linux-kernel - [PATCH] tools/objtool: tolerate STT

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Message-Id: <20221220101323.3119939-1-npiggin@gmail.com>
Date:   Tue, 20 Dec 2022 20:13:23 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] tools/objtool: tolerate STT_NOTYPE symbols at end of section

Hand-written asm often contains non-function symbols in executable
sections. _end symbols for finding the size of instruction blocks
for runtime processing is one such usage.

optprobe_template_end is one example that causes the warning:

  objtool: optprobe_template_end(): can't find starting instruction

This is because the symbol happens to be at the end of the file (and
therefore end of a section in the object file).

So ignore end-of-section STT_NOTYPE symbols instead of bailing out
because an instruction can't be found. While we're here, add a more
descriptive warning for STT_FUNC symbols found at the end of a
section.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
 tools/objtool/check.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4350be739f4f..4b7c8b33069e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -427,6 +427,15 @@ static int decode_instructions(struct objtool_file *file)
 			if (func->type != STT_NOTYPE && func->type != STT_FUNC)
 				continue;
 
+			if (func->offset == sec->sh.sh_size) {
+				/* Heuristic: likely an "end" symbol */
+				if (func->type == STT_NOTYPE)
+					continue;
+				WARN("%s(): STT_FUNC at end of section",
+				     func->name);
+				return -1;
+			}
+
 			if (func->return_thunk || func->alias != func)
 				continue;
 
-- 
2.37.2