diff mbox series

[SH] Fix mac.w insn simulation for SH2 and above

Message ID ea983e6d997f4d793fa7486b363a66b2345a1bb5.camel@gmail.com
State New
Headers
Series [SH] Fix mac.w insn simulation for SH2 and above |

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Commit Message

Oleg Endo Aug. 2, 2026, 1:53 p.m. UTC 
  Hi,

The simulator currently implements only the SH1 version of the mac.w
instruction.  On SH1 the MACH:MACL accumulator register is only 42-bit.  It
was extended to 64-bit on SH2 and every variant that followed after.

The issue probably never showed up because GCC hasn't been able to emit the
SH integer mac instructions.  I ran into this because I was trying to do
exactly that and while running some tests on sh-sim.

The attached patch uses the bfd_mach field to distinguish between SH1 and
not-SH1 in the simulation of the mac.w instruction, in a similar way as it's
already been done for some SH2A instructions.


OK to commit & push?

Best regards,
Oleg Endo
diff mbox series

Patch

From 6b07e3daa73acac1d1800c94cdfae0b83509f2d1 Mon Sep 17 00:00:00 2001
From: Oleg Endo <olegendo@gcc.gnu.org>
Date: Sun, 2 Aug 2026 19:37:21 +0900
Subject: [PATCH] sim/sh: fix mac.w insn for SH2+

On SH1 the MACH:MACL accumulator is only 42 bits wide.  On SH2 and above it's 64
bits wide.  Emulate the corresponding behavior based on the bfd_mach field.
---
 sim/sh/interp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/sim/sh/interp.c b/sim/sh/interp.c
index c8c2a74..cc4ae2c 100644
--- a/sim/sh/interp.c
+++ b/sim/sh/interp.c
@@ -1197,8 +1197,11 @@  macw (int *regs, unsigned char *memory, int n, int m, int endianw)
       long mach;
       /* Add to MACH the sign extended product, and carry from low sum.  */
       mach = MACH + (-(prod < 0)) + ((unsigned long) sum < prod);
-      /* Sign extend at 10:th bit in MACH.  */
-      MACH = (mach & 0x1ff) | -(mach & 0x200);
+      /* SH1:  MACH:MACL is 42 bits wide, sign extend at the 10:th bit in MACH.
+         SH2+: MACH:MACL is 64 bits wide.  */
+      if (saved_state.asregs.bfd_mach == bfd_mach_sh)
+	mach = (mach & 0x1ff) | -(mach & 0x200);
+      MACH = mach;
     }
   MACL = sum;
 }
--
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