Re: Buildbot failure in Wildebeest Builder on whole buildset

[Mark Wielaard <mark@klomp.org>]

[-- Attachment #1: Type: text/plain, Size: 771 bytes --]

Hi,

On Wed, Oct 14, 2020 at 12:20:39AM +0200, Mark Wielaard wrote:
> So that is obviously my last commit. Sorry. All three buildbot workers
> fail on the same testcase pr25109.sh which is no-multifile-prop. That
> testcase has an empty debug_line and no decl/call_files. It still
> generates a .debug_line entry (and because no files have been seen, it
> produces a DWARF5 line table, which might be a bug in itself). I don't
> yet understand why this fails on ppc64, ppc64le and arm64 only and not
> on any other arch. Still investigating.

That was fun. It was a buffer overflow causing some on stack variables
to change values, but for some reason only on ppc64, ppc64 and
arm64. But it should have caused issues on all arches.

Pushed to attached fix.

Cheers,

Mark

[-- Attachment #2: 0001-Fix-buffer-overflow-in-write_multifile_line.patch --]
[-- Type: text/x-diff, Size: 1224 bytes --]

From babfff7baedefd5830340e2ad583b7732a895c49 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mark@klomp.org>
Date: Wed, 14 Oct 2020 12:30:27 +0200
Subject: [PATCH] Fix buffer overflow in write_multifile_line.

When writing out a "header only" .debug_line we use a small static
buffer on the stack. Make sure this buffer is large enough to contain
a DWARF5 empty line table header.

ChangeLog:

	* dwz.c (write_multi_line): Extend buf to 45 chars. Add assert
	to check buf is large enough.
---
 dwz.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/dwz.c b/dwz.c
index 1e6ec26..f8f2910 100644
--- a/dwz.c
+++ b/dwz.c
@@ -14304,7 +14304,7 @@ write_multifile_line (void)
   struct line_entry **filearr = NULL;
   struct line_stats line_stats;
   unsigned int *diridx = NULL, *dirarr = NULL;
-  unsigned char buf[17];
+  unsigned char buf[45]; /* Max header_len, see below.  */
   int ret = 0;
 
   line_stats.has_time = line_stats.has_size = false;
@@ -14430,7 +14430,10 @@ write_multifile_line (void)
 	}
 
       if (len == header_len)
-	line = buf;
+	{
+	  line = buf;
+	  assert (sizeof (buf) >= header_len);
+	}
       else
 	line = (unsigned char *) obstack_alloc (&ob, len);
     }
-- 
2.20.1