[PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Aaron Merey]

If an auto-load script cannot be found and objfile is a separate
debuginfo whose filename does not match the name found in the parent
file's .gnu_debuglink section, then repeat the search using the
parent's filename where the last component is replaced with the
.gnu_debuglink name.

For example if the parent's filename is "/usr/lib/libxyz.so" and the
name in its .gnu_debuglink section is "libxyz.so.debug", then
if no auto-load script is otherwise found the search will be
repeated with the filename "/usr/lib/libxyz.so.debug".

This helps gdb locate auto-load scripts when debuginfo files do not have
the expected filename, such as when they are aquired from debuginfod.
---
 gdb/auto-load.c | 62 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 50 insertions(+), 12 deletions(-)

diff --git a/gdb/auto-load.c b/gdb/auto-load.c
index 680b87936b1..4ecec20d9cc 100644
--- a/gdb/auto-load.c
+++ b/gdb/auto-load.c
@@ -51,6 +51,9 @@
    followed by the path of a python script to load.  */
 #define AUTO_SECTION_NAME ".debug_gdb_scripts"
 
+/* The section to look in for the name of a separate debug file.  */
+#define DEBUGLINK_SECTION_NAME ".gnu_debuglink"
+
 static void maybe_print_unsupported_script_warning
   (struct auto_load_pspace_info *, struct objfile *objfile,
    const struct extension_language_defn *language,
@@ -820,24 +823,59 @@ auto_load_objfile_script (struct objfile *objfile,
   gdb::unique_xmalloc_ptr<char> realname
     = gdb_realpath (objfile_name (objfile));
 
-  if (!auto_load_objfile_script_1 (objfile, realname.get (), language))
+  if (auto_load_objfile_script_1 (objfile, realname.get (), language))
+    return;
+
+  /* For Windows/DOS .exe executables, strip the .exe suffix, so that
+     FOO-gdb.gdb could be used for FOO.exe, and try again.  */
+
+  size_t len = strlen (realname.get ());
+  const size_t lexe = sizeof (".exe") - 1;
+
+  if (len > lexe && strcasecmp (realname.get () + len - lexe, ".exe") == 0)
     {
-      /* For Windows/DOS .exe executables, strip the .exe suffix, so that
-	 FOO-gdb.gdb could be used for FOO.exe, and try again.  */
+      len -= lexe;
+      realname.get ()[len] = '\0';
+
+      auto_load_debug_printf
+	("auto-load: Stripped .exe suffix, retrying with \"%s\".",
+	 realname.get ());
+
+      auto_load_objfile_script_1 (objfile, realname.get (), language);
+      return;
+    }
 
-      size_t len = strlen (realname.get ());
-      const size_t lexe = sizeof (".exe") - 1;
+  /* If OBJFILE is a separate debug file and its name does not match
+     the name given in the parent's .gnu_debuglink section, try to
+     find the auto-load script using the parent's path and the
+     debuglink name.  */
+
+  struct objfile *parent = objfile->separate_debug_objfile_backlink;
+  if (parent != nullptr)
+    {
+      unsigned long crc32;
+      char *debuglink = bfd_get_debug_link_info (parent->obfd, &crc32);
 
-      if (len > lexe && strcasecmp (realname.get () + len - lexe, ".exe") == 0)
+      if (debuglink != nullptr
+	  && strcmp (debuglink, basename (realname.get ())) != 0)
 	{
-	  len -= lexe;
-	  realname.get ()[len] = '\0';
+	  /* Replace the last component of the parent's path with the
+	     debuglink name.  */
 
-	  auto_load_debug_printf
-	    ("auto-load: Stripped .exe suffix, retrying with \"%s\".",
-	     realname.get ());
+	  std::string p_realname = gdb_realpath (objfile_name (parent)).get ();
+	  size_t last = p_realname.find_last_of ('/');
 
-	  auto_load_objfile_script_1 (objfile, realname.get (), language);
+	  if (last != std::string::npos)
+	    {
+	      p_realname.replace (last + 1, std::string::npos, debuglink);
+
+	      auto_load_debug_printf
+		("Debug filename mismatch, retrying with \"%s\".",
+		 p_realname.c_str ());
+
+	      auto_load_objfile_script_1 (objfile,
+					  p_realname.c_str (), language);
+	    }
 	}
     }
 }
-- 
2.35.1

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Tom Tromey]

>>>>> "Aaron" == Aaron Merey via Gdb-patches <gdb-patches@sourceware.org> writes:

Aaron> For example if the parent's filename is "/usr/lib/libxyz.so" and the
Aaron> name in its .gnu_debuglink section is "libxyz.so.debug", then
Aaron> if no auto-load script is otherwise found the search will be
Aaron> repeated with the filename "/usr/lib/libxyz.so.debug".

Seems reasonable.

Aaron> +      char *debuglink = bfd_get_debug_link_info (parent->obfd, &crc32);

bfd_get_debug_link_info says it returns a malloc'd pointer, so I think
this is a memory leak.  Using gdb::unique_xmalloc_ptr<char> would solve
this.

Tom

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Aaron Merey]

Hi Tom,

On Fri, Mar 4, 2022 at 10:56 AM Tom Tromey <tom@tromey.com> wrote:
> Aaron> +      char *debuglink = bfd_get_debug_link_info (parent->obfd, &crc32);
>
> bfd_get_debug_link_info says it returns a malloc'd pointer, so I think
> this is a memory leak.  Using gdb::unique_xmalloc_ptr<char> would solve
> this.

Fixed, thanks.

Aaron

---
 gdb/auto-load.c | 64 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 52 insertions(+), 12 deletions(-)

diff --git a/gdb/auto-load.c b/gdb/auto-load.c
index 9a1ccec87ce..0acf2cee777 100644
--- a/gdb/auto-load.c
+++ b/gdb/auto-load.c
@@ -51,6 +51,9 @@
    followed by the path of a python script to load.  */
 #define AUTO_SECTION_NAME ".debug_gdb_scripts"
 
+/* The section to look in for the name of a separate debug file.  */
+#define DEBUGLINK_SECTION_NAME ".gnu_debuglink"
+
 static void maybe_print_unsupported_script_warning
   (struct auto_load_pspace_info *, struct objfile *objfile,
    const struct extension_language_defn *language,
@@ -823,24 +826,61 @@ auto_load_objfile_script (struct objfile *objfile,
   gdb::unique_xmalloc_ptr<char> realname
     = gdb_realpath (objfile_name (objfile));
 
-  if (!auto_load_objfile_script_1 (objfile, realname.get (), language))
+  if (auto_load_objfile_script_1 (objfile, realname.get (), language))
+    return;
+
+  /* For Windows/DOS .exe executables, strip the .exe suffix, so that
+     FOO-gdb.gdb could be used for FOO.exe, and try again.  */
+
+  size_t len = strlen (realname.get ());
+  const size_t lexe = sizeof (".exe") - 1;
+
+  if (len > lexe && strcasecmp (realname.get () + len - lexe, ".exe") == 0)
     {
-      /* For Windows/DOS .exe executables, strip the .exe suffix, so that
-	 FOO-gdb.gdb could be used for FOO.exe, and try again.  */
+      len -= lexe;
+      realname.get ()[len] = '\0';
+
+      auto_load_debug_printf
+	("auto-load: Stripped .exe suffix, retrying with \"%s\".",
+	 realname.get ());
+
+      auto_load_objfile_script_1 (objfile, realname.get (), language);
+      return;
+    }
 
-      size_t len = strlen (realname.get ());
-      const size_t lexe = sizeof (".exe") - 1;
+  /* If OBJFILE is a separate debug file and its name does not match
+     the name given in the parent's .gnu_debuglink section, try to
+     find the auto-load script using the parent's path and the
+     debuglink name.  */
+
+  struct objfile *parent = objfile->separate_debug_objfile_backlink;
+  if (parent != nullptr)
+    {
+      unsigned long crc32;
+      gdb::unique_xmalloc_ptr<char> debuglink
+	(bfd_get_debug_link_info (parent->obfd, &crc32));
 
-      if (len > lexe && strcasecmp (realname.get () + len - lexe, ".exe") == 0)
+      if (debuglink.get () != nullptr
+	  && strcmp (debuglink.get (), basename (realname.get ())) != 0)
 	{
-	  len -= lexe;
-	  realname.get ()[len] = '\0';
+	  /* Replace the last component of the parent's path with the
+	     debuglink name.  */
 
-	  auto_load_debug_printf
-	    ("auto-load: Stripped .exe suffix, retrying with \"%s\".",
-	     realname.get ());
+	  std::string p_realname = gdb_realpath (objfile_name (parent)).get ();
+	  size_t last = p_realname.find_last_of ('/');
 
-	  auto_load_objfile_script_1 (objfile, realname.get (), language);
+	  if (last != std::string::npos)
+	    {
+	      p_realname.replace (last + 1, std::string::npos,
+				  debuglink.get ());
+
+	      auto_load_debug_printf
+		("Debug filename mismatch, retrying with \"%s\".",
+		 p_realname.c_str ());
+
+	      auto_load_objfile_script_1 (objfile,
+					  p_realname.c_str (), language);
+	    }
 	}
     }
 }
-- 
2.35.1

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Tom Tromey]

>>>>> "Aaron" == Aaron Merey <amerey@redhat.com> writes:

Aaron> +	  && strcmp (debuglink.get (), basename (realname.get ())) != 0)

gdb normally uses lbasename and not plain basename.

This is ok with this fixed.

Tom

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Aaron Merey]

On Tue, Mar 8, 2022 at 7:26 PM Tom Tromey <tom@tromey.com> wrote:
>
> >>>>> "Aaron" == Aaron Merey <amerey@redhat.com> writes:
>
> Aaron> +          && strcmp (debuglink.get (), basename (realname.get ())) != 0)
>
> gdb normally uses lbasename and not plain basename.
>
> This is ok with this fixed.

Fixed. Pushed as commit 2e79bbf1e2.

Aaron

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Pedro Alves]

On 2022-03-08 22:41, Aaron Merey via Gdb-patches wrote:
> +      auto_load_debug_printf
> +	("auto-load: Stripped .exe suffix, retrying with \"%s\".",
> +	 realname.get ());
> +

With "auto-load:" in the fmt, doesn't gdb print "auto-load" twice?

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Aaron Merey]

Hi Pedro,

On Thu, Mar 10, 2022 at 1:26 PM Pedro Alves <pedro@palves.net> wrote:
>
> On 2022-03-08 22:41, Aaron Merey via Gdb-patches wrote:
> > +      auto_load_debug_printf
> > +     ("auto-load: Stripped .exe suffix, retrying with \"%s\".",
> > +      realname.get ());
> > +
>
> With "auto-load:" in the fmt, doesn't gdb print "auto-load" twice?

This was fixed in the second version of the patch I posted:

On Tue, Mar 8, 2022 at 5:41 PM Aaron Merey <amerey@redhat.com> wrote:
> +             auto_load_debug_printf
> +               ("Debug filename mismatch, retrying with \"%s\".",
> +                p_realname.c_str ());

The first version repeated "auto-load" because I based the message
on a pre-existing call to auto_load_debug_printf in auto_load_objfile_script
which contains a repeated "auto-load". That should be fixed and I will post
a patch for this.

Aaron

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Aaron Merey]

On Thu, Mar 10, 2022 at 3:16 PM Aaron Merey <amerey@redhat.com> wrote:
>
> Hi Pedro,
>
> On Thu, Mar 10, 2022 at 1:26 PM Pedro Alves <pedro@palves.net> wrote:
> >
> > On 2022-03-08 22:41, Aaron Merey via Gdb-patches wrote:
> > > +      auto_load_debug_printf
> > > +     ("auto-load: Stripped .exe suffix, retrying with \"%s\".",
> > > +      realname.get ());
> > > +
> >
> > With "auto-load:" in the fmt, doesn't gdb print "auto-load" twice?
>
> This was fixed in the second version of the patch I posted:
>
> On Tue, Mar 8, 2022 at 5:41 PM Aaron Merey <amerey@redhat.com> wrote:
> > +             auto_load_debug_printf
> > +               ("Debug filename mismatch, retrying with \"%s\".",
> > +                p_realname.c_str ());
>
> The first version repeated "auto-load" because I based the message
> on a pre-existing call to auto_load_debug_printf in auto_load_objfile_script
> which contains a repeated "auto-load". That should be fixed and I will post
> a patch for this.

Sorry Pedro, I mistook the function call you quoted for the call I added and
later fixed. The repeated auto-load you quoted was copied verbatim from a
pre-existing call to auto_load_debug_printf and was not fixed in the patch
that was merged. But like I said I will post a fix for this.

Aaron

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Tom Tromey]

Aaron> Sorry Pedro, I mistook the function call you quoted for the call I added and
Aaron> later fixed. The repeated auto-load you quoted was copied verbatim from a
Aaron> pre-existing call to auto_load_debug_printf and was not fixed in the patch
Aaron> that was merged. But like I said I will post a fix for this.

If it's just removing the prefix from the printf format, I think it
qualifies as obvious, just FYI.

Tom

Re: [PATCH] gdb: Try searching for auto-load script using .gnu_debuglink

[Pedro Alves]

On 2022-03-10 20:22, Aaron Merey wrote:
> On Thu, Mar 10, 2022 at 3:16 PM Aaron Merey <amerey@redhat.com> wrote:
>>
>> Hi Pedro,
>>
>> On Thu, Mar 10, 2022 at 1:26 PM Pedro Alves <pedro@palves.net> wrote:
>>>
>>> On 2022-03-08 22:41, Aaron Merey via Gdb-patches wrote:
>>>> +      auto_load_debug_printf
>>>> +     ("auto-load: Stripped .exe suffix, retrying with \"%s\".",
>>>> +      realname.get ());
>>>> +
>>>
>>> With "auto-load:" in the fmt, doesn't gdb print "auto-load" twice?
>>
>> This was fixed in the second version of the patch I posted:
>>
>> On Tue, Mar 8, 2022 at 5:41 PM Aaron Merey <amerey@redhat.com> wrote:
>>> +             auto_load_debug_printf
>>> +               ("Debug filename mismatch, retrying with \"%s\".",
>>> +                p_realname.c_str ());
>>
>> The first version repeated "auto-load" because I based the message
>> on a pre-existing call to auto_load_debug_printf in auto_load_objfile_script
>> which contains a repeated "auto-load". That should be fixed and I will post
>> a patch for this.
> 
> Sorry Pedro, I mistook the function call you quoted for the call I added and
> later fixed. The repeated auto-load you quoted was copied verbatim from a
> pre-existing call to auto_load_debug_printf and was not fixed in the patch
> that was merged. But like I said I will post a fix for this.

Thanks Aaron.