RFR: 8207345: AArch64: Trampoline generation code reads from uninitialized memory

[Andrew Haley]

On 07/16/2018 05:38 PM, Aleksey Shipilev wrote:
> Your choice, really. I used to frown about conditionals like this all around Hotspot, but then I
> started to see the appeal: you can clearly see (A && B && C) here, even if A, B, C are not trivial.
> But structurally, you immediately grasp that if A fails, we don't enter the block; if B fails, we
> don't enter the block, if C fails, we don't enter the block. It takes some time to read through
> chain of local variables to reach the same verdict.

I see.  I tried it, and I think your suggestions do help, and the
hybrid result is best of all:

  // We need a trampoline if branches are far.
  if (far_branches()) {
    // We don't want to emit a trampoline if C2 is generating dummy
    // code during its branch shortening phase.
    CompileTask* task = ciEnv::current()->task();
    if (task != NULL && is_c2_compile(task->comp_level()) &&
        Compile::current->in_scratch_emit_size()) {
      address stub = emit_trampoline_stub(offset(), entry.target());
      if (stub == NULL) {
        return NULL; // CodeCache is full
      }
    }

Thanks.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671