Re: [PATCH v2] aarch64: Add split-stack initial support

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

Adhemerval Zanella wrote:
  
Sorry for the late reply - but I think it's getting there. A few more comments:

+  /* If function uses stacked arguments save the old stack value so morestack
+     can return it.  */
+  reg11 = gen_rtx_REG (Pmode, R11_REGNUM);
+  if (cfun->machine->frame.saved_regs_size
+      || cfun->machine->frame.saved_varargs_size)
+    emit_move_insn (reg11, stack_pointer_rtx);

This doesn't look right - we could have many arguments even without varargs or
saved regs.  This would need to check varargs as well as ctrl->args.size (I believe
that is the size of the arguments on the stack). It's fine to omit this optimization
in the first version - we already emit 2-3 extra instructions for the check anyway.


+void
+aarch64_split_stack_space_check (rtx size, rtx label)
{
+  rtx mem, ssvalue, cc, cmp, jump, temp;
+  rtx requested = gen_reg_rtx (Pmode);
+  /* Offset from thread pointer to __private_ss.  */
+  int psso = 0x10;
+
+  /* Load __private_ss from TCB.  */
+  ssvalue = gen_rtx_REG (Pmode, R9_REGNUM);

ssvalue doesn't need to be a hardcoded register.

+  emit_insn (gen_aarch64_load_tp_hard (ssvalue));
+  mem = gen_rtx_MEM (Pmode, plus_constant (Pmode, ssvalue, psso));
+  emit_move_insn (ssvalue, mem);
+
+  temp = gen_rtx_REG (Pmode, R10_REGNUM);
+
+  /* And compare it with frame pointer plus required stack.  */
+  size = force_reg (Pmode, size);
+  emit_move_insn (requested, gen_rtx_MINUS (Pmode, stack_pointer_rtx, size));
+
+  /* Jump to __morestack call if current __private_ss is not suffice.  */
+  cc = aarch64_gen_compare_reg (LT, temp, ssvalue);

This uses X10, but where is it set???

+  cmp = gen_rtx_fmt_ee (GEU, VOIDmode, cc, const0_rtx);
+  jump = emit_jump_insn (gen_condjump (cmp, cc, label));
+  JUMP_LABEL (jump) = label;
+}

So neither X10 nor X12 are set before potentially calling __morestack, so I don't
think it will work. Could this be causing the crash you mentioned?

Wilco