In long mode, POP to memory will write a full 64-bit value.  However,
the call to gen_writeback() in gen_POP will use MO_32 because the
decoding table is incorrect.

The bug was latent until commit aea49fbb01a ("target/i386: use gen_writeback()
within gen_POP()", 2024-06-08), and then became visible because gen_op_st_v
now receives op->ot instead of the "ot" returned by gen_pop_T0.

Analyzed-by: Clément Chigot <chigot@adacore.com>
Fixes: 5e9e21bcc4d ("target/i386: move 60-BF opcodes to new decoder", 2024-05-07)
Tested-by: Clément Chigot <chigot@adacore.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/decode-new.c.inc | 2 +-
 target/i386/tcg/emit.c.inc       | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
index 0d846c32c22..d2da1d396d5 100644
--- a/target/i386/tcg/decode-new.c.inc
+++ b/target/i386/tcg/decode-new.c.inc
@@ -1717,7 +1717,7 @@ static const X86OpEntry opcodes_root[256] = {
     [0x8C] = X86_OP_ENTRYwr(MOV, E,v, S,w, op0_Mw),
     [0x8D] = X86_OP_ENTRYwr(LEA, G,v, M,v, nolea),
     [0x8E] = X86_OP_ENTRYwr(MOV, S,w, E,w),
-    [0x8F] = X86_OP_GROUPw(group1A, E,v),
+    [0x8F] = X86_OP_GROUPw(group1A, E,d64),
 
     [0x98] = X86_OP_ENTRY1(CBW,    0,v), /* rAX */
     [0x99] = X86_OP_ENTRYwr(CWD,   2,v, 0,v), /* rDX, rAX */
diff --git a/target/i386/tcg/emit.c.inc b/target/i386/tcg/emit.c.inc
index fc7477833bc..c6c2c7257b9 100644
--- a/target/i386/tcg/emit.c.inc
+++ b/target/i386/tcg/emit.c.inc
@@ -2788,6 +2788,8 @@ static void gen_POP(DisasContext *s, X86DecodedInsn *decode)
     X86DecodedOp *op = &decode->op[0];
     MemOp ot = gen_pop_T0(s);
 
+    /* Only 16/32-bit access in 32-bit mode, 16/64-bit access in long mode.  */
+    assert(ot == op->ot);
     if (op->has_ea || op->unit == X86_OP_SEG) {
         /* NOTE: order is important for MMU exceptions */
         gen_writeback(s, decode, 0, s->T0);
-- 
2.45.2

On 7/10/24 07:13, Paolo Bonzini wrote:
> In long mode, POP to memory will write a full 64-bit value.  However,
> the call to gen_writeback() in gen_POP will use MO_32 because the
> decoding table is incorrect.
> 
> The bug was latent until commit aea49fbb01a ("target/i386: use gen_writeback()
> within gen_POP()", 2024-06-08), and then became visible because gen_op_st_v
> now receives op->ot instead of the "ot" returned by gen_pop_T0.
> 
> Analyzed-by: Clément Chigot<chigot@adacore.com>
> Fixes: 5e9e21bcc4d ("target/i386: move 60-BF opcodes to new decoder", 2024-05-07)
> Tested-by: Clément Chigot<chigot@adacore.com>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
>   target/i386/tcg/decode-new.c.inc | 2 +-
>   target/i386/tcg/emit.c.inc       | 2 ++
>   2 files changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~