17.9.12 Generating Code for Profiling

These macros will help you generate code for profiling.

Macro: FUNCTION_PROFILER (file, labelno)

A C statement or compound statement to output to file some assembler code to call the profiling subroutine mcount.

The details of how mcount expects to be called are determined by your operating system environment, not by GCC. To figure them out, compile a small program for profiling using the system’s installed C compiler and look at the assembler code that results.

Older implementations of mcount expect the address of a counter variable to be loaded into some register. The name of this variable is ‘LP’ followed by the number labelno, so you would generate the name using ‘LP%d’ in a fprintf.

Macro: PROFILE_HOOK

A C statement or compound statement to output to file some assembly code to call the profiling subroutine mcount even the target does not support profiling.

Macro: NO_PROFILE_COUNTERS

Define this macro to be an expression with a nonzero value if the mcount subroutine on your system does not need a counter variable allocated for each function. This is true for almost all modern implementations. If you define this macro, you must not use the labelno argument to FUNCTION_PROFILER.

Macro: PROFILE_BEFORE_PROLOGUE

Define this macro if the code for function profiling should come before the function prologue. Normally, the profiling code comes after.

Target Hook: bool TARGET_KEEP_LEAF_WHEN_PROFILED (void)

This target hook returns true if the target wants the leaf flag for the current function to stay true even if it calls mcount. This might make sense for targets using the leaf flag only to determine whether a stack frame needs to be generated or not and for which the call to mcount is generated before the function prologue.