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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2017-02-03 09:54:06 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-03 08:28:25 -0800
commit71810db27c1c853b335675bee335d893bc3d324b (patch)
tree3816b3bfcf749dbdfa38ae289297209d8655fb36 /include/linux/module.h
parent56067812d5b0e737ac2063e94a50f76b810d6ca3 (diff)
downloadlinux-stericsson-71810db27c1c853b335675bee335d893bc3d324b.tar.gz
modversions: treat symbol CRCs as 32 bit quantities
The modversion symbol CRCs are emitted as ELF symbols, which allows us to easily populate the kcrctab sections by relying on the linker to associate each kcrctab slot with the correct value. This has a couple of downsides: - Given that the CRCs are treated as memory addresses, we waste 4 bytes for each CRC on 64 bit architectures, - On architectures that support runtime relocation, a R_<arch>_RELATIVE relocation entry is emitted for each CRC value, which identifies it as a quantity that requires fixing up based on the actual runtime load offset of the kernel. This results in corrupted CRCs unless we explicitly undo the fixup (and this is currently being handled in the core module code) - Such runtime relocation entries take up 24 bytes of __init space each, resulting in a x8 overhead in [uncompressed] kernel size for CRCs. Switching to explicit 32 bit values on 64 bit architectures fixes most of these issues, given that 32 bit values are not treated as quantities that require fixing up based on the actual runtime load offset. Note that on some ELF64 architectures [such as PPC64], these 32-bit values are still emitted as [absolute] runtime relocatable quantities, even if the value resolves to a build time constant. Since relative relocations are always resolved at build time, this patch enables MODULE_REL_CRCS on powerpc when CONFIG_RELOCATABLE=y, which turns the absolute CRC references into relative references into .rodata where the actual CRC value is stored. So redefine all CRC fields and variables as u32, and redefine the __CRC_SYMBOL() macro for 64 bit builds to emit the CRC reference using inline assembler (which is necessary since 64-bit C code cannot use 32-bit types to hold memory addresses, even if they are ultimately resolved using values that do not exceed 0xffffffff). To avoid potential problems with legacy 32-bit architectures using legacy toolchains, the equivalent C definition of the kcrctab entry is retained for 32-bit architectures. Note that this mostly reverts commit d4703aefdbc8 ("module: handle ppc64 relocating kcrctabs when CONFIG_RELOCATABLE=y") Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/module.h')
-rw-r--r--include/linux/module.h14
1 files changed, 7 insertions, 7 deletions
diff --git a/include/linux/module.h b/include/linux/module.h
index 7c84273d60b9..cc7cba219b20 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -346,7 +346,7 @@ struct module {
/* Exported symbols */
const struct kernel_symbol *syms;
- const unsigned long *crcs;
+ const s32 *crcs;
unsigned int num_syms;
/* Kernel parameters. */
@@ -359,18 +359,18 @@ struct module {
/* GPL-only exported symbols. */
unsigned int num_gpl_syms;
const struct kernel_symbol *gpl_syms;
- const unsigned long *gpl_crcs;
+ const s32 *gpl_crcs;
#ifdef CONFIG_UNUSED_SYMBOLS
/* unused exported symbols. */
const struct kernel_symbol *unused_syms;
- const unsigned long *unused_crcs;
+ const s32 *unused_crcs;
unsigned int num_unused_syms;
/* GPL-only, unused exported symbols. */
unsigned int num_unused_gpl_syms;
const struct kernel_symbol *unused_gpl_syms;
- const unsigned long *unused_gpl_crcs;
+ const s32 *unused_gpl_crcs;
#endif
#ifdef CONFIG_MODULE_SIG
@@ -382,7 +382,7 @@ struct module {
/* symbols that will be GPL-only in the near future. */
const struct kernel_symbol *gpl_future_syms;
- const unsigned long *gpl_future_crcs;
+ const s32 *gpl_future_crcs;
unsigned int num_gpl_future_syms;
/* Exception table */
@@ -523,7 +523,7 @@ struct module *find_module(const char *name);
struct symsearch {
const struct kernel_symbol *start, *stop;
- const unsigned long *crcs;
+ const s32 *crcs;
enum {
NOT_GPL_ONLY,
GPL_ONLY,
@@ -539,7 +539,7 @@ struct symsearch {
*/
const struct kernel_symbol *find_symbol(const char *name,
struct module **owner,
- const unsigned long **crc,
+ const s32 **crc,
bool gplok,
bool warn);