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Re: [PATCH 1/2] Look for separate debug files in debug directories under a sysroot.


On 2019-01-22 20:03, John Baldwin wrote:
When an object file is present in a system root, GDB currently looks
for separate debug files under the global debugfile directories.  For
example, if the sysroot is set to "/myroot" and hte global debugfile
directory is set to "/usr/lib/debug", GDB will look for a separate
debug file for "/myroot/lib/libc.so.7" in the following paths:

  /myroot/lib/libc.so.7.debug
  /myroot/lib/.debug/libc.so.7.debug
  /usr/lib/debug//myroot/lib/libc.so.7.debug
  /usr/lib/debug/lib/libc.so.7.debug

However, some system roots include a full system installation
including a nested global debugfile directory under the sysroot.  This
patch adds an additional check to support such systems.  In the
example above the additional path searched is:

  /myroot/usr/lib/debug/lib/libc.so.7.debug

To try to preserve existing behavior as much as possible, this new
path is searched last for each global debugfile directory.

I played with this a bit using a Raspbian sysroot. I think the behavior you propose makes sense, perhaps more than the current behavior (I would be curious to see a real-word case for that one). But anyway, keeping the old behavior and adding a new one is fine. It's rather cheap to check many possible locations, and since there's a crc check, there's very little chance of loading a wrong separate debug file.

As discussed on IRC, we should probably add the same behavior for build-id-based separate debug files.

diff --git a/gdb/symfile.c b/gdb/symfile.c
index 7f800add8c..c6d2c7c537 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1465,6 +1465,25 @@ find_separate_debug_file (const char *dir,
 	  if (separate_debug_file_exists (debugfile, crc32, objfile))
 	    return debugfile;
 	}
+
+      /* If the file is in the sysroot, try using its base path in the
+	 sysroot's global debugfile directory.  */
+      if (canon_dir != NULL
+	  && filename_ncmp (canon_dir, gdb_sysroot,
+			    strlen (gdb_sysroot)) == 0
+	  && IS_DIR_SEPARATOR (canon_dir[strlen (gdb_sysroot)]))
+	{

Is there any reason to duplicate the if above? It looks to be the same as the previous check, so the new code could go in the existing if.

+	  debugfile = target_prefix ? "target:" : "";
+	  debugfile += gdb_sysroot;
+	  debugfile += debugdir.get ();
+	  debugfile += (canon_dir + strlen (gdb_sysroot));
+	  debugfile += "/";
+	  debugfile += debuglink;
+
+	  if (separate_debug_file_exists (debugfile, crc32, objfile))
+	    return debugfile;
+	}
+

Simon


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