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Re: isnan() causes segfault

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
       .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_
-       .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;


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