On 8/3/20 10:35 PM, Josh Poimboeuf wrote:
On Mon, Aug 03, 2020 at 01:13:14PM +0100, Julien Thierry wrote:
On 7/31/20 3:04 PM, Josh Poimboeuf wrote:
On Fri, Jul 31, 2020 at 08:00:58AM +0100, Julien Thierry wrote:
+ cfa->offset = hint->sp_offset;
+ insn->cfi.hint_type = hint->type;
+ insn->cfi.end = hint->end;
+
+ insn->cfi.sp_only = hint->type == ORC_TYPE_REGS || hint->type ==
ORC_TYPE_REGS_IRET;
What does "sp" mean here in sp_only?
Stack pointer, like in CFI_SP. When objtool encounters one of these hints,
it starts to only track the stack frame with the stack pointer (no BP, no
drap register, no move to temporary registers). Just trying to make some
sense of this corner case.
I think that's not quite right, because ORC_TYPE_CALL could also be
"sp_only" in some cases, by that definition.
But in that case the code will still track when/if the CFI becomes pointed
to by BP.
The call to update_cfi_state_regs() is really regs-specific, not
sp-specific.
I must admit I don't really understand what "regs" is and why exactly such
an exception in stack state tracking is made where only operations to SP are
taken into account.
"regs" is a special type of stack frame, usually for asm entry code,
where the frame is actually an instance of 'struct pt_regs'. So if
there's a variable associated it with it, maybe it should have "regs" in
the name.
Though I think non-x86 arches will also have regs frames, so would it
make sense to just make the unwind hint types a global multiarch thing?
They could be renamed to UNWIND_HINT_TYPE_REGS{_PARTIAL}. Then there
wouldn't really be a need for the "sp_only" thing.
If having regs frame means having a pt_regs on the stack when procedure
calls/return, then yes this will probably be the case on most archs (it
is for arm64 at least.
However in that case, arm64 still builds a stack frame and sets the
frame pointer, so only handling SP operations doesn't make much sense
for arm64.
Also, things like ORC_TYPE_REGS_IRET don't have a use for arm64 (but
maybe for other non-x86 arches it does?)
In the end that's why I left the unwind hint types as arch defined. It
seems like every arch will have their specific semantics they might want
to let objtool know about.
--
Julien Thierry
