https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110069
Bug ID: 110069
Summary: [Perf] -finstrument-functions causes program size to
double
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: chipweinberger at jamcorder dot com
Target Milestone: ---
Created attachment 55228
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55228&action=edit
Assembly comparison with and without finstrument functions
Hello,
First time issue filer here.
First some context: I am using -finstrument-functions to implement a "stack
mirror" feature on the ESP32 microcontroller from Espressif. This mirror is
logged after detecting stack corruption, and it is incrediblly useful for
debugging.
Unfortunately, -finstrument-functions causes the program size to double, using
100KB extra of internal SRAM (over 20% of the entire MCUs memory), meaning most
people cannot even enable this feature because spare ram is usually very
scarce.
The main problem is the function signature of __cyg_profile_func_enter. ~35
bytes of instructions are needed to set up the 2 function arguments, and these
35 bytes need to be inserted into *every* function. This is a major cost for
both performance and memory.
void __cyg_profile_func_enter(void *func, void *callsite)
These arguments are not needed by us. We can traverse the stack ourself.
I am hoping we can consider a new flag, -function-entry-exit-hooks, with a much
simpler function signature:
void __func_hook_entry(void)
void __func_hook_exit(void)
Without the arguments, each function only needs a simple 'call' instruction.
This would be incredibly useful for us, and I imagine a lot of other people as
well.
Thanks,
Chip
