-bzimage.patch
-
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