Another GCC behavior that makes me angry: it produce wrong stack frames for leaf functions even if -fno-omit-frame-pointer is provided: Clang, GCC. GCC put previous frame pointer at wrong offset for leaf functions.
This cause broken stack traces:
PANIC: vm_page_fault: unhandled page fault in kernel space at 0xffffffff4a70e940, ip 0x100171978
Welcome to Kernel Debugging Land...
Thread 444 "app_server" running on CPU 0
Stack:
FP: 0x100a29e30
FP: 0x100a29f40, PC: 0x1001655f9 <kernel_riscv64> arch_debug_call_with_fault_handler + 91
FP: 0x100a29f90, PC: 0x1000ddb89 <kernel_riscv64> debug_call_with_fault_handler.localalias.7 + 129
FP: 0x100a2a020, PC: 0x1000df1c9 <kernel_riscv64> _ZL20kernel_debugger_loopPKcS0_Pvi + 299
FP: 0x100a2a090, PC: 0x1000df4b5 <kernel_riscv64> _ZL24kernel_debugger_internalPKcS0_Pvi + 135
FP: 0x100a2a0d0, PC: 0x1000df7fd <kernel_riscv64> panic + 101
FP: 0x100a2a200, PC: 0x100152bcd <kernel_riscv64> vm_page_fault + 541
FP: 0x100a2a2e0, PC: 0x100166591 <kernel_riscv64> STrap + 255
FP: 0x100a2a3e0, PC: 0x10016482d <kernel_riscv64> SVec + 77
FP: 0x100a2a3f0, PC: 0x100171977 <kernel_riscv64> strcpy + 15
FP: 0x8198cb80, PC: 0x100a2a4df <app_server_444_kstack> 0x44df // PC is really FP here and FP is garbage
FP: 0xde01d898, PC: 0x0 0x0
FP: 0x8198d3f0, PC: 0x8104b47f <slab area> 0x4b47f
FP: 0x0, PC: 0x2 0x2
kdebug>
I also have GCC some workarounds for code that works fine in Mini OS and Clang.
Someday I will probably throw away GCC and fully switch to Clang. GCC is terrible in all ways including ancient autotools build system that also cause troubles when crosscompiling on Haiku.
FreeBSD already switched to Clang.