The patch titled
Subject: kallsyms: don't overload absolute symbol type for percpu symbols
has been added to the -mm tree. Its filename is
kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols.patch
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From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Subject: kallsyms: don't overload absolute symbol type for percpu symbols
Commit c6bda7c988a5 ("kallsyms: fix percpu vars on x86-64 with
relocation") overloaded the 'A' (absolute) symbol type to signify that a
symbol is not subject to dynamic relocation. However, the original A type
does not imply that at all, and depending on the version of the toolchain,
many A type symbols are emitted that are in fact relative to the kernel
text, i.e., if the kernel is relocated at runtime, these symbols should be
updated as well.
For instance, on sparc32, the following symbols are emitted as absolute
(kindly provided by Guenter Roeck):
f035a420 A _etext
f03d9000 A _sdata
f03de8c4 A jiffies
f03f8860 A _edata
f03fc000 A __init_begin
f041bdc8 A __init_text_end
f0423000 A __bss_start
f0423000 A __init_end
f044457d A __bss_stop
f044457d A _end
On x86_64, similar behavior can be observed:
ffffffff81a00000 A __end_rodata_hpage_align
ffffffff81b19000 A __vvar_page
ffffffff81d3d000 A _end
Even if only a couple of them pass the symbol range check that results in
them to be taken into account for the final kallsyms symbol table, it is
obvious that 'A' does not mean the symbol does not need to be updated at
relocation time, and overloading its meaning to signify that is perhaps
not a good idea.
So instead, add a new percpu_absolute member to struct sym_entry, and when
--absolute-percpu is in effect, use it to record symbols whose addresses
should be emitted as final values rather than values that still require
relocation at runtime. That way, we can drop the check against the 'A'
type.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> # powerpc
Cc: Kees Cook <keescook@xxxxxxxxxxxx> # x86_64
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
scripts/kallsyms.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff -puN scripts/kallsyms.c~kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols scripts/kallsyms.c
--- a/scripts/kallsyms.c~kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols
+++ a/scripts/kallsyms.c
@@ -34,6 +34,7 @@ struct sym_entry {
unsigned int len;
unsigned int start_pos;
unsigned char *sym;
+ unsigned int percpu_absolute;
};
struct addr_range {
@@ -171,6 +172,8 @@ static int read_symbol(FILE *in, struct
strcpy((char *)s->sym + 1, str);
s->sym[0] = stype;
+ s->percpu_absolute = 0;
+
/* Record if we've found __per_cpu_start/end. */
check_symbol_range(sym, s->addr, &percpu_range, 1);
@@ -325,7 +328,7 @@ static int expand_symbol(unsigned char *
static int symbol_absolute(struct sym_entry *s)
{
- return toupper(s->sym[0]) == 'A';
+ return s->percpu_absolute;
}
static void write_src(void)
@@ -681,8 +684,15 @@ static void make_percpus_absolute(void)
unsigned int i;
for (i = 0; i < table_cnt; i++)
- if (symbol_in_range(&table[i], &percpu_range, 1))
+ if (symbol_in_range(&table[i], &percpu_range, 1)) {
+ /*
+ * Keep the 'A' override for percpu symbols to
+ * ensure consistent behavior compared to older
+ * versions of this tool.
+ */
table[i].sym[0] = 'A';
+ table[i].percpu_absolute = 1;
+ }
}
int main(int argc, char **argv)
_
Patches currently in -mm which might be from ard.biesheuvel@xxxxxxxxxx are
x86-kallsyms-disable-absolute-percpu-symbols-on-smp.patch
kallsyms-dont-overload-absolute-symbol-type-for-percpu-symbols.patch
kallsyms-add-support-for-relative-offsets-in-kallsyms-address-table.patch
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