6.6.1 Stack Overflow Checking

For most operating systems, gcc does not perform stack overflow checking by default. This means that if the main environment task or some other task exceeds the available stack space, then unpredictable behavior will occur. Most native systems offer some level of protection by adding a guard page at the end of each task stack. This mechanism is usually not enough for dealing properly with stack overflow situations because a large local variable could "jump" above the guard page. Furthermore, when the guard page is hit, there may not be any space left on the stack for executing the exception propagation code. Enabling stack checking avoids such situations.

To activate stack checking, compile all units with the gcc option -fstack-check. For example:

$ gcc -c -fstack-check package1.adb

Units compiled with this option will generate extra instructions to check that any use of the stack (for procedure calls or for declaring local variables in declare blocks) does not exceed the available stack space. If the space is exceeded, then a Storage_Error exception is raised.

For declared tasks, the default stack size is defined by the GNAT runtime, whose size may be modified at bind time through the -d bind switch (Switches for gnatbind). Task specific stack sizes may be set using the Storage_Size pragma.

For the environment task, the stack size is determined by the operating system. Consequently, to modify the size of the environment task please refer to your operating system documentation.