module: handle ppc64 relocating kcrctabs when CONFIG_RELOCATABLE=y

powerpc applies relocations to the kcrctab.  They're absolute symbols,
but it's not completely unreasonable: other archs may too, but the
relocation is often 0.

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>
Tested-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
index 0845488..0192a4e 100644 (file)
--- 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
index 27735a7..dcd01c8 100644 (file)
--- 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
index 12afc5a..a65dc78 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -880,11 +880,23 @@ static int try_to_force_load(struct module *mod, const char *reason)
 }
 
 #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;
@@ -905,10 +917,10 @@ static int check_version(Elf_Shdr *sechdrs,
                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;
        }
 
@@ -931,7 +943,8 @@ static inline int check_modstruct_version(Elf_Shdr *sechdrs,
        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. */
@@ -949,7 +962,8 @@ static inline 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)
 {
        return 1;
 }
@@ -984,8 +998,8 @@ static const struct kernel_symbol *resolve_symbol(Elf_Shdr *sechdrs,
        /* 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;