Re: [RFC] Getting LTO incremental linking work

[Tom de Vries <Tom_deVries at mentor dot com>]

On 26/11/15 00:07, Jan Hubicka wrote:
> (flinker_output): New flag.

Hi,

this seems to have cause a regression when using a compiler configured 
for offloading (giving ~1000 fails in libgomp testing).

For test-case libgomp.c/examples-4/array_sections-3.c, we enter run_gcc 
in lto-wrapper with args:
...
Breakpoint 1, run_gcc (argc=4, argv=0x7fffffffde68) at 
src/gcc-gomp-4_0-branch/gcc/lto-wrapper.c:897
897       char *list_option_full = NULL;
(gdb) p argv[0]
$8 = 0x7fffffffe104 "lto-wrapper"
(gdb) p argv[1]
$9 = 0x7fffffffe1af "-fresolution=array_sections-3.res"
(gdb) p argv[2]
$10 = 0x7fffffffe1d1 "-flinker-output=exec"
(gdb) p argv[3]
$11 = 0x7fffffffe1e6 "array_sections-3.o"
...

And here (cc-ing author of this bit) we decide that -flinker-output=exec 
is a file:
...
/* If object files contain offload sections, but do not contain LTO
   sections,
   then there is no need to perform a link-time recompilation, i.e.
   lto-wrapper is used only for a compilation of offload images. */
if (have_offload && !have_lto)
  {
    for (i = 1; i < argc; ++i)
      if (strncmp (argv[i], "-fresolution=",
		   sizeof ("-fresolution=") - 1))
	{
	  char *out_file;
	  /* Can be ".o" or ".so". */
	  char *ext = strrchr (argv[i], '.');
	  if (ext == NULL)
	    out_file = make_temp_file ("");
	  else
	    out_file = make_temp_file (ext);
	  /* The linker will delete the files we give it, so make
	     copies. */
	  copy_file (out_file, argv[i]);
	  printf ("%s\n", out_file);
	}
    goto finish;
  }
...

And try to copy it:
...
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff783d7e0 in feof () from /lib/libc.so.6
(gdb) bt
#0  0x00007ffff783d7e0 in feof () from /lib/libc.so.6
#1  0x0000000000406ff5 in copy_file (dest=0x71cdd0 "/tmp/ccL6HCCe", 
src=0x7fffffffe1d1 "-flinker-output=exec")
    at lto-wrapper.c:769
#2  0x00000000004080b7 in run_gcc (argc=4, argv=0x7fffffffde68) at 
gcc/lto-wrapper.c:1109
#3  0x0000000000409873 in main (argc=4, argv=0x7fffffffde68) at 
gcc/lto-wrapper.c:1396
...

Thanks,
- Tom