Subject: Re: [PATCH] Correct printk %pF to work on all architectures

From: James Bottomley <[email-masked]>
Date: Wed, 03 Sep 2008 20:43:36 -0500

On Wed, 2008-09-03 at 17:01 -0700, Linus Torvalds wrote:
> 
> On Wed, 3 Sep 2008, James Bottomley wrote:
> > 
> > Oh ... because Arjan has a patch to export
> > dereference_function_descriptor.  I suppose I could make him do the
> > heavy lifting, but it seemed sensible to make it easy for him (and me)
> > by putting it in a header.
> > 
> > http://marc.info/?l=linux-kernel&m=121976793429869
> 
> Ahh.
> 
> NOW it all starts to make sense.
> 
> Or perhaps not sense, but I at least understand why people want to move it 
> around. The kernel.h location kind of goes together with that 
> core_kernel_text() thing, although it seems to be more of a "random 
> collection of routines" thing than anything else (but hey, that's the very 
> definition of "kernel.h" for you).
> 
> The module.h location still seems to be more of a "oh, both 
> kernel/extable.c and lib/vsprintf.c already included <linux/module.h>" and 
> it's a bit sad, since it really has nothing at all to do with modules.
> 
> Grr. It does seem like we don't have any kind of "abi" header file. 
> <linux/kernel.h> and <asm/processor.h> has various random things.
> 
> So yea, there doesn't seem to be any _obvious_ place that makes sense.
> 
> 		Linus
> 
> Not-very-strong-opinion: How about <asm/sections.h>? That does seem to be 
> where we already hide things like "in_kernel_text()" at least on powerpc. 
> In fact, since we already always have a generic version, the patch would 
> actually be something like
> 
>  - in <asm-generic/sections.h>, just do
> 
> 	#define dereference_function_descriptor(p) (p)
> 
>  - in architectures that want to override it
> 
> 	#undef dereference_function_descriptor
> 
>    followed by 
> 
> 	static inline void *dereference_function_descriptor(..) ..
> 	or
> 	#define dereference_function_descriptor my_fn_dereference
> 
>    since they all include the generic one as a base
> 
> Hmm? I do admit that "<asm/sections.h>" doesn't really strike me as a very 
> natural name for this, but kernel/extable.c does already include it for 
> other reasons, and it's at least no worse than module.h.

Well, good as any other I suppose.  So this is what you want?

James

---

It was introduced by 

commit 0fe1ef24f7bd0020f29ffe287dfdb9ead33ca0b2
Author: Linus Torvalds <[email-masked]>
Date:   Sun Jul 6 16:43:12 2008 -0700

    vsprintf: add support for '%pS' and '%pF' pointer formats

However, the current way its coded doesn't work on parisc64.  For two
reasons:  1) parisc isn't in the #ifdef and 2) parisc has a different
format for function descriptors

Make dereference_function_descriptor() more accommodating by allowing
architecture overrides.  I put the three overrides (for parisc64, ppc64
and ia64) in arch/kernel/module.c because that's where the kernel
internal linker which knows how to deal with function descriptors sits.

Signed-off-by: James Bottomley <[email-masked]>
---
 arch/ia64/include/asm/sections.h    |    3 +++
 arch/ia64/kernel/module.c           |   12 ++++++++++++
 arch/parisc/kernel/module.c         |   14 ++++++++++++++
 arch/powerpc/include/asm/sections.h |    3 +++
 arch/powerpc/kernel/module_64.c     |   13 ++++++++++++-
 include/asm-generic/sections.h      |    6 ++++++
 include/asm-parisc/sections.h       |    5 +++++
 lib/vsprintf.c                      |   11 +----------
 8 files changed, 56 insertions(+), 11 deletions(-)

diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
index 7286e4a..a7acad2 100644
--- a/arch/ia64/include/asm/sections.h
+++ b/arch/ia64/include/asm/sections.h
@@ -21,5 +21,8 @@ extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_b
 extern char __start_unwind[], __end_unwind[];
 extern char __start_ivt_text[], __end_ivt_text[];
 
+#undef dereference_function_descriptor
+void *dereference_function_descriptor(void *);
+
 #endif /* _ASM_IA64_SECTIONS_H */
 
diff --git a/arch/ia64/kernel/module.c b/arch/ia64/kernel/module.c
index 29aad34..545626f 100644
--- a/arch/ia64/kernel/module.c
+++ b/arch/ia64/kernel/module.c
@@ -31,9 +31,11 @@
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
 #include <linux/string.h>
+#include <linux/uaccess.h>
 #include <linux/vmalloc.h>
 
 #include <asm/patch.h>
+#include <asm/sections.h>
 #include <asm/unaligned.h>
 
 #define ARCH_MODULE_DEBUG 0
@@ -941,3 +943,13 @@ module_arch_cleanup (struct module *mod)
 	if (mod->arch.core_unw_table)
 		unw_remove_unwind_table(mod->arch.core_unw_table);
 }
+
+void *dereference_function_descriptor(void *ptr)
+{
+	struct fdesc *desc = ptr;
+	void *p;
+
+	if (!probe_kernel_address(&desc->ip, p))
+		ptr = p;
+	return ptr;
+}
diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index fdacdd4..44138c3 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -47,7 +47,9 @@
 #include <linux/string.h>
 #include <linux/kernel.h>
 #include <linux/bug.h>
+#include <linux/uaccess.h>
 
+#include <asm/sections.h>
 #include <asm/unwind.h>
 
 #if 0
@@ -860,3 +862,15 @@ void module_arch_cleanup(struct module *mod)
 	deregister_unwind_table(mod);
 	module_bug_cleanup(mod);
 }
+
+#ifdef CONFIG_64BIT
+void *dereference_function_descriptor(void *ptr)
+{
+	Elf64_Fdesc *desc = ptr;
+	void *p;
+
+	if (!probe_kernel_address(&desc->addr, p))
+		ptr = p;
+	return ptr;
+}
+#endif
diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index 916018e..7710e9e 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -16,6 +16,9 @@ static inline int in_kernel_text(unsigned long addr)
 	return 0;
 }
 
+#undef dereference_function_descriptor
+void *dereference_function_descriptor(void *);
+
 #endif
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index ee6a298..ad79de2 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -21,8 +21,9 @@
 #include <linux/err.h>
 #include <linux/vmalloc.h>
 #include <linux/bug.h>
+#include <linux/uaccess.h>
 #include <asm/module.h>
-#include <asm/uaccess.h>
+#include <asm/sections.h>
 #include <asm/firmware.h>
 #include <asm/code-patching.h>
 #include <linux/sort.h>
@@ -451,3 +452,13 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
 
 	return 0;
 }
+
+void *dereference_function_descriptor(void *ptr)
+{
+	struct ppc64_opd_entry *desc = ptr;
+	void *p;
+
+	if (!probe_kernel_address(&desc->funcaddr, p))
+		ptr = p;
+	return ptr;
+}
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 8feeae1..79a7ff9 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -14,4 +14,10 @@ extern char __kprobes_text_start[], __kprobes_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
 
+/* function descriptor handling (if any).  Override
+ * in asm/sections.h */
+#ifndef dereference_function_descriptor
+#define dereference_function_descriptor(p) (p)
+#endif
+
 #endif /* _ASM_GENERIC_SECTIONS_H_ */
diff --git a/include/asm-parisc/sections.h b/include/asm-parisc/sections.h
index fdd43ec..9d13c35 100644
--- a/include/asm-parisc/sections.h
+++ b/include/asm-parisc/sections.h
@@ -4,4 +4,9 @@
 /* nothing to see, move along */
 #include <asm-generic/sections.h>
 
+#ifdef CONFIG_64BIT
+#undef dereference_function_descriptor
+void *dereference_function_descriptor(void *);
+#endif
+
 #endif
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d8d1d11..c399bc1 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -27,6 +27,7 @@
 
 #include <asm/page.h>		/* for PAGE_SIZE */
 #include <asm/div64.h>
+#include <asm/sections.h>	/* for dereference_function_descriptor() */
 
 /* Works only for digits and letters, but small and fast */
 #define TOLOWER(x) ((x) | 0x20)
@@ -513,16 +514,6 @@ static char *string(char *buf, char *end, char *s, int field_width, int precisio
 	return buf;
 }
 
-static inline void *dereference_function_descriptor(void *ptr)
-{
-#if defined(CONFIG_IA64) || defined(CONFIG_PPC64)
-	void *p;
-	if (!probe_kernel_address(ptr, p))
-		ptr = p;
-#endif
-	return ptr;
-}
-
 static char *symbol_string(char *buf, char *end, void *ptr, int field_width, int precision, int flags)
 {
 	unsigned long value = (unsigned long) ptr;
-- 
1.5.6.5