[-mm PATCH] kallsyms should prefer non weak symbols

[Paulo Marques]

When resolving symbol names from addresses with aliased symbol names, 
kallsyms_lookup always returns the first symbol, even if it is a weak 
symbol.

This patch changes this by sorting the symbols with the weak symbols 
last before feeding them to the kernel. This way the kernel runtime 
isn't changed at all, only the kallsyms build system is changed.

Another side effect is that the symbols get sorted by address, too. So, 
even if future binutils version have some bug in "nm" that makes it fail 
to correctly sort symbols by address, the kernel won't be affected by this.


From: Paulo Marques <pmarques@xxxxxxxxxxxx>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>

--
Paulo Marques - www.grupopie.com

"There cannot be a crisis today; my schedule is already full."
--- ./scripts/kallsyms.c.orig	2007-10-30 18:51:28.000000000 +0000
+++ ./scripts/kallsyms.c	2007-10-30 19:07:58.000000000 +0000
@@ -34,7 +34,7 @@
 
 struct sym_entry {
 	unsigned long long addr;
-	unsigned int len;
+	unsigned int len, start_pos;
 	unsigned char *sym;
 };
 
@@ -202,8 +202,10 @@ static void read_map(FILE *in)
 				exit (1);
 			}
 		}
-		if (read_symbol(in, &table[table_cnt]) == 0)
+		if (read_symbol(in, &table[table_cnt]) == 0) {
+			table[table_cnt].start_pos = table_cnt;
 			table_cnt++;
+		}
 	}
 }
 
@@ -507,6 +509,35 @@ static void optimize_token_table(void)
 }
 
 
+static int compare_symbols(const void *a, const void *b)
+{
+	struct sym_entry *sa, *sb;
+	int wa, wb;
+
+	sa = (struct sym_entry *) a;
+	sb = (struct sym_entry *) b;
+
+	// sort by address first
+	if (sa->addr > sb->addr)
+		return 1;
+	if (sa->addr < sb->addr)
+		return -1;
+
+	// sort by "weakness" type
+	wa = (sa->sym[0] == 'w') || (sa->sym[0] == 'W');
+	wb = (sb->sym[0] == 'w') || (sb->sym[0] == 'W');
+	if (wa != wb)
+		return wa - wb;
+
+	// sort by initial order, so that other symbols are left undisturbed
+	return sa->start_pos - sb->start_pos;
+}
+
+static void sort_symbols(void)
+{
+	qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
+}
+
 int main(int argc, char **argv)
 {
 	if (argc >= 2) {
@@ -527,6 +558,7 @@ int main(int argc, char **argv)
 		usage();
 
 	read_map(stdin);
+	sort_symbols();
 	optimize_token_table();
 	write_src();