When a variable length array is defined in a loop, and its size is specified with a const variable, gcc -O3 (and -Os) produces a call of alloca() without specifying the size argument (eax in my case). This causes stack overflow. $ cat test.c int const n = 4096; void g(int* p); void f() { for(;;) { int a[n]; g(a); } } $ gcc -S -O3 -o - test.c (snip) .globl _f .def _f; .scl 2; .type 32; .endef _f: pushl %ebp movl %esp, %ebp pushl %esi pushl %ebx subl $16, %esp .p2align 4,,7 L2: movl %esp, %ebx call __alloca (snip) $ gcc -v Using built-in specs. Target: i686-pc-cygwin Configured with: /gnu/gcc/releases/packaging/4.3.4-3/gcc4-4.3.4-3/src/gcc-4.3.4/configure --srcdir=/gnu/gcc/releases/packaging/4.3.4-3/gcc4-4.3.4-3/src/gcc-4.3.4 --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --libexecdir=/usr/lib --datadir=/usr/share --localstatedir=/var --sysconfdir=/etc --infodir=/usr/share/info --mandir=/usr/share/man --datadir=/usr/share --infodir=/usr/share/info --mandir=/usr/share/man -v --with-gmp=/usr --with-mpfr=/usr --enable-bootstrap --enable-version-specific-runtime-libs --with-slibdir=/usr/bin --libexecdir=/usr/lib --enable-static --enable-shared --enable-shared-libgcc --disable-__cxa_atexit --with-gnu-ld --with-gnu-as --with-dwarf2 --disable-sjlj-exceptions --enable-languages=ada,c,c++,fortran,java,objc,obj-c++ --disable-symvers --enable-libjava --program-suffix=-4 --enable-libgomp --enable-libssp --enable-libada --enable-threads=posix --with-arch=i686 --with-tune=generic --enable-libgcj-sublibs CC=gcc-4 CXX=g++-4 CC_FOR_TARGET=gcc-4 CXX_FOR_TARGET=g++-4 GNATMAKE_FOR_TARGET=gnatmake GNATBIND_FOR_TARGET=gnatbind AS=/opt/gcc-tools/bin/as.exe AS_FOR_TARGET=/opt/gcc-tools/bin/as.exe LD=/opt/gcc-tools/bin/ld.exe LD_FOR_TARGET=/opt/gcc-tools/bin/ld.exe --with-ecj-jar=/usr/share/java/ecj.jar Thread model: posix gcc version 4.3.4 20090804 (release) 1 (GCC)