linux-kernel - [RFC 22/31] objtool: Make find_symbol

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Message-ID: <aec794961ec4bea48d47b4ff8da33072c3eba31f.1725334260.git.jpoimboe@kernel.org>
Date: Mon,  2 Sep 2024 21:00:05 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: live-patching@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Miroslav Benes <mbenes@...e.cz>,
	Petr Mladek <pmladek@...e.com>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Song Liu <song@...nel.org>
Subject: [RFC 22/31] objtool: Make find_symbol_containing() less arbitrary

In the rare case of overlapping symbols, find_symbol_containing() just
returns the first one it finds.  Make it less arbitrary by returning the
smallest symbol with size > 0.

Eventually we should consider making such overlapping symbols illegal.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/elf.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 7f89b0a99886..49528e7835aa 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -195,14 +195,29 @@ struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset)
 {
 	struct rb_root_cached *tree = (struct rb_root_cached *)&sec->symbol_tree;
-	struct symbol *iter;
+	struct symbol *sym = NULL, *tmp;
 
-	__sym_for_each(iter, tree, offset, offset) {
-		if (iter->type != STT_SECTION)
-			return iter;
+	__sym_for_each(tmp, tree, offset, offset) {
+		if (tmp->len) {
+			if (!sym) {
+				sym = tmp;
+				continue;
+			}
+
+			if (sym->offset != tmp->offset || sym->len != tmp->len) {
+				/*
+				 * In the rare case of overlapping symbols,
+				 * pick the smaller one.
+				 *
+				 * TODO: outlaw overlapping symbols
+				 */
+				if (tmp->len < sym->len)
+					sym = tmp;
+			}
+		}
 	}
 
-	return NULL;
+	return sym;
 }
 
 /*
-- 
2.45.2