From d73ce0f593fc9b1dfd482fd6b1b907af7918953d Mon Sep 17 00:00:00 2001
From: Gabe Black <gabe.black@gmail.com>
Date: Mon, 17 Jan 2022 00:27:23 -0800
Subject: [PATCH] arch-x86: Implement real mode far call.

Change-Id: I720a0b0e4aa227171c59804d899baba64b8d320b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55623
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
---
 src/arch/x86/isa/decoder/one_byte_opcodes.isa |  6 +-
 .../general_purpose/control_transfer/call.py  | 71 +++++++++++++++++++
 2 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/src/arch/x86/isa/decoder/one_byte_opcodes.isa b/src/arch/x86/isa/decoder/one_byte_opcodes.isa
index e36962154f..64e10bac5e 100644
--- a/src/arch/x86/isa/decoder/one_byte_opcodes.isa
+++ b/src/arch/x86/isa/decoder/one_byte_opcodes.isa
@@ -305,6 +305,7 @@
             0x1: CQO(rAv,rDv);
             0x2: decode MODE_SUBMODE {
                 0x0: UD2();
+                0x4: CALL_FAR_REAL(Iz);
                 default: WarnUnimpl::call_far_Ap();
             }
             0x3: WarnUnimpl::fwait(); //aka wait
@@ -568,7 +569,10 @@
                 0x0: INC(Ev);
                 0x1: DEC(Ev);
                 0x2: CALL_NEAR(Ev);
-                0x3: WarnUnimpl::call_far_Mp();
+                0x3: decode MODE_SUBMODE {
+                    0x4: CALL_FAR_REAL(Mz);
+                    default: WarnUnimpl::call_far_Mp();
+                }
                 0x4: JMP(Ev);
                 0x5: decode MODE_SUBMODE {
                     0x0: JMP_FAR(Mz);
diff --git a/src/arch/x86/isa/insts/general_purpose/control_transfer/call.py b/src/arch/x86/isa/insts/general_purpose/control_transfer/call.py
index 8000bc3e2a..8d11256f51 100644
--- a/src/arch/x86/isa/insts/general_purpose/control_transfer/call.py
+++ b/src/arch/x86/isa/insts/general_purpose/control_transfer/call.py
@@ -92,6 +92,77 @@ def macroop CALL_NEAR_P
     subi rsp, rsp, dsz, dataSize=ssz
     wripi t1, 0
 };
+
+def macroop CALL_FAR_REAL_I {
+    .function_call
+    .control_indirect
+
+    limm t1, imm, dataSize=8
+
+    # Multiply the data size by 8 to get the size of the offset in bits.
+    limm t3, dsz, dataSize=8
+    slli t3, t3, 3, dataSize=8
+
+    # Extract the selector from the far pointer.
+    srl t2, t1, t3, dataSize=8
+    zexti t2, t2, 15, dataSize=8
+    # Extract the offset from the far pointer.
+    zext t1, t1, t3, dataSize=8
+
+    # Compute the base.
+    slli t3, t2, 4, dataSize=8
+
+    # Make sure pushing the RIP will work after we push cs.
+    cda ss, [1, t0, rsp], "-env.dataSize * 2", addressSize=ssz
+
+    # Push CS.
+    rdsel t4, cs, dataSize=8
+    st t4, ss, [1, t0, rsp], "-env.dataSize", addressSize=ssz
+    # Push RIP.
+    rdip t7
+    st t7, ss, [1, t0, rsp], "-env.dataSize * 2", addressSize=ssz
+    subi rsp, rsp, "env.dataSize * 2", dataSize=ssz
+
+    # Install the new selector, base and RIP values.
+    wrsel cs, t2, dataSize=2
+    wrbase cs, t3, dataSize=8
+    wrip t1, t0
+};
+
+def macroop CALL_FAR_REAL_M {
+    .function_call
+    .control_indirect
+
+    lea t1, seg, sib, disp, dataSize=asz
+    # Load the selector.
+    ld t2, seg, [1, t0, t1], dsz, dataSize=2
+    # Load the offset.
+    ld t1, seg, [1, t0, t1]
+
+    # Compute the base.
+    zexti t3, t2, 15, dataSize=8
+    slli t3, t3, 4, dataSize=8
+
+    # Make sure pushing the RIP will work after we push cs.
+    cda ss, [1, t0, rsp], "-env.dataSize * 2", addressSize=ssz
+
+    # Push CS.
+    rdsel t4, cs, dataSize=8
+    st t4, ss, [1, t0, rsp], "-env.dataSize", addressSize=ssz
+    # Push RIP.
+    rdip t7
+    st t7, ss, [1, t0, rsp], "-env.dataSize * 2", addressSize=ssz
+    subi rsp, rsp, "env.dataSize * 2", dataSize=ssz
+
+    # Install the new selector, base and RIP values.
+    wrsel cs, t2, dataSize=2
+    wrbase cs, t3, dataSize=8
+    wrip t1, t0
+};
+
+def macroop CALL_FAR_REAL_P {
+    panic "Far call in real mode doesn't support RIP addressing."
+};
 '''
 #let {{
 #    class CALL(Inst):