Please suggest if there is a better way to handle this issue.
Thanks
Vivek
o Relocation patches for i386, moved the symbols in vmlinux.lds.S inside
sections so that these symbols become section relative and are no more
absolute. If these symbols become absolute, its bad as they are not
relocated if kernel is not loaded at the address it has been compiled
for.
o Ironically, just moving the symbols inside the section does not
gurantee that symbols inside will not become absolute. Looks like,
ld does some optimization, and if section size is zero, it gets
rid of the section and makes any defined symbol as absolute.
o This leads to a failure while second kernel is booting.
arch/i386/alternative.c frees any pages present between __smp_alt_begin
and __smp_alt_end. In my case size of section .smp_altinstructions is
zero and symbol __smpt_alt_begin becomes absolute and is not relocated
and system crashes while it is trying to free the memory starting
from __smp_alt_begin.
o One of the possible solutions is that force the section size to be
non zero to make sure these symbols don't become absolute. This
patch implements that. Ideally I should change include/asm-generic/vmlinux.lds
too, but I have not changed it right now as it will impact all the
arches and unnecessarily create 4byte sections. (Sections which shouldn't
have been present at all.) Please suggest if there is a better way to
handle the issue.
o This patch also move _end_rodata, symbol inside the section to force
it to become non-absolute symbols.
Signed-off-by: Vivek Goyal <[EMAIL PROTECTED]>
---
arch/i386/kernel/vmlinux.lds.S | 15 +++++++++++++++
include/asm-generic/vmlinux.lds.h | 2 +-
2 files changed, 16 insertions(+), 1 deletion(-)
diff -puN arch/i386/kernel/vmlinux.lds.S~i386-reloc-non-zero-size-section
arch/i386/kernel/vmlinux.lds.S
---
linux-2.6.17.i386/arch/i386/kernel/vmlinux.lds.S~i386-reloc-non-zero-size-section
2006-09-15 06:07:55.000000000 -0400
+++ linux-2.6.17.i386-root/arch/i386/kernel/vmlinux.lds.S 2006-09-15
06:14:41.000000000 -0400
@@ -48,6 +48,7 @@ SECTIONS
__start___ex_table = .;
*(__ex_table)
__stop___ex_table = .;
+ LONG(0)
}
RODATA
@@ -57,6 +58,7 @@ SECTIONS
__tracedata_start = .;
*(.tracedata)
__tracedata_end = .;
+ LONG(0)
}
/* writeable */
@@ -71,6 +73,7 @@ SECTIONS
*(.data.nosave)
. = ALIGN(4096);
__nosave_end = .;
+ LONG(0)
}
. = ALIGN(4096);
@@ -88,6 +91,7 @@ SECTIONS
.data.read_mostly : AT(ADDR(.data.read_mostly) - LOAD_OFFSET) {
*(.data.read_mostly)
_edata = .; /* End of data section */
+ LONG(0)
}
#ifdef CONFIG_STACK_UNWIND
@@ -96,6 +100,7 @@ SECTIONS
__start_unwind = .;
*(.eh_frame)
__end_unwind = .;
+ LONG(0)
}
#endif
@@ -111,17 +116,20 @@ SECTIONS
__smp_alt_instructions = .;
*(.smp_altinstructions)
__smp_alt_instructions_end = .;
+ LONG(0)
}
. = ALIGN(4);
.smp_locks : AT(ADDR(.smp_locks) - LOAD_OFFSET) {
__smp_locks = .;
*(.smp_locks)
__smp_locks_end = .;
+ LONG(0)
}
.smp_altinstr_replacement : AT(ADDR(.smp_altinstr_replacement) -
LOAD_OFFSET) {
*(.smp_altinstr_replacement)
. = ALIGN(4096);
__smp_alt_end = .;
+ LONG(0)
}
/* will be freed after init */
@@ -131,6 +139,7 @@ SECTIONS
_sinittext = .;
*(.init.text)
_einittext = .;
+ LONG(0)
}
.init.data : AT(ADDR(.init.data) - LOAD_OFFSET) { *(.init.data) }
. = ALIGN(16);
@@ -138,6 +147,7 @@ SECTIONS
__setup_start = .;
*(.init.setup)
__setup_end = .;
+ LONG(0)
}
.initcall.init : AT(ADDR(.initcall.init) - LOAD_OFFSET) {
__initcall_start = .;
@@ -149,11 +159,13 @@ SECTIONS
*(.initcall6.init)
*(.initcall7.init)
__initcall_end = .;
+ LONG(0)
}
.con_initcall.init : AT(ADDR(.con_initcall.init) - LOAD_OFFSET) {
__con_initcall_start = .;
*(.con_initcall.init)
__con_initcall_end = .;
+ LONG(0)
}
SECURITY_INIT
. = ALIGN(4);
@@ -161,6 +173,7 @@ SECTIONS
__alt_instructions = .;
*(.altinstructions)
__alt_instructions_end = .;
+ LONG(0)
}
.altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) {
*(.altinstr_replacement)
@@ -174,12 +187,14 @@ SECTIONS
__initramfs_start = .;
*(.init.ramfs)
__initramfs_end = .;
+ LONG(0)
}
. = ALIGN(L1_CACHE_BYTES);
.data.percpu : AT(ADDR(.data.percpu) - LOAD_OFFSET) {
__per_cpu_start = .;
*(.data.percpu)
__per_cpu_end = .;
+ LONG(0)
}
. = ALIGN(4096);
/* freed after init ends here */
diff -puN include/asm-generic/vmlinux.lds.h~i386-reloc-non-zero-size-section
include/asm-generic/vmlinux.lds.h
---
linux-2.6.17.i386/include/asm-generic/vmlinux.lds.h~i386-reloc-non-zero-size-section
2006-09-15 06:23:20.000000000 -0400
+++ linux-2.6.17.i386-root/include/asm-generic/vmlinux.lds.h 2006-09-15
06:24:40.000000000 -0400
@@ -117,8 +117,8 @@
/* Kernel symbol table: strings */ \
__ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) {
\
*(__ksymtab_strings) \
- } \
__end_rodata = .; \
+ } \
. = ALIGN(4096); \
\
/* Built-in module parameters. */ \
_
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