BUG? -fomit-frame-pointer and exceptions or setjmp/longjmp

[Nix]

On Sun, 2 Jun 2002, Richard Henderson said:
> On Mon, Jun 03, 2002 at 03:29:31AM +0600, Denis Zaitsev wrote:
>> If gcc is built with the -fomit-frame-pointer in the environment's
>> CXXFLAGS, then we have a dead exception handling mechanics - a c++
>> program, compiled with such a gcc, can't catch any of an exceptions it
>> throws.
> 
> If true, that's a bug.  The frame pointer is NOT necessary to
> throw or catch exceptions.

I see similar things happening inside GiNaC-1.0.8, on an i586, only when
GiNaC is built with -fomit-frame-pointer:

loki 506 /usr/packages/GiNaC/i586-loki/check% ./exams 
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This GDB was configured as "i586-pc-linux-gnu"...(no debugging symbols found)...
(gdb) run
Starting program: /usr/packages/GiNaC/i586-loki/check/.libs/lt-exams 
(no debugging symbols found)...
Program received signal SIGSEGV, Segmentation fault.
0x402b1b16 in uw_frame_state_for (context=0xbffff360, fs=0xbffff2a0) at /usr/packages/gcc/3.1/gcc/unwind-dw2.c:910
910           MD_FALLBACK_FRAME_STATE_FOR (context, fs, success);
(gdb) bt
#0  0x402b1b16 in uw_frame_state_for (context=0xbffff360, fs=0xbffff2a0) at /usr/packages/gcc/3.1/gcc/unwind-dw2.c:910
#1  0x402b2108 in _Unwind_RaiseException (exc=0x81952a0) at /usr/packages/gcc/3.1/gcc/unwind.inc:93
#2  0x40289d48 in __cxa_throw (obj=0x81952a0, tinfo=0x402ada20, dest=0x402ada20 <globals_static>)
    at /usr/packages/gcc/3.1/libstdc++-v3/libsupc++/eh_throw.cc:72
#3  0x40116346 in GiNaC::power::eval(int) const () from /usr/packages/GiNaC/i586-loki/ginac/.libs/libginac-1.0.so.0
#4  0x4005fa8c in GiNaC::ex::construct_from_basic(GiNaC::basic const&) () from /usr/packages/GiNaC/i586-loki/ginac/.libs/libginac-1.0.so.0
#5  0x08060788 in std::__simple_alloc<GiNaC::ex, std::__default_alloc_template<true, 0> >::deallocate(GiNaC::ex*, unsigned) ()
#6  0x404a67f9 in __libc_start_main () from /lib/libc.so.6
#7  0xf0e48350 in ?? ()

I've isolated the throw that causes the crash, but haven't finished
trimming the thing down to a reproducible testcase of sane size. (The
throw at fault is on line 345 of power.cpp, the pow(0,0)-undefined
error case.)

As the trace shows, this crash occurs during unwinding, the presence or
absence of a catch is irrelevant. I'm rather wondering why we're hitting
MD_FALLBACK_FRAME_STATE_FOR at all: perhaps there's a problem in FDE
generation or something. (The fallback looks, er, odd to my eyes: diffing
assembler opcodes by hand just looks *ugly*.)

(Note that there are constructors, MI, and inlined functions at play
here.)


Tracking this down some more is on my to-do list if nobody else gets
there first: it might be related to the huge mass of g++ test failures
(in which exception throwing crashes) you get if GCC is built with
-fomit-frame-pointer.

-- 
`What happened?'
                 `Nick shipped buggy code!'
                                             `Oh, no dinner for him...'