[RFC] kallsyms_lookup always requires buffers

[Franck Bui-Huu <vagabon.xyz@gmail.com>]

Hi,

Some uses of kallsyms_lookup() do not need to find out the name of
a symbol and its module's name it belongs. This is specially true
in arch specific code, which needs to unwind the stack to show the
back trace during opps (mips is an example). In this specific case,
we just need to retreive the function's size and the offset of the
active intruction inside it.

This simple patch adds a new entry "kallsyms_lookup_gently()". The
name actually sucks but I can't figure out a coherent name with the
rest of the file. If someone could give me a better idea...
This new entry does exactly the same as kallsyms_lookup() but does
not require any buffers to store any names. It returns 0 if it fails
otherwise 1.

Do you think this can be usefull ?

thanks
		Franck

-- >8 --

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 849043c..30f8d8d 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -12,6 +12,10 @@ #ifdef CONFIG_KALLSYMS
 /* Lookup the address for a symbol. Returns 0 if not found. */
 unsigned long kallsyms_lookup_name(const char *name);
 
+extern int kallsyms_lookup_gently(unsigned long addr,
+				  unsigned long *symbolsize,
+				  unsigned long *offset);
+
 /* Lookup an address.  modname is set to NULL if it's in the kernel. */
 const char *kallsyms_lookup(unsigned long addr,
 			    unsigned long *symbolsize,
@@ -28,6 +32,13 @@ static inline unsigned long kallsyms_loo
 	return 0;
 }
 
+static inline const int kallsyms_lookup_gently(unsigned long addr,
+					       unsigned long *symbolsize,
+					       unsigned long *offset)
+{
+	return 0;
+}
+
 static inline const char *kallsyms_lookup(unsigned long addr,
 					  unsigned long *symbolsize,
 					  unsigned long *offset,
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index ab16a5a..c398753 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -69,6 +69,15 @@ static inline int is_kernel(unsigned lon
 	return in_gate_area_no_task(addr);
 }
 
+static int is_kernel_addr(unsigned long addr)
+{
+	if (all_var)
+		return is_kernel(addr);
+
+	return is_kernel_text(addr) || is_kernel_inittext(addr) ||
+		is_kernel_extratext(addr);
+}
+
 /* expand a compressed symbol data into the resulting uncompressed string,
    given the offset to where the symbol is in the compressed stream */
 static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
@@ -156,6 +165,78 @@ unsigned long kallsyms_lookup_name(const
 }
 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
 
+static unsigned long get_symbol_pos(unsigned long addr,
+				    unsigned long *symbolsize,
+				    unsigned long *offset)
+{
+	unsigned long symbol_start = 0, symbol_end = 0;
+	unsigned long i, low, high, mid;
+
+	/* This kernel should never had been booted. */
+	BUG_ON(!kallsyms_addresses);
+
+	/* do a binary search on the sorted kallsyms_addresses array */
+	low = 0;
+	high = kallsyms_num_syms;
+
+	while (high - low > 1) {
+		mid = (low + high) / 2;
+		if (kallsyms_addresses[mid] <= addr)
+			low = mid;
+		else
+			high = mid;
+	}
+
+	/*
+	 * search for the first aliased symbol. Aliased
+	 * symbols are symbols with the same address
+	 */
+	while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low])
+		--low;
+
+	symbol_start = kallsyms_addresses[low];
+
+	/* Search for next non-aliased symbol */
+	for (i = low + 1; i < kallsyms_num_syms; i++) {
+		if (kallsyms_addresses[i] > symbol_start) {
+			symbol_end = kallsyms_addresses[i];
+			break;
+		}
+	}
+	
+	/* if we found no next symbol, we use the end of the section */
+	if (!symbol_end) {
+		if (is_kernel_inittext(addr))
+			symbol_end = (unsigned long)_einittext;
+		else if (all_var)
+			symbol_end = (unsigned long)_end;
+		else 
+			symbol_end = (unsigned long)_etext;
+	}
+
+	*symbolsize = symbol_end - symbol_start;
+	*offset = addr - symbol_start;
+
+	return low;
+}
+
+/*
+ * Lookup an address but don't bother to find any names.
+ */
+int kallsyms_lookup_gently(unsigned long addr, unsigned long *symbolsize,
+			   unsigned long *offset)
+{
+	int rv;
+
+	if (is_kernel_addr(addr))
+		rv = !!get_symbol_pos(addr, symbolsize, offset);
+	else
+		rv = !!module_address_lookup(addr, symbolsize, offset, NULL);
+
+	return rv;
+}
+EXPORT_SYMBOL_GPL(kallsyms_lookup_gently);
+
 /*
  * Lookup an address
  * - modname is set to NULL if it's in the kernel
@@ -168,57 +249,18 @@ const char *kallsyms_lookup(unsigned lon
 			    unsigned long *offset,
 			    char **modname, char *namebuf)
 {
-	unsigned long i, low, high, mid;
 	const char *msym;
 
-	/* This kernel should never had been booted. */
-	BUG_ON(!kallsyms_addresses);
-
 	namebuf[KSYM_NAME_LEN] = 0;
 	namebuf[0] = 0;
 
-	if ((all_var && is_kernel(addr)) ||
-	    (!all_var && (is_kernel_text(addr) || is_kernel_inittext(addr) ||
-				is_kernel_extratext(addr)))) {
-		unsigned long symbol_end = 0;
-
-		/* do a binary search on the sorted kallsyms_addresses array */
-		low = 0;
-		high = kallsyms_num_syms;
-
-		while (high-low > 1) {
-			mid = (low + high) / 2;
-			if (kallsyms_addresses[mid] <= addr) low = mid;
-			else high = mid;
-		}
-
-		/* search for the first aliased symbol. Aliased symbols are
-		   symbols with the same address */
-		while (low && kallsyms_addresses[low - 1] == kallsyms_addresses[low])
-			--low;
-
+	if (is_kernel_addr(addr)) {
+		unsigned long pos;
+		
+		pos = get_symbol_pos(addr, symbolsize, offset);
 		/* Grab name */
-		kallsyms_expand_symbol(get_symbol_offset(low), namebuf);
-
-		/* Search for next non-aliased symbol */
-		for (i = low + 1; i < kallsyms_num_syms; i++) {
-			if (kallsyms_addresses[i] > kallsyms_addresses[low]) {
-				symbol_end = kallsyms_addresses[i];
-				break;
-			}
-		}
-
-		/* if we found no next symbol, we use the end of the section */
-		if (!symbol_end) {
-			if (is_kernel_inittext(addr))
-				symbol_end = (unsigned long)_einittext;
-			else
-				symbol_end = all_var ? (unsigned long)_end : (unsigned long)_etext;
-		}
-
-		*symbolsize = symbol_end - kallsyms_addresses[low];
+		kallsyms_expand_symbol(get_symbol_offset(pos), namebuf);
 		*modname = NULL;
-		*offset = addr - kallsyms_addresses[low];
 		return namebuf;
 	}
 
diff --git a/kernel/module.c b/kernel/module.c
index 2a19cd4..0e3e6ab 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2012,7 +2012,8 @@ const char *module_address_lookup(unsign
 	list_for_each_entry(mod, &modules, list) {
 		if (within(addr, mod->module_init, mod->init_size)
 		    || within(addr, mod->module_core, mod->core_size)) {
-			*modname = mod->name;
+			if (modname)
+				*modname = mod->name;
 			return get_ksymbol(mod, addr, size, offset);
 		}
 	}