+ kallsyms-should-prefer-non-weak-symbols.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     kallsyms should prefer non weak symbols
has been added to the -mm tree.  Its filename is
     kallsyms-should-prefer-non-weak-symbols.patch

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

------------------------------------------------------
Subject: kallsyms should prefer non weak symbols
From: Paulo Marques <pmarques@xxxxxxxxxxxx>

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.

Mathieu says:

  I created a module in LTTng that uses kallsyms to get the symbol
  corresponding to a specific system call address.  Unfortunately, all the
  unimplemented syscalls were all referring to the (same) weak symbol
  identifying an unrelated system call rather that sys_ni (or whatever
  non-weak symbol would be expected).  Kallsyms was dumbly returning the first
  symbol that matched.

  This patch makes sure kallsyms returns the non-weak symbol when there is
  one, which seems to be the expected result.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
Looks-great-to: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 scripts/kallsyms.c |   36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff -puN scripts/kallsyms.c~kallsyms-should-prefer-non-weak-symbols scripts/kallsyms.c
--- a/scripts/kallsyms.c~kallsyms-should-prefer-non-weak-symbols
+++ a/scripts/kallsyms.c
@@ -34,7 +34,7 @@
 
 struct sym_entry {
 	unsigned long long addr;
-	unsigned int len;
+	unsigned int len, start_pos;
 	unsigned char *sym;
 };
 
@@ -198,8 +198,10 @@ 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++;
+		}
 	}
 }
 
@@ -503,6 +505,35 @@ 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) {
@@ -523,6 +554,7 @@ int main(int argc, char **argv)
 		usage();
 
 	read_map(stdin);
+	sort_symbols();
 	optimize_token_table();
 	write_src();
 
_

Patches currently in -mm which might be from pmarques@xxxxxxxxxxxx are

kallsyms-should-prefer-non-weak-symbols.patch

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