gnu/packages/patches/jamvm-2.0.0-opcode-guard.patch

   1 From ca11b53896365c948426974cb90e8f71c70d123b Mon Sep 17 00:00:00 2001
   2 From: Simon South <simon@simonsouth.net>
   3 Date: Sun, 31 May 2020 20:36:43 -0400
   4 Subject: [PATCH] Guard floating-point opcodes with explicit memory barrier
   5
   6 ---
   7  src/interp/engine/interp-inlining.h | 11 ++++++++++-
   8  1 file changed, 10 insertions(+), 1 deletion(-)
   9
  10 diff --git a/src/interp/engine/interp-inlining.h b/src/interp/engine/interp-inlining.h
  11 index 3339b0e..4ee5c5a 100644
  12 --- a/src/interp/engine/interp-inlining.h
  13 +++ b/src/interp/engine/interp-inlining.h
  14 @@ -78,8 +78,17 @@
  15     4.3, we need to insert a label, and ensure its address
  16     is taken (to stop it being optimised out).  However,
  17     this reduces performance on PowerPC by approx 1 - 2%.
  18 +
  19 +   With gcc 5 and newer an asm statement with a "memory"
  20 +   clobber argument explicitly sets a memory barrier for the
  21 +   compiler, preventing it from reordering memory accesses
  22 +   in a way that breaks decaching.
  23  */
  24 -#if (__GNUC__ == 4) && (__GNUC_MINOR__ >= 3)
  25 +#if (__GNUC__ > 4)
  26 +#define DEF_GUARD_TABLE(level) /* none */
  27 +#define GUARD(opcode, level)   __asm__("" ::: "memory");
  28 +#define GUARD_TBLS             /* none */
  29 +#elif (__GNUC__ == 4) && (__GNUC_MINOR__ >= 3)
  30  #define DEF_GUARD_TABLE(level) DEF_HANDLER_TABLE(level, GUARD)
  31  #define GUARD(opcode, level)   label(opcode, level, GUARD)
  32  #define GUARD_TBLS             , HNDLR_TBLS(GUARD)
  33 --
  34 2.26.2
  35