Re: [PATCH][gdb] Mention CU offset for <artifical> if verbose

[Tom de Vries <tdevries@suse.de>]

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On 08-02-2020 16:48, Simon Marchi wrote:
> On 2020-02-08 4:16 a.m., Tom de Vries wrote:
>> On 07-02-2020 15:45, Christian Biesinger wrote:
>>> On Fri, Feb 7, 2020 at 6:34 AM Tom de Vries <tdevries@suse.de> wrote:
>>>
>>>
>>>> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
>>>> index dafe01d94a..28ade424fd 100644
>>>> --- a/gdb/dwarf2read.c
>>>> +++ b/gdb/dwarf2read.c
>>>> @@ -8020,6 +8020,20 @@ create_partial_symtab (struct dwarf2_per_cu_data *per_cu, const char *name)
>>>>    struct objfile *objfile = per_cu->dwarf2_per_objfile->objfile;
>>>>    dwarf2_psymtab *pst;
>>>>
>>>> +  const char *artificial = "<artificial>";
>>>
>>> This may not matter but I'd use static const char artificial[] = "..."
>>>
>>
>> Done.
>>
>>>> +  if (strcmp (name, artificial) == 0)
>>>> +    {
>>>> +      sect_offset cu_offset = per_cu->sect_off;
>>>> +      const char *cu_offset_str = sect_offset_str (cu_offset);
>>>> +      const char *sep = "@";
>>>> +      char *new_name = (char *) xmalloc (strlen (artificial) + strlen (sep)
>>>> +                                        + strlen (cu_offset_str) + 1);
>>>> +      strcpy (new_name, artificial);
>>>> +      strcat (new_name, sep);
>>>> +      strcat (new_name, cu_offset_str);
>>>
>>> Use concat() instead of malloc/strcpy/strcat?
>>>
>>
>> Done.
>>
>> Updated patch re-tested and attached.
> 
> Should the string allocated with concat be freed?

Indeed.

I've done that now by using gdb::unique_xmalloc_ptr<char>. [ FWIW,
there's some code in create_type_unit_group that does something similar,
but there we use std::string and string_printf. ]

Also, I realized that the code was too deep in the call stack, and I've
brought it one level up, to process_psymtab_comp_unit_reader, to make
sure it doesn't trigger for f.i. create_type_unit_group.

Thanks,
- Tom

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[gdb] Mention CU offset for <artifical> if verbose

Say we're debugging a test-case with CUs with name "<artificial>", meaning
not originating from a single file compilation, and use the verbose setting:
...
$ gdb -iex "set verbose on" -batch cc1
Reading symbols from cc1...
Reading in symbols for <artificial>... \
  and /tmp/trunk/gcc/attribs.c... \
  ...
  and /tmp/trunk/gcc/tree-ssa-reassoc.c... \
  done.
...

From the "/tmp/trunk/gcc/attribs.c" message, it's clear which CU is loaded.  But
that's not the case for the "<artificial>" message.

The message uses the filename field of struct partial_symtab, which is
documented like this:
...
  /* Name of the source file which this partial_symtab defines,
     or if the psymtab is anonymous then a descriptive name for
     debugging purposes, or "".  It must not be NULL.  */
...

So, fix this by setting the filename field to a more descriptive name than
"<artificial>", by appending the CU offset.

This way, we print instead:
...
$ gdb -iex "set verbose on" -batch cc1
Reading symbols from cc1...
Reading in symbols for <artificial>@0x41146d9 \
  and /tmp/trunk/gcc/attribs.c... \
  ... \
  and /tmp/trunk/gcc/tree-ssa-reassoc.c... \
  done.
...

Build and reg-tested on x86_64-linux.

gdb/ChangeLog:

2020-02-07  Tom de Vries  <tdevries@suse.de>

	* dwarf2read.c (process_psymtab_comp_unit_reader): Append CU offset to
	filename if it matches "<artificial>".

---
 gdb/dwarf2read.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index dafe01d94a..bd53dcc711 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -8059,9 +8059,17 @@ process_psymtab_comp_unit_reader (const struct die_reader_specs *reader,
   prepare_one_comp_unit (cu, comp_unit_die, pretend_language);
 
   /* Allocate a new partial symbol table structure.  */
+  gdb::unique_xmalloc_ptr<char> debug_filename;
+  static const char artificial[] = "<artificial>";
   filename = dwarf2_string_attr (comp_unit_die, DW_AT_name, cu);
   if (filename == NULL)
     filename = "";
+  else if (strcmp (filename, artificial) == 0)
+    {
+      debug_filename.reset (concat (artificial, "@",
+				    sect_offset_str (per_cu->sect_off), NULL));
+      filename = debug_filename.get ();
+    }
 
   pst = create_partial_symtab (per_cu, filename);