fomit-frame-pointer, Oy

Determines whether EBP is used as a general-purpose register in optimizations.

Architecture Restrictions

Option /Oy[-] is only available on IA-32 architecture. IA-32 architecture is only supported for C++.

Syntax

Linux:

-fomit-frame-pointer

-fno-omit-frame-pointer

Windows:

/Oy (C++ only)

/Oy- (C++ only)

Arguments

None

Default

-fomit-frame-pointer
C++: or /Oy

EBP is used as a general-purpose register in optimizations.

However, the default can change depending on the following:

Linux

If option -O0 or -g is specified, the default is -fno-omit-frame-pointer.

Windows

C++: If option /Od is specified, the default is /Oy- .

Description

These options determine whether EBP is used as a general-purpose register in optimizations. Option -fomit-frame-pointer and option /Oy allows this use. Option -fno-omit-frame-pointer and option /Oy- disallows it.

Some debuggers expect EBP to be used as a stack frame pointer, and cannot produce a stack backtrace unless this is so. The -fno-omit-frame-pointer and the /Oy- option directs the compiler to generate code that maintains and uses EBP as a stack frame pointer for all functions so that a debugger can still produce a stack backtrace without doing the following:

The -fno-omit-frame-pointer option is set when you specify option -O0 or the -g option. The -fomit-frame-pointer option is set when you specify option -O1, -O2, or -O3.

For C++, the /Oy option is set when you specify the /O1, /O2, or /O3 option. Option /Oy- is set when you specify the /Od option.

Using the -fno-omit-frame-pointer or /Oy- option reduces the number of available general-purpose registers by 1, and can result in slightly less efficient code.

Note

Linux

There is currently an issue with GCC 3.2 exception handling. Therefore, the compiler ignores this option when GCC 3.2 is installed for C++ and exception handling is turned on (the default).

IDE Equivalent

Visual Studio: Optimization > Omit Frame Pointers

Eclipse: Optimization > Provide Frame Pointer

Alternate Options

Linux: -fp (this is a deprecated option)

Windows: None

See Also