[PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

Hey there-
	Before anyone flames me for what a oddball solution this is, let me just
say I'm trying to get the ball rolling here.  I think there may be better
solutions that can be impemented in reloc_64.S, but I've yet to make any of the
ones I've tried work successfully.  I'm open to suggestions, but this solution
is the only one so far that I've been able to get to work. thanks :)


Adjust crcs in __kcrctab_* sections if relocs are used with CONFIG_RELOCATABLE

When CONFIG_MODVERSIONS and CONFIG_RELOCATABLE are enabled on powerpc platforms,
kdump has been failing in a rather odd way.  specifically modules will not
install.  This is because when validating the crcs of symbols that the module
needs, the crc of the module never matches the crc that is stored in the kernel.

The underlying cause of this is how CONFIG_MODVERSIONS is implemented, and how
CONFIG_RELOCATABLE are implemented.  with CONFIG_MODVERSIONS enabled, for every
exported symbol in the kernel we emit 2 symbols, __crc_#sym which is declared
extern and __kcrctab_##sym, which is placed in the __kcrctab section of the
binary.  The latter has its value set equal to the address of the former
(recalling it is declared extern).  After the object file is built, genksyms is
run on the processed source, and crcs are computed for each exported symbol.
genksyms then emits a linker script which defines each of the needed __crc_##sym
symbols, and sets their addresses euqal to their respective crcs.  This script
is then used in a secondary link to the previously build object file, so that
the crcs of the missing symbol can be validated on module insert.

The problem here is that because __kcrctab_sym is set equal to &__crc_##sym, a
relocation entry is emitted by the compiler for the __kcrctab__##sym.  Normally
this is not a problem, since relocation on other arches is done without the aid
of .rel.dyn sections.  PPC however uses these relocations when
CONFIG_RELOCATABLE is enabled.  nominally, since addressing starts at 0 for ppc,
its irrelevant, but if we start at a non-zero address (like we do when booting
via kexec from reserved crashkernel memory), the ppc boot code iterates over the
relocation entries, and winds up adding that relocation offset to all symbols,
including the symbols that are actually the aforementioned crc values in the
__kcrctab_* sections.  This effectively corrupts the crcs and prevents any
module loads from happening during a kdump.

My solution is to 'undo' these relocations prior to boot up.  If
ARCH_USES_RELOC_ENTRIES is defined, we add a symbol at address zero to the
linker script for that arch (I call it reloc_start, so that &reloc_start = 0).
This symbol will then indicate the relocation offset for any given boot.  We
also add an initcall to the module code that, during boot, scans the __kcrctab_*
sections and subtracts &reloc_start from every entry in those sections,
restoring the appropriate crc value.

I've verified that this allows kexec to work properly on ppc64 systems myself.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>


 arch/powerpc/include/asm/local.h  |    6 ++++++
 arch/powerpc/kernel/vmlinux.lds.S |    4 ++++
 kernel/module.c                   |   30 ++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
index 84b457a..9cc49e5 100644
--- a/arch/powerpc/include/asm/local.h
+++ b/arch/powerpc/include/asm/local.h
@@ -4,6 +4,12 @@
 #include <linux/percpu.h>
 #include <asm/atomic.h>
 
+#ifdef CONFIG_MODVERSIONS
+#define ARCH_USES_RELOC_ENTRIES
+
+extern unsigned long reloc_start;
+#endif
+
 typedef struct
 {
 	atomic_long_t a;
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 27735a7..2b9fb2e 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -38,6 +38,10 @@ jiffies = jiffies_64 + 4;
 #endif
 SECTIONS
 {
+	. = 0;
+	reloc_start = .;
+	. = 0;
+
 	. = KERNELBASE;
 
 /*
diff --git a/kernel/module.c b/kernel/module.c
index 8b7d880..87a4928 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -181,8 +181,11 @@ extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
 extern const struct kernel_symbol __start___ksymtab_gpl_future[];
 extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
 extern const unsigned long __start___kcrctab[];
+extern const unsigned long __stop___kcrctab[];
 extern const unsigned long __start___kcrctab_gpl[];
+extern const unsigned long __stop___kcrctab_gpl[];
 extern const unsigned long __start___kcrctab_gpl_future[];
+extern const unsigned long __stop___kcrctab_gpl_future[];
 #ifdef CONFIG_UNUSED_SYMBOLS
 extern const struct kernel_symbol __start___ksymtab_unused[];
 extern const struct kernel_symbol __stop___ksymtab_unused[];
@@ -3144,3 +3147,30 @@ int module_get_iter_tracepoints(struct tracepoint_iter *iter)
 	return found;
 }
 #endif
+
+#ifdef ARCH_USES_RELOC_ENTRIES
+static __init int adjust_kcrctab(void)
+{
+	int i;
+	int count;
+	unsigned long  *crc ;
+
+	count = __stop___kcrctab - __start___kcrctab;
+	crc = (unsigned long *)__start___kcrctab;
+	for (i = 0; i < count; i++) {
+		crc[i] -= (unsigned long)&reloc_start;
+	}
+	count = __stop___kcrctab_gpl - __start___kcrctab_gpl;
+	crc = (unsigned long *)__start___kcrctab_gpl;
+	for (i = 0; i < count; i++) {
+		crc[i] -= (unsigned long)&reloc_start;
+	}
+	count = __stop___kcrctab_gpl_future - __start___kcrctab_gpl_future;
+	crc = (unsigned long *)__start___kcrctab_gpl_future;
+	for (i = 0; i< count; i++) {
+                crc[i] -= (unsigned long)&reloc_start;
+	}
+	return 0;
+}
+early_initcall(adjust_kcrctab);
+#endif

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Paul Mackerras]

Neil Horman writes:

> 	Before anyone flames me for what a oddball solution this is, let me just
> say I'm trying to get the ball rolling here.  I think there may be better
> solutions that can be impemented in reloc_64.S, but I've yet to make any of the
> ones I've tried work successfully.  I'm open to suggestions, but this solution
> is the only one so far that I've been able to get to work. thanks :)

I had thought that the CRCs would be the only things with reloc
addends less than 4G, but it turns out that the toolchain folds
expressions like __pa(&sym) into just a load from a doubleword (in the
TOC) containing the physical address of sym.  That needs to be
relocated and its reloc addend will be less than 4GB.  Hence the
crashes early in boot that you were seeing with my proposed patch to
reloc_64.S.

Given that, your solution seems as reasonable as any.  Should this go
via the modules maintainer, Rusty Russell, perhaps?

In any case,

Acked-by: Paul Mackerras <paulus@samba.org>

> Adjust crcs in __kcrctab_* sections if relocs are used with CONFIG_RELOCATABLE
> 
> When CONFIG_MODVERSIONS and CONFIG_RELOCATABLE are enabled on powerpc platforms,
> kdump has been failing in a rather odd way.  specifically modules will not
> install.  This is because when validating the crcs of symbols that the module
> needs, the crc of the module never matches the crc that is stored in the kernel.
> 
> The underlying cause of this is how CONFIG_MODVERSIONS is implemented, and how
> CONFIG_RELOCATABLE are implemented.  with CONFIG_MODVERSIONS enabled, for every
> exported symbol in the kernel we emit 2 symbols, __crc_#sym which is declared
> extern and __kcrctab_##sym, which is placed in the __kcrctab section of the
> binary.  The latter has its value set equal to the address of the former
> (recalling it is declared extern).  After the object file is built, genksyms is
> run on the processed source, and crcs are computed for each exported symbol.
> genksyms then emits a linker script which defines each of the needed __crc_##sym
> symbols, and sets their addresses euqal to their respective crcs.  This script
> is then used in a secondary link to the previously build object file, so that
> the crcs of the missing symbol can be validated on module insert.
> 
> The problem here is that because __kcrctab_sym is set equal to &__crc_##sym, a
> relocation entry is emitted by the compiler for the __kcrctab__##sym.  Normally
> this is not a problem, since relocation on other arches is done without the aid
> of .rel.dyn sections.  PPC however uses these relocations when
> CONFIG_RELOCATABLE is enabled.  nominally, since addressing starts at 0 for ppc,
> its irrelevant, but if we start at a non-zero address (like we do when booting
> via kexec from reserved crashkernel memory), the ppc boot code iterates over the
> relocation entries, and winds up adding that relocation offset to all symbols,
> including the symbols that are actually the aforementioned crc values in the
> __kcrctab_* sections.  This effectively corrupts the crcs and prevents any
> module loads from happening during a kdump.
> 
> My solution is to 'undo' these relocations prior to boot up.  If
> ARCH_USES_RELOC_ENTRIES is defined, we add a symbol at address zero to the
> linker script for that arch (I call it reloc_start, so that &reloc_start = 0).
> This symbol will then indicate the relocation offset for any given boot.  We
> also add an initcall to the module code that, during boot, scans the __kcrctab_*
> sections and subtracts &reloc_start from every entry in those sections,
> restoring the appropriate crc value.
> 
> I've verified that this allows kexec to work properly on ppc64 systems myself.
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 
> 
>  arch/powerpc/include/asm/local.h  |    6 ++++++
>  arch/powerpc/kernel/vmlinux.lds.S |    4 ++++
>  kernel/module.c                   |   30 ++++++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> index 84b457a..9cc49e5 100644
> --- a/arch/powerpc/include/asm/local.h
> +++ b/arch/powerpc/include/asm/local.h
> @@ -4,6 +4,12 @@
>  #include <linux/percpu.h>
>  #include <asm/atomic.h>
>  
> +#ifdef CONFIG_MODVERSIONS
> +#define ARCH_USES_RELOC_ENTRIES
> +
> +extern unsigned long reloc_start;
> +#endif
> +
>  typedef struct
>  {
>  	atomic_long_t a;
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 27735a7..2b9fb2e 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -38,6 +38,10 @@ jiffies = jiffies_64 + 4;
>  #endif
>  SECTIONS
>  {
> +	. = 0;
> +	reloc_start = .;
> +	. = 0;
> +
>  	. = KERNELBASE;
>  
>  /*
> diff --git a/kernel/module.c b/kernel/module.c
> index 8b7d880..87a4928 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -181,8 +181,11 @@ extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
>  extern const struct kernel_symbol __start___ksymtab_gpl_future[];
>  extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
>  extern const unsigned long __start___kcrctab[];
> +extern const unsigned long __stop___kcrctab[];
>  extern const unsigned long __start___kcrctab_gpl[];
> +extern const unsigned long __stop___kcrctab_gpl[];
>  extern const unsigned long __start___kcrctab_gpl_future[];
> +extern const unsigned long __stop___kcrctab_gpl_future[];
>  #ifdef CONFIG_UNUSED_SYMBOLS
>  extern const struct kernel_symbol __start___ksymtab_unused[];
>  extern const struct kernel_symbol __stop___ksymtab_unused[];
> @@ -3144,3 +3147,30 @@ int module_get_iter_tracepoints(struct tracepoint_iter *iter)
>  	return found;
>  }
>  #endif
> +
> +#ifdef ARCH_USES_RELOC_ENTRIES
> +static __init int adjust_kcrctab(void)
> +{
> +	int i;
> +	int count;
> +	unsigned long  *crc ;
> +
> +	count = __stop___kcrctab - __start___kcrctab;
> +	crc = (unsigned long *)__start___kcrctab;
> +	for (i = 0; i < count; i++) {
> +		crc[i] -= (unsigned long)&reloc_start;
> +	}
> +	count = __stop___kcrctab_gpl - __start___kcrctab_gpl;
> +	crc = (unsigned long *)__start___kcrctab_gpl;
> +	for (i = 0; i < count; i++) {
> +		crc[i] -= (unsigned long)&reloc_start;
> +	}
> +	count = __stop___kcrctab_gpl_future - __start___kcrctab_gpl_future;
> +	crc = (unsigned long *)__start___kcrctab_gpl_future;
> +	for (i = 0; i< count; i++) {
> +                crc[i] -= (unsigned long)&reloc_start;
> +	}
> +	return 0;
> +}
> +early_initcall(adjust_kcrctab);
> +#endif

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

On Thu, Nov 19, 2009 at 02:52:16PM -0500, Neil Horman wrote:
> Hey there-
> 	Before anyone flames me for what a oddball solution this is, let me just
> say I'm trying to get the ball rolling here.  I think there may be better
> solutions that can be impemented in reloc_64.S, but I've yet to make any of the
> ones I've tried work successfully.  I'm open to suggestions, but this solution
> is the only one so far that I've been able to get to work. thanks :)
> 
> 
> Adjust crcs in __kcrctab_* sections if relocs are used with CONFIG_RELOCATABLE
> 
> When CONFIG_MODVERSIONS and CONFIG_RELOCATABLE are enabled on powerpc platforms,
> kdump has been failing in a rather odd way.  specifically modules will not
> install.  This is because when validating the crcs of symbols that the module
> needs, the crc of the module never matches the crc that is stored in the kernel.
> 
> The underlying cause of this is how CONFIG_MODVERSIONS is implemented, and how
> CONFIG_RELOCATABLE are implemented.  with CONFIG_MODVERSIONS enabled, for every
> exported symbol in the kernel we emit 2 symbols, __crc_#sym which is declared
> extern and __kcrctab_##sym, which is placed in the __kcrctab section of the
> binary.  The latter has its value set equal to the address of the former
> (recalling it is declared extern).  After the object file is built, genksyms is
> run on the processed source, and crcs are computed for each exported symbol.
> genksyms then emits a linker script which defines each of the needed __crc_##sym
> symbols, and sets their addresses euqal to their respective crcs.  This script
> is then used in a secondary link to the previously build object file, so that
> the crcs of the missing symbol can be validated on module insert.
> 
> The problem here is that because __kcrctab_sym is set equal to &__crc_##sym, a
> relocation entry is emitted by the compiler for the __kcrctab__##sym.  Normally
> this is not a problem, since relocation on other arches is done without the aid
> of .rel.dyn sections.  PPC however uses these relocations when
> CONFIG_RELOCATABLE is enabled.  nominally, since addressing starts at 0 for ppc,
> its irrelevant, but if we start at a non-zero address (like we do when booting
> via kexec from reserved crashkernel memory), the ppc boot code iterates over the
> relocation entries, and winds up adding that relocation offset to all symbols,
> including the symbols that are actually the aforementioned crc values in the
> __kcrctab_* sections.  This effectively corrupts the crcs and prevents any
> module loads from happening during a kdump.
> 
> My solution is to 'undo' these relocations prior to boot up.  If
> ARCH_USES_RELOC_ENTRIES is defined, we add a symbol at address zero to the
> linker script for that arch (I call it reloc_start, so that &reloc_start = 0).
> This symbol will then indicate the relocation offset for any given boot.  We
> also add an initcall to the module code that, during boot, scans the __kcrctab_*
> sections and subtracts &reloc_start from every entry in those sections,
> restoring the appropriate crc value.
> 
> I've verified that this allows kexec to work properly on ppc64 systems myself.
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 
Ping, any thoughts here?  As I've been mulling this over, I'm beginning to like
this solution better than a completely arch-specific section, as this approach
makes common the bits that any arch is going to need if they implement
CONFIG_RELOCATABLE with a .rel[a].* section set.  The alternative is of course
to simply skip the appropriate relocations, but thats something that every arch
will need to discover on their own.  This makes it a bit more clear whats
happening I think.

Regards
Neil

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

Neil Horman writes:

> 	Before anyone flames me for what a oddball solution this is, let me just
> say I'm trying to get the ball rolling here.  I think there may be better
> solutions that can be impemented in reloc_64.S, but I've yet to make any of
the
> ones I've tried work successfully.  I'm open to suggestions, but this solution
> is the only one so far that I've been able to get to work. thanks :)

I had thought that the CRCs would be the only things with reloc
addends less than 4G, but it turns out that the toolchain folds
expressions like __pa(&sym) into just a load from a doubleword (in the
TOC) containing the physical address of sym.  That needs to be
relocated and its reloc addend will be less than 4GB.  Hence the
crashes early in boot that you were seeing with my proposed patch to
reloc_64.S.

Given that, your solution seems as reasonable as any.  Should this go
via the modules maintainer, Rusty Russell, perhaps?

In any case,

Acked-by: Paul Mackerras <paulus at samba.org>


I'm not 100% sure, it does kind of split the middle in regards to what tree is
should come through.

Rusy, given the previous entries in this thread, do you have any thoughts on the
patch, or which tree it should go through?  I kind of think that the ppc tree is
just fine here since its currently the only user of this code, but I'll defer to
other opinions on the subject.

Thanks & Regards
Neil

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

On Thu, Nov 19, 2009 at 02:52:16PM -0500, Neil Horman wrote:
> Hey there-
> 	Before anyone flames me for what a oddball solution this is, let me just
> say I'm trying to get the ball rolling here.  I think there may be better
> solutions that can be impemented in reloc_64.S, but I've yet to make any of the
> ones I've tried work successfully.  I'm open to suggestions, but this solution
> is the only one so far that I've been able to get to work. thanks :)
> 
> 
> Adjust crcs in __kcrctab_* sections if relocs are used with CONFIG_RELOCATABLE
> 
> When CONFIG_MODVERSIONS and CONFIG_RELOCATABLE are enabled on powerpc platforms,
> kdump has been failing in a rather odd way.  specifically modules will not
> install.  This is because when validating the crcs of symbols that the module
> needs, the crc of the module never matches the crc that is stored in the kernel.
> 
> The underlying cause of this is how CONFIG_MODVERSIONS is implemented, and how
> CONFIG_RELOCATABLE are implemented.  with CONFIG_MODVERSIONS enabled, for every
> exported symbol in the kernel we emit 2 symbols, __crc_#sym which is declared
> extern and __kcrctab_##sym, which is placed in the __kcrctab section of the
> binary.  The latter has its value set equal to the address of the former
> (recalling it is declared extern).  After the object file is built, genksyms is
> run on the processed source, and crcs are computed for each exported symbol.
> genksyms then emits a linker script which defines each of the needed __crc_##sym
> symbols, and sets their addresses euqal to their respective crcs.  This script
> is then used in a secondary link to the previously build object file, so that
> the crcs of the missing symbol can be validated on module insert.
> 
> The problem here is that because __kcrctab_sym is set equal to &__crc_##sym, a
> relocation entry is emitted by the compiler for the __kcrctab__##sym.  Normally
> this is not a problem, since relocation on other arches is done without the aid
> of .rel.dyn sections.  PPC however uses these relocations when
> CONFIG_RELOCATABLE is enabled.  nominally, since addressing starts at 0 for ppc,
> its irrelevant, but if we start at a non-zero address (like we do when booting
> via kexec from reserved crashkernel memory), the ppc boot code iterates over the
> relocation entries, and winds up adding that relocation offset to all symbols,
> including the symbols that are actually the aforementioned crc values in the
> __kcrctab_* sections.  This effectively corrupts the crcs and prevents any
> module loads from happening during a kdump.
> 
> My solution is to 'undo' these relocations prior to boot up.  If
> ARCH_USES_RELOC_ENTRIES is defined, we add a symbol at address zero to the
> linker script for that arch (I call it reloc_start, so that &reloc_start = 0).
> This symbol will then indicate the relocation offset for any given boot.  We
> also add an initcall to the module code that, during boot, scans the __kcrctab_*
> sections and subtracts &reloc_start from every entry in those sections,
> restoring the appropriate crc value.
> 
> I've verified that this allows kexec to work properly on ppc64 systems myself.
> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 

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.

Regards
Neil

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Rusty Russell]

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;

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Rusty Russell]

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;

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

>> 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.
>
I'll try grab a ppc64 system and test this soon.

>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.
Ok, I'll certainly trust your linker skill over mine :)

>2) local.h?  How about module.h?
Seems good to me
>3) I don't think the extra ". = 0" is necessary.
Its not, I was just trying to be clear about where reloc_start was to be placed.

>4) ARCH_USES_RELOC_ENTRIES isn't clear enough for me; I prefer
>   ARCH_RELOCATE_KCRCTAB.
Sounds good to me.


I'll test this as soon as I'm able
Thanks!
Neil

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Neil Horman]

>>> 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.
>>
>I'll try grab a ppc64 system and test this soon.
>
>>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.
>Ok, I'll certainly trust your linker skill over mine :)
>
>>2) local.h?  How about module.h?
>Seems good to me
>>3) I don't think the extra ". = 0" is necessary.
>Its not, I was just trying to be clear about where reloc_start was to be placed.
>
>>4) ARCH_USES_RELOC_ENTRIES isn't clear enough for me; I prefer
>>   ARCH_RELOCATE_KCRCTAB.
>Sounds good to me.
>
>
>I'll test this as soon as I'm able
>Thanks!
>Neil
>

Just finished testing your patch Rusty, it all works quite well, Thanks!
Will this be going in via your tree, or the ppc tree?

Acked-by: Neil Horman <nhorman@tuxdriver.com>

Neil

Re: [PATCH] ppc64: re-enable kexec to allow module loads with CONFIG_MODVERSIONS and CONFIG_RELOCATABLE turned on

[Rusty Russell]

On Fri, 4 Dec 2009 01:34:17 am Neil Horman wrote:
> Just finished testing your patch Rusty, it all works quite well, Thanks!
> Will this be going in via your tree, or the ppc tree?

It's in my tree now.  Since I didn't really alter the ppc parts, I kept
Paul's ack attached too.

Thanks,
Rusty.