[Qemu-devel] [PATCH 2/2] monitor: QEMU Monitor Instruction Disassembly Incorrect for PowerPC LE Mode

[Tom Musta <tommusta@gmail.com>]

The monitor support for disassembling instructions does not honor the MSR[LE]
bit for PowerPC processors.

This change enhances the monitor_disas() routine by supporting a flag bit
for Little Endian mode.  Bit 16 is used since that bit was used in the
analagous guest disassembly routine target_disas().

Also, to be consistent with target_disas(), the disassembler bfd_mach field
can be passed in the flags argument.

Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Tom Musta <tommusta@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
---
V2: Look specifically at bit 16 for LE.  Support machine configuration in flags.
V3: Changed documentation of 'flags' argument to simply refer to the target_disas
  description (per Peter Maydell's review).
V4: Corrections to comments.

The bug can be easily observed by dumping the first few instructions of an
interrupt vector (0x300 is the Data Storage Interrupt handler in PPC)

  (qemu) xp/8i 0x300
  0x0000000000000300:  .long 0x60
  0x0000000000000304:  lhzu    r18,-19843(r3)
  0x0000000000000308:  .long 0x60
  0x000000000000030c:  lhzu    r18,-20099(r2)
  0x0000000000000310:  lwz     r0,11769(0)
  0x0000000000000314:  lhzu    r23,8317(r2)
  0x0000000000000318:  .long 0x7813427c
  0x000000000000031c:  lbz     r0,19961(0)

With the patch applied, the disassembly now looks correct:

  (qemu) xp/8i 0x300
  0x0000000000000300:  nop
  0x0000000000000304:  mtsprg  2,r13
  0x0000000000000308:  nop
  0x000000000000030c:  mfsprg  r13,1
  0x0000000000000310:  std     r9,128(r13)
  0x0000000000000314:  mfspr   r9,896
  0x0000000000000318:  mr      r2,r2
  0x000000000000031c:  std     r10,136(r13)

 disas.c   |   14 ++++++++++++--
 monitor.c |    4 ++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/disas.c b/disas.c
index 1397167..44a019a 100644
--- a/disas.c
+++ b/disas.c
@@ -445,6 +445,8 @@ monitor_fprintf(FILE *stream, const char *fmt, ...)
     return 0;
 }
 
+/* Disassembler for the monitor.
+   See target_disas for a description of flags. */
 void monitor_disas(Monitor *mon, CPUArchState *env,
                    target_ulong pc, int nb_insn, int is_physical, int flags)
 {
@@ -485,11 +487,19 @@ void monitor_disas(Monitor *mon, CPUArchState *env,
     s.info.mach = bfd_mach_sparc_v9b;
 #endif
 #elif defined(TARGET_PPC)
+    if (flags & 0xFFFF) {
+        /* If we have a precise definition of the instruction set, use it. */
+        s.info.mach = flags & 0xFFFF;
+    } else {
 #ifdef TARGET_PPC64
-    s.info.mach = bfd_mach_ppc64;
+        s.info.mach = bfd_mach_ppc64;
 #else
-    s.info.mach = bfd_mach_ppc;
+        s.info.mach = bfd_mach_ppc;
 #endif
+    }
+    if ((flags >> 16) & 1) {
+        s.info.endian = BFD_ENDIAN_LITTLE;
+    }
     print_insn = print_insn_ppc;
 #elif defined(TARGET_M68K)
     print_insn = print_insn_m68k;
diff --git a/monitor.c b/monitor.c
index 342e83b..3ae561b 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1309,6 +1309,10 @@ static void memory_dump(Monitor *mon, int count, int format, int wsize,
             }
         }
 #endif
+#ifdef TARGET_PPC
+        flags = msr_le << 16;
+        flags |= env->bfd_mach;
+#endif
         monitor_disas(mon, env, addr, count, is_physical, flags);
         return;
     }
-- 
1.7.1