[Bug 1841990] Re: instruction 'denbcdq' misbehaving

[Mark Cave-Ayland]

That certainly sounds like progress. Did you see the follow up email
indicating the typo that I found in patch 6? It can be fixed by applying
the following diff on top:

diff --git a/target/ppc/dfp_helper.c b/target/ppc/dfp_helper.c
index c2d335e928..b801acbedc 100644
--- a/target/ppc/dfp_helper.c
+++ b/target/ppc/dfp_helper.c
@@ -1054,7 +1054,7 @@ static inline void dfp_set_sign_64(ppc_vsr_t *t, uint8_t 
sgn)
 static inline void dfp_set_sign_128(ppc_vsr_t *t, uint8_t sgn)
 {
     t->VsrD(0) <<= 4;
-    t->VsrD(0) |= (t->VsrD(0) >> 60);
+    t->VsrD(0) |= (t->VsrD(1) >> 60);
     t->VsrD(1) <<= 4;
     t->VsrD(1) |= (sgn & 0xF);
 }

Does that help any more tests to pass? Also the changes to the FP
register layout were made in QEMU 4.0 and so it seems to me that even if
some tests fail, if the results between QEMU 3.1 and QEMU git master
with the patchset applied are equivalent then we can assume that the
patchset functionality is correct.

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https://bugs.launchpad.net/bugs/1841990

Title:
  instruction 'denbcdq' misbehaving

Status in QEMU:
  New

Bug description:
  Instruction 'denbcdq' appears to have no effect.  Test case attached.

  On ppc64le native:
  --
  gcc -g -O -mcpu=power9 bcdcfsq.c test-denbcdq.c -o test-denbcdq
  $ ./test-denbcdq
  0x00000000000000000000000000000000
  0x0000000000000000000000000000000c
  0x22080000000000000000000000000000
  $ ./test-denbcdq 1
  0x00000000000000000000000000000001
  0x0000000000000000000000000000001c
  0x22080000000000000000000000000001
  $ ./test-denbcdq $(seq 0 99)
  0x00000000000000000000000000000064
  0x0000000000000000000000000000100c
  0x22080000000000000000000000000080
  --

  With "qemu-ppc64le -cpu power9"
  --
  $ qemu-ppc64le -cpu power9 -L [...] ./test-denbcdq
  0x00000000000000000000000000000000
  0x0000000000000000000000000000000c
  0x0000000000000000000000000000000c
  $ qemu-ppc64le -cpu power9 -L [...] ./test-denbcdq 1
  0x00000000000000000000000000000001
  0x0000000000000000000000000000001c
  0x0000000000000000000000000000001c
  $ qemu-ppc64le -cpu power9 -L [...] ./test-denbcdq $(seq 100)
  0x00000000000000000000000000000064
  0x0000000000000000000000000000100c
  0x0000000000000000000000000000100c
  --

  I started looking at the code, but I got confused rather quickly.
  Could be related to endianness? I think denbcdq arrived on the scene
  before little-endian was a big deal.  Maybe something to do with
  utilizing implicit floating-point register pairs...  I don't think the
  right data is getting to helper_denbcdq, which would point back to the
  gen_fprp_ptr uses in dfp-impl.inc.c (GEN_DFP_T_FPR_I32_Rc).  (Maybe?)

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