C++ exception handling broken if parts of libgcc are compiled using `-fomit-frame-pointer´

[Manfred Hollstein <manfredh at redhat dot com>]

Hi there,

Yesterday I  ran   "make bootstrap check"   on  i686-redhat6-linux-gnu
several   times on   the   same sources,   each  time  using different
BOOT_CFLAGS. It turned  out, that if  `-fomit-frame-pointer´ (FOFP) is
used, 8 additional failures in the g++ testsuite show up:

  FAIL: g++.eh/spec2.C  Execution test
  FAIL: g++.eh/spec3.C  Execution test
  FAIL: g++.eh/spec4.C  Execution test
  FAIL: g++.mike/dyncast1.C  Execution test
  FAIL: g++.mike/dyncast2.C  Execution test
  FAIL: g++.mike/eh33.C  Execution test
  FAIL: g++.mike/eh50.C  Execution test
  FAIL: g++.mike/eh51.C  Execution test

IIRC, somebody mentioned that the current exception handling mechanism
doesn't work if  the FOFP flag  is used. So I  rebuilt those  parts of
libgcc.a, which   depend  on proper  frame  handling, this  time using
`-fno-omit-frame-pointer´, and replaced those modules in libgcc.a.

Running the tests, which formerly crashed, terminated successfully now.

So, my question is:

  `Is "-fomit-frame-pointer" plus exception handling deprecated in
   general, or just on those platforms which are using the DWARF2
   unwinder?´

If the latter is true, I'd suggest we reset flag_omit_frame_pointer in
toplev.c emitting a suitable warning like this:

#if DWARF2_UNWIND_INFO
  if (flag_omit_frame_pointer && flag_exceptions)
    {
      warning ("-fomit-frame-pointer is incompatible with the exception handling mechanism on this target; disabling it");
      flag_omit_frame_pointer = 0;
    }
#endif

If this   isn't the way to  go,  we need to find  a  way to make sure,
libgcc.a  will   be generated  properly  regardless  of   BOOT_CFLAGS,
however.

Thoughts?

Cheers, manfred.