Hi Folks,
On the Darwin aarch64 port, we have a number of cleanup test fails (pretty much
corresponding to the [still open]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39244). However, let’s assume
that bug could be a red herring..
the underlying reason is missing CFI for the set of the FP which [with Darwin’s
LLVM libunwind impl.] breaks the unwind through the function that triggers a
signal.
———
taking one of the functions in cleanup-8.C (say fn1) which contains calls.
what I am seeing is something like:
__ZL3fn1v:
LFB28:
; BLOCK 2, count:1073741824 (estimated locally) seq:0
; PRED: ENTRY [always] count:1073741824 (estimated locally, freq 1.0000)
(FALLTHRU)
stp x29, x30, [sp, -32]!
// LCFI; or .cfi_xxx is present
mov x29, sp
// *** NO LCFI (or .cfi_cfa_xxxx when that is enabled)
str x19, [sp, 16]
// LCFI / .cfi_xxxx is present.
adrp x19, __ZL3fn4i@PAGE
add x19, x19, __ZL3fn4i@PAGEOFF;momd
mov x1, x19
mov w0, 11
bl _signal
<snip>
———
The reason seems to be that, in expand_prolog, emit_frame_chain is true (as we
would expect, given that this function makes calls). However
‘frame_pointer_needed' is false, so that the call to aarch64_add_offset() [line
aarch64.cc:10405] does not add CFA adjustments to the load of x29.
———
I have currently worked around this by defining a TARGET_FRAME_POINTER_REQUIRED
which returns true unless the function is a leaf (if that’s the correct
solution, then all is fine).
———
However, it does seem odd that the existing code sets up the FP, but never
produces any CFA for it.
So is this a possible bug, or just that I misunderstand the relevant set of
circumstances?
thanks.
Iain
