Commit 0fe1ef24 authored by Linus Torvalds's avatar Linus Torvalds

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

They print out a pointer in symbolic format, if possible (ie using
symbolic KALLSYMS information).  The '%pS' format is for regular direct
pointers (which can point to data or code and that you find on the stack
during backtraces etc), while '%pF' is for C function pointer types.

On most architectures, the two mean exactly the same thing, but some
architectures use an indirect pointer for C function pointers, where the
function pointer points to a function descriptor (which in turn contains
the actual pointer to the code).  The '%pF' code automatically does the
appropriate function descriptor dereference on such architectures.
Signed-off-by: default avatarLinus Torvalds <>
parent 4d8a743c
......@@ -22,6 +22,8 @@
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/kernel.h>
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <asm/page.h> /* for PAGE_SIZE */
#include <asm/div64.h>
......@@ -511,15 +513,52 @@ 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;
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;
char sym[KSYM_SYMBOL_LEN];
sprint_symbol(sym, value);
return string(buf, end, sym, field_width, precision, flags);
field_width = 2*sizeof(void *);
return number(buf, end, value, 16, field_width, precision, flags);
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
* specifiers.
* Right now don't actually handle any such, but we will..
* Right now we just handle 'F' (for symbolic Function descriptor pointers)
* and 'S' (for Symbolic direct pointers), but this can easily be
* extended in the future (network address types etc).
* The difference between 'S' and 'F' is that on ia64 and ppc64 function
* pointers are really function descriptors, which contain a pointer the
* real address.
static char *pointer(const char *fmt, char *buf, char *end, void *ptr, int field_width, int precision, int flags)
switch (*fmt) {
case 'F':
ptr = dereference_function_descriptor(ptr);
/* Fallthrough */
case 'S':
return symbol_string(buf, end, ptr, field_width, precision, flags);
flags |= SMALL;
if (field_width == -1) {
field_width = 2*sizeof(void *);
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