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From: Tom de Vries <>
Subject: [PATCH] Fix .debug_line reference above end of section
Date: Tue, 2 Mar 2021 14:57:14 +0100	[thread overview]
Message-ID: <20210302135713.GA22526@delia> (raw)


Consider the file test-import-repeatedly from PR26738, combined with a trivial
$ cp test-import-repeatedly 1
$ gcc -m32 -g ~/hello.c
$ cp a.out 2

When doing multifile optimization, we run into:
$ dwz -m 3 2 1
dwz: 3: .debug_line reference above end of section

Using --devel-save-temps and src/contrib/ we get the
unoptimized multifile, and find there a CU:
  Compilation Unit @ offset 0x371:
   Length:        0x6d (32-bit)
   Version:       4
   Abbrev Offset: 0x14d
   Pointer Size:  4
 <0><37c>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <37d>   DW_AT_stmt_list   : 0xda
    <381>   DW_AT_language    : 0       (Unknown: 0)
    <382>   DW_AT_comp_dir    : ./build-3.8
which refers to a .debug_line offset 0xda, but the debug_line section only
contains an entry at offset 0x0.

This can be explained as follows.  The DIEs written into the CU do not
contain a single DW_AT_decl_file.  Consequently, htab_line will be NULL once
we get here in write_multifile:
             || (line_htab != NULL && write_multifile_line ()))
and no .debug_line contribution will be added.  However, the CU DIE
referencing the .debug_line contribution is written regardless.

We could fix this by not writing the DW_AT_stmt_list for the CU DIE in this
case, but that would require changing the order in which abbreviations are

Instead, fix this conservatively, by removing "line_htab != NULL &&", such we
get a minimal .debug_line contribution.

Any comments?

- Tom

Fix .debug_line reference above end of section

2021-03-02  Tom de Vries  <>

	PR dwz/26738
	* dwz.c (write_multifile): Also call write_multifile_line when
	line_htab == NULL.

 dwz.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dwz.c b/dwz.c
index af1c5af..5effbc1 100644
--- a/dwz.c
+++ b/dwz.c
@@ -15150,7 +15150,7 @@ write_multifile (DSO *dso)
 		     != (ssize_t) debug_sections[DEBUG_MACRO].new_size)
 	      || (strp_htab != NULL && write_multifile_strp ())
-	      || (line_htab != NULL && write_multifile_line ()))
+	      || write_multifile_line ())
 	      error (0, 0, "Error writing multi-file temporary files");
 	      ret = 1;

             reply	other threads:[~2021-03-02 13:57 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-02 13:57 Tom de Vries [this message]
2021-03-04  0:33 ` Mark Wielaard
2021-03-04  8:33   ` Tom de Vries
2021-03-05  0:32     ` Mark Wielaard

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