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SubjectRe: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on
Date
On Tue, 1 Dec 2009 04:46:00 am Neil Horman wrote:
> Paul, Ben, given that Rusty hasn't come back with any opinion on this patch, do you
> feel comfortable merging it via the ppc tree? Currently the earlyinit routine
> is only compiled in and used for your arch, so I think its fairly benign.

Sorry, I *did* track down the archives for linuxppc-dev, then find your post,
then read your patch. But I didn't actually reply.

Other than minor issues, there's one significant one: you shouldn't be trying
to change rodata. It might work on PPC today, but it's poor form at least.

How's this? Untested on ppc.

Other changes:
1) I also changed reloc_start to an array; this is a good idea for any
linker-defined symbols so the compiler can't make assumptions about size.
2) local.h? How about module.h?
3) I don't think the extra ". = 0" is necessary.
4) ARCH_USES_RELOC_ENTRIES isn't clear enough for me; I prefer
ARCH_RELOCATE_KCRCTAB.

module: handle ppc64 relocating kcrctabs when CONFIG_RELOCATABLE=y

http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-November/077972.html

Inspired-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
--- a/arch/powerpc/include/asm/module.h
+++ b/arch/powerpc/include/asm/module.h
@@ -87,5 +87,10 @@ struct exception_table_entry;
void sort_ex_table(struct exception_table_entry *start,
struct exception_table_entry *finish);

+#ifdef CONFIG_MODVERSIONS
+#define ARCH_RELOCATES_KCRCTAB
+
+extern const unsigned long reloc_start[];
+#endif
#endif /* __KERNEL__ */
#endif /* _ASM_POWERPC_MODULE_H */
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -38,6 +38,9 @@ jiffies = jiffies_64 + 4;
#endif
SECTIONS
{
+ . = 0;
+ reloc_start = .;
+
. = KERNELBASE;

/*
diff --git a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1030,11 +1030,23 @@ static int try_to_force_load(struct modu
}

#ifdef CONFIG_MODVERSIONS
+/* If the arch applies (non-zero) relocations to kernel kcrctab, unapply it. */
+static unsigned long maybe_relocated(unsigned long crc,
+ const struct module *crc_owner)
+{
+#ifdef ARCH_RELOCATES_KCRCTAB
+ if (crc_owner == NULL)
+ return crc - (unsigned long)reloc_start;
+#endif
+ return crc;
+}
+
static int check_version(Elf_Shdr *sechdrs,
unsigned int versindex,
const char *symname,
struct module *mod,
- const unsigned long *crc)
+ const unsigned long *crc,
+ const struct module *crc_owner)
{
unsigned int i, num_versions;
struct modversion_info *versions;
@@ -1055,10 +1067,10 @@ static int check_version(Elf_Shdr *sechd
if (strcmp(versions[i].name, symname) != 0)
continue;

- if (versions[i].crc == *crc)
+ if (versions[i].crc == maybe_relocated(*crc, crc_owner))
return 1;
DEBUGP("Found checksum %lX vs module %lX\n",
- *crc, versions[i].crc);
+ maybe_relocated(*crc, crc_owner), versions[i].crc);
goto bad_version;
}

@@ -1081,7 +1093,8 @@ static inline int check_modstruct_versio
if (!find_symbol(MODULE_SYMBOL_PREFIX "module_layout", NULL,
&crc, true, false))
BUG();
- return check_version(sechdrs, versindex, "module_layout", mod, crc);
+ return check_version(sechdrs, versindex, "module_layout", mod, crc,
+ NULL);
}

/* First part is kernel version, which we ignore if module has crcs. */
@@ -1099,7 +1112,8 @@ static inline int check_version(Elf_Shdr
unsigned int versindex,
const char *symname,
struct module *mod,
- const unsigned long *crc)
+ const unsigned long *crc,
+ const struct module *crc_owner)
{
return 1;
}
@@ -1134,8 +1148,8 @@ static const struct kernel_symbol *resol
/* use_module can fail due to OOM,
or module initialization or unloading */
if (sym) {
- if (!check_version(sechdrs, versindex, name, mod, crc) ||
- !use_module(mod, owner))
+ if (!check_version(sechdrs, versindex, name, mod, crc, owner)
+ || !use_module(mod, owner))
sym = NULL;
}
return sym;


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