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

[Paul Carroll <pcarroll at codesourcery dot com>]

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

Attachment: proposed_patch
Description: Text document