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Date:	Thu, 30 Nov 2006 13:30:51 -0500
From:	"Lev Bishop" <lev DOT bishop AT gmail DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: isnan() causes segfault
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On 11/30/06, Eric Lilja wrote:
> If compiled with:
> $ g++ -Wall -Wextra -std=c++98 -pedantic -g isnantest.cpp -o run
> (those are the flags we have been using in this course).
> But it doesn't stackdump if compiled simply with:
> $ make isnantest
> g++     isnantest.cpp   -o isnantest

I was able to reproduce this behaviour.

There seems to be a difference in the generated assembler.
The -std=c++98 seems to be the only switch that matters.
Here is a diff. File isnantest2.s is the stackdumping one (ie the one
with -std=c++98)

--- isnantest.s 2006-11-30 13:14:12.718750000 -0500
+++ isnantest2.s        2006-11-30 13:26:55.984375000 -0500
@@ -1,4 +1,4 @@
-       .file   "isnantest.cpp"
+       .file   "isnantest2.cpp"
        .def    ___main;        .scl    2;      .type   32;     .endef
        .text
        .align 2
@@ -47,12 +47,9 @@
        movl    %esp, %ebp
        subl    $8, %esp
        movl    8(%ebp), %eax
-       movl    %eax, -4(%ebp)
-       fildl   -4(%ebp)
-       fstps   (%esp)
-       call    ___isnanf
+       movl    %eax, (%esp)
+       call    __ZN9__gnu_cxx5isnanIiEEiT_
        leave
        ret
-       .def    ___isnanf;      .scl    3;      .type   32;     .endef
        .def    __ZN9__gnu_cxx15__capture_isnanIiEEiT_; .scl    3;
 .type   32;     .endef
        .def    __ZN9__gnu_cxx5isnanIiEEiT_;    .scl    3;      .type   32;
.endef

Lev

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