On Tue, Feb 27, 2024 at 10:04:06AM +0100, Jakub Jelinek wrote:
> > I hope we at least avoid that at -O0, possibly also with -Og?
>
> r14-8495 fixed at least that.
>
> Of course, it can break debugging experience even when the noreturn function
> is compiled with -O2 but some or all callers of that are -O0 or -Og.
> So, if unlucky and e.g. abort function in glibc gets the
> no_callee_saved_registers treatment and actually uses some call saved
> registers, backtraces when something aborts will be worse or useless.
> And we don't even have any attribute which would tell gcc not to do that.
>
> So sure, another option is just revert the PR38534 changes.
For __libc_start_main, glibc surely just could use no_callee_saved_registers
attribute, because that is typically the outermost frame in backtrace,
there is no need to save those there.
And for kernel if it really wants it and nothing will use the backtraces,
perhaps the patch wouldn't need to be reverted completely but just guarded
the implicit no_callee_saved_registers treatment of noreturn
functions on -mcmodel=kernel or -fno-asynchronous-unwind-tables.
Jakub
