symbol lookup: introduce dereference_symbol_descriptor()

dereference_symbol_descriptor() invokes appropriate ARCH specific
function descriptor dereference callbacks:
- dereference_kernel_function_descriptor() if the pointer is a
  kernel symbol;

- dereference_module_function_descriptor() if the pointer is a
  module symbol.

This is the last step needed to make '%pS/%ps' smart enough to
handle function descriptor dereference on affected ARCHs and
to retire '%pF/%pf'.

To refresh it:
  Some architectures (ia64, ppc64, parisc64) use an indirect pointer
  for C function pointers - the function pointer points to a function
  descriptor and we need to dereference it to get the actual function
  pointer.

  Function descriptors live in .opd elf section and all affected
  ARCHs (ia64, ppc64, parisc64) handle it properly for kernel and
  modules. So we, technically, can decide if the dereference is
  needed by simply looking at the pointer: if it belongs to .opd
  section then we need to dereference it.

  The kernel and modules have their own .opd sections, obviously,
  that's why we need to split dereference_function_descriptor()
  and use separate kernel and module dereference arch callbacks.

Link: http://lkml.kernel.org/r/20171206043649.GB15885@jagdpanzerIV
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: James Bottomley <jejb@parisc-linux.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-ia64@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Tested-by: Tony Luck <tony.luck@intel.com> #ia64
Tested-by: Santosh Sivaraj <santosh@fossix.org> #powerpc
Tested-by: Helge Deller <deller@gmx.de> #parisc64
Signed-off-by: Petr Mladek <pmladek@suse.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 1746bae..16e2eef 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -40,7 +40,6 @@
 #include "../mm/internal.h"	/* For the trace_print_flags arrays */
 
 #include <asm/page.h>		/* for PAGE_SIZE */
-#include <asm/sections.h>	/* for dereference_function_descriptor() */
 #include <asm/byteorder.h>	/* cpu_to_le16 */
 
 #include <linux/string_helpers.h>
@@ -1723,10 +1722,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	switch (*fmt) {
 	case 'F':
 	case 'f':
-		ptr = dereference_function_descriptor(ptr);
-		/* Fallthrough */
 	case 'S':
 	case 's':
+		ptr = dereference_symbol_descriptor(ptr);
+		/* Fallthrough */
 	case 'B':
 		return symbol_string(buf, end, ptr, spec, fmt);
 	case 'R':