[PR22771] binutils/nm: nm does not display file/line information for inlined functions

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  • [PR22771] binutils/nm: nm does not display file/line information for inlined functions
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Commit Message

Carroll, Paul Feb. 5, 2018, 8:01 p.m.
The nm utility supports -l for using debug information to obtain file 
and line information for each symbol, if available.
We have a tool that consumes this information and displays it.
This identified a problem with the 'nm' utility.

When a source is compiled with -O2, functions can be inlined.  The 
compiler also produces an uninlined copy of the function, normally for 
linking to other object files.
In the case of DWARF2 debug information, the compiler generates debug 
information to describe a function.  If that function is inlined, the 
compiler then references that debug information from the inlined and 
uninlined copies of the routine through the use of the 
DW_AT_abstract_origin reference.
When nm is used on such a file, it is not able to find file and line 
information because that information is present in the common debug 
information and not at each actual implementation of the function.
The 'nm' utility only retrieves the name of the function from the 
abstract origin debug information and no more.

What I am proposing is to modify the find_abstract_instance_name() 
function (which I renamed to find_abstract_instance() ) to return the 
name of the function as well as any file and line information.  The 
routine is already parsing all of the debug information in the abstract 
instance, so it is easy to pick up the file and line information at that 
time. If, for some reason, the file and line information is not present, 
the routine behaves as before.

For example, if I have a simple test case:

int foo(int j)
{
         if (j < 15)
                 j += j << 2;
         else
                 j += j << 6;
         return j;
}

int main (int argc,char **argv)
{
         int i = argc;
         i += foo(i);
         return i;
}

If that test case is compiled with -O2 and then 'nm -l' reads that 
executable, it currently produces this symbol output (ignoring a lot of 
library symbols):

8048400 T foo
080482e0 T main /scratch/pcarroll/its254/test/mytest.c:12

If I modify 'nm' to return file and line information for abstract 
instances, it produces the following output:

08048400 T foo  /scratch/pcarroll/its254/test/mytest.c:1
080482e0 T main /scratch/pcarroll/its254/test/mytest.c:12

Comments

Nick Clifton Feb. 6, 2018, 3:50 p.m. | #1
Hi Paul,

  Patch approved and applied.

  Note - for future submissions - it is generally better to supply
  the changelog entry as plain text, rather than a context diff, as
  they almost never apply cleanly to the sources.

Cheers
  Nick

Patch

diff -ruap a/bfd/dwarf2.c b/bfd/dwarf2.c
--- a/bfd/dwarf2.c	2018-01-03 01:14:20.000000000 -0800
+++ b/bfd/dwarf2.c	2018-01-30 07:35:28.776103173 -0800
@@ -2788,11 +2788,13 @@  lookup_symbol_in_variable_table (struct
 }
 
 static bfd_boolean
-find_abstract_instance_name (struct comp_unit *unit,
-			     bfd_byte *orig_info_ptr,
-			     struct attribute *attr_ptr,
-			     const char **pname,
-			     bfd_boolean *is_linkage)
+find_abstract_instance (struct comp_unit *unit,
+			bfd_byte *orig_info_ptr,
+			struct attribute *attr_ptr,
+			const char **pname,
+			bfd_boolean *is_linkage,
+			char **filename_ptr,
+			int *linenumber_ptr)
 {
   bfd *abfd = unit->abfd;
   bfd_byte *info_ptr;
@@ -2942,8 +2944,9 @@  find_abstract_instance_name (struct comp
 		    }
 		  break;
 		case DW_AT_specification:
-		  if (!find_abstract_instance_name (unit, info_ptr, &attr,
-						    pname, is_linkage))
+		  if (!find_abstract_instance (unit, info_ptr, &attr,
+					       pname, is_linkage,
+					       filename_ptr, linenumber_ptr))
 		    return FALSE;
 		  break;
 		case DW_AT_linkage_name:
@@ -2956,6 +2959,13 @@  find_abstract_instance_name (struct comp
 		      *is_linkage = TRUE;
 		    }
 		  break;
+		case DW_AT_decl_file:
+		  *filename_ptr = concat_filename (unit->line_table,
+						   attr.u.val);
+		  break;
+		case DW_AT_decl_line:
+		  *linenumber_ptr = attr.u.val;
+		  break;
 		default:
 		  break;
 		}
@@ -3148,9 +3158,11 @@  scan_unit_for_symbols (struct comp_unit
 
 		case DW_AT_abstract_origin:
 		case DW_AT_specification:
-		  if (!find_abstract_instance_name (unit, info_ptr, &attr,
-						    &func->name,
-						    &func->is_linkage))
+		  if (!find_abstract_instance (unit, info_ptr, &attr,
+					       &func->name,
+					       &func->is_linkage,
+					       &func->file,
+					       &func->line))
 		    goto fail;
 		  break;
 
diff -ruap a/binutils/ChangeLog b/binutils/ChangeLog
--- a/binutils/ChangeLog	2018-01-29 01:11:16.000000000 -0800
+++ b/binutils/ChangeLog	2018-02-01 06:51:19.326477888 -0800
@@ -1,3 +1,8 @@ 
+2018-02-01  Paul Carroll  <pcarroll@codesourcery.com>
+
+	* bfd/dwarf2.c (find_abstract_name): Modified to return file and
+	line information in addition to name.
+
 2018-01-28  Nick Clifton  <nickc@redhat.com>
 
 	* README-how-to-make-a-release: Add note about checking gpg key