[RFC,v2,6/7] symbol lookup: use new kernel and module dereference functions

Commit Message

Sergey Senozhatsky Sept. 20, 2017, 4:29 p.m. UTC

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

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

This patch also removes dereference_function_descriptor() from
'%pF/%pf' vsprintf handler, because it has the same behavior with
'%pS/%ps' now.

Signed-off-by: Sergey Senozhatsky <[e-mail]>
---
 Documentation/printk-formats.txt | 15 +++++----------
 kernel/kallsyms.c                |  1 +
 kernel/module.c                  |  1 +
 lib/vsprintf.c                   |  5 +----
 4 files changed, 8 insertions(+), 14 deletions(-)

Comments

Sergey Senozhatsky Sept. 21, 2017, 9:38 a.m. UTC | #1

On (09/21/17 01:29), Sergey Senozhatsky wrote:
[..]
> +	%pS	versatile_init+0x0/0x110
> +	%ps	versatile_init
>  	%pF	versatile_init+0x0/0x110
>  	%pf	versatile_init
> -	%pS	versatile_init+0x0/0x110
>  	%pSR	versatile_init+0x9/0x110
>  		(with __builtin_extract_return_addr() translation)
> -	%ps	versatile_init
>  	%pB	prev_fn_of_versatile_init+0x88/0x88
>  
> -The ``F`` and ``f`` specifiers are for printing function pointers,
> -for example, f->func, &gettimeofday. They have the same result as
> -``S`` and ``s`` specifiers. But they do an extra conversion on
> -ia64, ppc64 and parisc64 architectures where the function pointers
> -are actually function descriptors.
> -
>  The ``S`` and ``s`` specifiers can be used for printing symbols
>  from direct addresses, for example, __builtin_return_address(0),
>  (void *)regs->ip. They result in the symbol name with (``S``) or
>  without (``s``) offsets. If KALLSYMS are disabled then the symbol
>  address is printed instead.
>  
> +Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
> +and thus deprecated.

JFI,

I have updated this part. it's probably too early to completely
wipe out pF/pf info.

the updated Doc goes like this:

+Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
+and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and
+parisc64 function pointers are indirect and, in fact, are function
+descriptors, which require additional dereferencing before we can lookup
+the symbol. As of now, ``S`` and ``s`` perform dereferencing on those
+platforms (when needed), so ``F`` and ``f`` exist for compatibility
+reasons only.

	-ss
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Patch

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 361789df51ec..b2afafc84638 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -50,26 +50,23 @@  Symbols/Function Pointers
 
 ::
 
+	%pS	versatile_init+0x0/0x110
+	%ps	versatile_init
 	%pF	versatile_init+0x0/0x110
 	%pf	versatile_init
-	%pS	versatile_init+0x0/0x110
 	%pSR	versatile_init+0x9/0x110
 		(with __builtin_extract_return_addr() translation)
-	%ps	versatile_init
 	%pB	prev_fn_of_versatile_init+0x88/0x88
 
-The ``F`` and ``f`` specifiers are for printing function pointers,
-for example, f->func, &gettimeofday. They have the same result as
-``S`` and ``s`` specifiers. But they do an extra conversion on
-ia64, ppc64 and parisc64 architectures where the function pointers
-are actually function descriptors.
-
 The ``S`` and ``s`` specifiers can be used for printing symbols
 from direct addresses, for example, __builtin_return_address(0),
 (void *)regs->ip. They result in the symbol name with (``S``) or
 without (``s``) offsets. If KALLSYMS are disabled then the symbol
 address is printed instead.
 
+Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
+and thus deprecated.
+
 The ``B`` specifier results in the symbol name with offsets and should be
 used when printing stack backtraces. The specifier takes into
 consideration the effect of compiler optimisations which may occur
@@ -77,8 +74,6 @@  when tail-call``s are used and marked with the noreturn GCC attribute.
 
 Examples::
 
-	printk("Going to call: %pF\n", gettimeofday);
-	printk("Going to call: %pF\n", p->func);
 	printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
 	printk("%s: called from %pS\n", __func__,
 				(void *)__builtin_return_address(0));
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 127e7cfafa55..e2fc09ea9509 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -322,6 +322,7 @@  const char *kallsyms_lookup(unsigned long addr,
 	if (is_ksym_addr(addr)) {
 		unsigned long pos;
 
+		addr = dereference_kernel_function_descriptor(addr);
 		pos = get_symbol_pos(addr, symbolsize, offset);
 		/* Grab name */
 		kallsyms_expand_symbol(get_symbol_offset(pos),
diff --git a/kernel/module.c b/kernel/module.c
index b792e814150a..63361de377ad 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3948,6 +3948,7 @@  const char *module_address_lookup(unsigned long addr,
 	preempt_disable();
 	mod = __module_address(addr);
 	if (mod) {
+		addr = dereference_module_function_descriptor(mod, addr);
 		if (modname)
 			*modname = mod->name;
 		ret = get_ksymbol(mod, addr, size, offset);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index bcd906a39010..bf04b4f5d8e7 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>
@@ -1721,10 +1720,8 @@  char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	}
 
 	switch (*fmt) {
-	case 'F':
+	case 'F': /* %pF and %pf are kept for compatibility reasons only */
 	case 'f':
-		ptr = (void *)dereference_function_descriptor((unsigned long)ptr);
-		/* Fallthrough */
 	case 'S':
 	case 's':
 	case 'B':