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Date: Sat, 02 Mar 2013 21:23:15 +0100
From: Dimitry Andric <dim@FreeBSD.org>
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To: Andriy Gapon <avg@FreeBSD.org>, freebsd-hackers@FreeBSD.org
Subject: Re: clang generated code sometimes confuses fbt
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On 2013-03-02 18:52, Andriy Gapon wrote:
> on 02/03/2013 19:35 Andriy Gapon said the following:
>> Now, I am not quite sure why ctfconvert skips bpobj_iterate_impl in the
>> clang-generated code.  Seems like some sort of a bug in ctfconvert.
>
> It seems that gcc and clang put different names for symbol of type FILE:
> clang:
> readelf -a -W /usr/obj/usr/src/sys/TRANT/bpobj.o| fgrep -w FILE
>       1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS
> /usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/bpobj.c
>
> gcc:
> readelf -a -W /usr/obj/usr/src/sys/ODYSSEY/bpobj.o| fgrep -w FILE
>       1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS bpobj.c
>
> ctfconvert seems to compare this value with "bpobj.c" and so in the clang case
> it doesn't recognize the static symbols.
>
> Does my analysis seem reasonable?

Have you verified that ctfconvert does the right thing, if you modify
the FILE symbol to have just the filename?

Indeed, clang puts the original filename from the command line in the
.file directive, while gcc explicitly removes any directory names; see
contrib/gcc/toplev.c, around line 680:

   void
   output_file_directive (FILE *asm_file, const char *input_name)
   {
     int len;
     const char *na;

     if (input_name == NULL)
       input_name = "<stdin>";

     len = strlen (input_name);
     na = input_name + len;

     /* NA gets INPUT_NAME sans directory names.  */
     while (na > input_name)
       {
	if (IS_DIR_SEPARATOR (na[-1]))
	  break;
	na--;
       }
...

That "NA gets INPUT_NAME sans directory names" comment was inserted by
rms in r279. :-)  So I guess this is the way gcc has done it from the
start, but there is no explanation as to why rms chose to remove those
directory names.  I do not see the problem, except maybe for having
reproducible builds?

-Dimitry