public inbox for dwz@sourceware.org
 help / color / mirror / Atom feed
From: Mark Wielaard <mark@klomp.org>
To: Tom de Vries <tdevries@suse.de>
Cc: dwz@sourceware.org, jakub@redhat.com
Subject: Re: [PATCH] Fix .debug_line reference above end of section
Date: Fri, 5 Mar 2021 01:32:56 +0100	[thread overview]
Message-ID: <20210305003256.GM3014@wildebeest.org> (raw)
In-Reply-To: <9bda5bfa-b2dc-84e5-df99-0c62929b934b@suse.de>

Hi Tom,

On Thu, Mar 04, 2021 at 09:33:43AM +0100, Tom de Vries wrote:
> On 3/4/21 1:33 AM, Mark Wielaard wrote:
> > I was unable to replicate this, so it is a little harder to comment in
> > this. I don't fully understand why this happens, is this because of
> > something in the input file or because we move all DIEs with file
> > attributes?
> > 
> 
> This is because all the DIEs from the input file that are written into
> the unoptimized multifile don't have any attributes referring to the
> file table.
> 
> > Would it be possible to attach the various temp files to the bug
> > report?
> > 
> 
> Done.

Thanks. It turns out I was confused because I was using eu-readelf and
that doesn't handle DWARF Units which contain zero DIEs. I'll write a
patch for elfutils.

> > This does look technically OK. write_multifile_line does handle line_htab == NULL
> > correctly and sets up multi_line_off which will be used to write the
> > DW_AT_stmt_list.
> > 
> > But if the CU doesn't have a DW_AT_stmt_list this will produce an
> > unnecessary line table (stub). 
> 
> Ack.  The fix is conservative.
> 
> > I cannot immediately see whether this
> > is an odd corner case that normally wouldn't happen in practice or if
> > that could happen more often.
> 
> I've seen this error before, so it's not completely cornercase.

I tried to come up with something different, but your fix is much
simpler. So please push what you have.

This is what I came up with, which makes sure there always is a
line_htab, even if it is empty. But even in write_unit_die we don't
yet know if there will be actual files. So we still end up writing the
DW_AT_stmt_list with the current multi_line_off, so we must produce a
debug_line entry anyway.

diff --git a/dwz.c b/dwz.c
index af1c5af..c493c1d 100644
--- a/dwz.c
+++ b/dwz.c
@@ -9929,6 +9929,16 @@ line_eq (const void *p, const void *q)
   return s1->file->time == s2->file->time && s1->file->size == s2->file->size;
 }
 
+static htab_t
+line_htab_create (void)
+{
+  htab_t htab = htab_try_create (50, line_hash, line_eq, NULL);
+  if (htab == NULL)
+    dwz_oom ();
+  max_line_id = 1;
+  return htab;
+}
+
 /* Map original file ID to new file ID.  */
 static unsigned int
 line_htab_lookup (dw_cu_ref cu, unsigned int id)
@@ -9947,12 +9957,7 @@ line_htab_lookup (dw_cu_ref cu, unsigned int id)
   if (le.file->dir)
     h = iterative_hash (le.file->dir, strlen (le.file->dir) + 1, h);
   if (line_htab == NULL)
-    {
-      line_htab = htab_try_create (50, line_hash, line_eq, NULL);
-      if (line_htab == NULL)
-	dwz_oom ();
-      max_line_id = 1;
-    }
+    line_htab = line_htab_create ();
   le.hash = h;
   slot = htab_find_slot_with_hash (line_htab, &le, h, INSERT);
   if (slot == NULL)
@@ -12222,7 +12227,11 @@ write_unit_die (unsigned char *ptr, dw_die_ref die, dw_die_ref origin)
 	    assert (p && (form == DW_FORM_sec_offset
 			  || form == DW_FORM_data4));
 	    if (wr_multifile)
-	      write_32 (ptr, multi_line_off);
+	      {
+		write_32 (ptr, multi_line_off);
+		if (line_htab == NULL)
+		  line_htab = line_htab_create ();
+	      }
 	    else if (op_multifile)
 	      write_32 (ptr, 0);
 	    else

Cheers,

Mark


      reply	other threads:[~2021-03-05  0:34 UTC|newest]

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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210305003256.GM3014@wildebeest.org \
    --to=mark@klomp.org \
    --cc=dwz@sourceware.org \
    --cc=jakub@redhat.com \
    --cc=tdevries@suse.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).