# On g++-sjlj.exe (GCC) 4.2.1-sjlj (mingw32 sjlj-unwind)
Using built-in specs.
Target: mingw32
Configured with: ../gcc-4.2.1/configure --with-gcc --enable-libgomp
--host=mingw32 --build=mingw32 --target=mingw32 --program-suffix=-sjlj
--with-arch=i486 --with-tune=generic --disable-werror --prefix=/mingw
--with-local-prefix=/mingw --enable-threads --disable-nls
--enable-languages=c,c++,fortran,objc,obj-c++,ada --disable-win32-registry
--enable-sjlj-exceptions --enable-libstdcxx-debug
--enable-cxx-flags=-fno-function-sections -fno-data-sections
--enable-version-specific-runtime-libs --disable-bootstrap
Thread model: win32
gcc version 4.2.1-sjlj (mingw32 sjlj-unwind)
# Also
# On gcc version 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)
<testcase1.cc>--------------------------------
#include <stdio.h>
#include <signal.h>
void signal_handler(int signo) {
fprintf(stderr,"signaled\n");
throw 1;
}
int main()
{ signal(SIGSEGV,signal_handler);
try {
printf((char*)9); //<---(A)
}
catch(...) {
fprintf(stderr,"exception caught");
}
}
<testcase2.cc>-----------------------------------
#include <stdio.h>
#include <signal.h>
void signal_handler(int signo) {
fprintf(stderr,"signaled\n");
throw 1;
}
int main()
{ signal(SIGSEGV,signal_handler);
try {
*(int*)0 = 0; //<---(B)
}
catch(...) {
fprintf(stderr,"exception caught");
}
}
<disassembled main()-testcase2.cc>------------
//compiled as: g++sjlj testcase2.cc -g //gcc 4.2.1
int main()
4013f0: 8d 4c 24 04 lea 0x4(%esp),%ecx
4013f4: 83 e4 f0 and $0xfffffff0,%esp
4013f7: ff 71 fc pushl 0xfffffffc(%ecx)
4013fa: 55 push %ebp
4013fb: 89 e5 mov %esp,%ebp
4013fd: 51 push %ecx
4013fe: 83 ec 14 sub $0x14,%esp
401401: e8 6a ff ff ff call 401370 <__main>
{ signal(SIGSEGV,signal_handler);
401406: c7 44 24 04 34 14 40 movl $0x401434,0x4(%esp)
40140d: 00
40140e: c7 04 24 0b 00 00 00 movl $0xb,(%esp)
401415: e8 46 7b 00 00 call 408f60 <signal>
try {
*(int*)0 = 0; //<---(B)
40141a: b8 00 00 00 00 mov $0x0,%eax
40141f: c7 00 00 00 00 00 movl $0x0,(%eax)
401425: b8 00 00 00 00 mov $0x0,%eax
}
catch(...) {
fprintf(stderr,"exception caught");
}
}
40142a: 83 c4 14 add $0x14,%esp
40142d: 59 pop %ecx
40142e: 5d pop %ebp
40142f: 8d 61 fc lea 0xfffffffc(%ecx),%esp
401432: c3 ret
--------------------------------------------------------
<testcase1.cc> and <testcase2.cc> are identical except for (A),(B).
For <testcase1.cc>, <testcase2.cc> common:
Both (A) and (B) are supposed to throw no exception in C++ semantics. So no
need to generate the codes(<C1> hereafter) for adjusting the call site value
for (A),(B).
And the hole try block is supposed to throw no exception in C++ semantics. So
no need to generate the codes(<C2>) for the catch block at all.
But Gcc generates codes differently: (Regardless of optimization)
For <testcase1.cc>, Gcc generates the codes of both <C1>,<C2>
while for <testcase2.cc>, none as shown in <disassembled main()-testcase2.cc>,
which crashs testcase2.
Are C++ exceptions considered to be thrown from extern "C" functions (under
some conditions) but not from signal handlers? If so, it matters as in the tese
cases above where C++ exceptions can be thrown from signal handlers.
Adding an option would be nice.
Microsoft VisualC++ has similar problem when optimizing with -EHs option.
But option -EHa forces the compiler to generate proper codes (regardless of
optimization), which makes the traslation from Windows exception to C++
exception safe.
--
Summary: (exception handling) bad/inconsistent code generation
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: darkxun at paran dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33900
