How do I disable tailcall optimizations in gcc

Question

Hi all,

Wondering if anyone knows the flag for gcc to disable tailcall optimizations. Basically in a tailcall optimization, gcc will replace a stack frame when the return value from a called function is passed through (via return) or nothing else happens in the function.

That is, in

 void main() {
     foo();
 }

 void foo() {
     bar();
 }

 void bar() {
     /* at this point in code, the foo() stack frame no longer exists! */    
 }

When foo calls bar, gcc emits code that replaces the stack frame for foo, rather than adding a new stack frame.

My company has a stack unwinder that can print out a stack trace from any point in code. tailcall optimization makes stack frames disappear, which can confuse the stack trace somewhat.

I am compiling for x86-64 using gcc4.3.

Thanks in advance! P

Answer 1

GCC manual:

   -foptimize-sibling-calls
       Optimize sibling and tail recursive calls.

       Enabled at levels -O2, -O3, -Os.

So either compile with -O0/-O1, or use -fno-optimize-sibling-calls.

Answer 2

Untested: -fno-optimize-sibling-calls

http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html