[X86][MC] no error diagnostic for out-of-range jrcxz/jecxz/jcxz

[avl]

Summary

This is the fix for PR24072:

X86 instructions jrcxz/jecxz/jcxz performs short jumps if rcx/ecx/cx register is 0
The maximum relative offset for a forward short jump is 127 Bytes (0x7F).
The maximum relative offset for a backward short jump is 128 Bytes (0x80).

Gnu assembler warns when the distance of the jump exceeds the maximum but llvm-as does not.

The fix for that problem was already presented for review : D36991
The llvm codebase changed since August of 2017, thus it does not pass
current check-all testing. I limited it for only PCRel fixups and to
not check not-resolved symbols.

[craig.topper]

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

122

I think the && should be at the end of the previous line. Can you run this through clang-format?

[avl]

addressed comment. applied clang-format. Thanks!

[craig.topper]

LGTM

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

 //===-- X86AsmBackend.cpp - X86 Assembler Backend -------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "MCTargetDesc/X86BaseInfo.h"
 #include "MCTargetDesc/X86FixupKinds.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/MC/MCAsmBackend.h"
+#include "llvm/MC/MCAssembler.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCMachObjectWriter.h"
 #include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 static unsigned getFixupKindSize(unsigned Kind) {
   switch (Kind) {
   default:
     llvm_unreachable("invalid fixup kind!");
public:
   void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                   const MCValue &Target, MutableArrayRef<char> Data,
                   uint64_t Value, bool IsResolved,
                   const MCSubtargetInfo *STI) const override {
     unsigned Size = getFixupKindSize(Fixup.getKind());
 
     assert(Fixup.getOffset() + Size <= Data.size() && "Invalid fixup offset!");
 
+    int64_t SignedValue = static_cast<int64_t>(Value);
+    if ((Target.isAbsolute() || IsResolved) &&
+        getFixupKindInfo(Fixup.getKind()).Flags &
+            MCFixupKindInfo::FKF_IsPCRel) {
+      // check that PC relative fixup fits into the fixup size.
+      if (Size > 0 && !isIntN(Size * 8, SignedValue))
+        Asm.getContext().reportError(
+            Fixup.getLoc(), "value of " + Twine(SignedValue) +
+                                " is too large for field of " + Twine(Size) +
+                                ((Size == 1) ? " byte." : " bytes."));
+    } else {
       // Check that uppper bits are either all zeros or all ones.
       // Specifically ignore overflow/underflow as long as the leakage is
       // limited to the lower bits. This is to remain compatible with
       // other assemblers.
-    assert((Size == 0 || isIntN(Size * 8 + 1, Value)) &&
+      assert((Size == 0 || isIntN(Size * 8 + 1, SignedValue)) &&
              "Value does not fit in the Fixup field");
+    }
 
     for (unsigned i = 0; i != Size; ++i)
       Data[Fixup.getOffset() + i] = uint8_t(Value >> (i * 8));
   }
 
   bool mayNeedRelaxation(const MCInst &Inst,
                          const MCSubtargetInfo &STI) const override;
 

llvm/test/MC/MachO/reloc.s

 
 L0:
         .long L0
         .long L1
 
         .text
 _f0:
 L1:
-        jmp 0xbabecafe
+        jmp 0x7abecafe
         jmp L0
         jmp L1
         ret
 
         .objc_class_name_A=0
   .globl .objc_class_name_A
 
         .text

llvm/test/MC/X86/x86-jcxz-loop-fixup.s

+# RUN: not llvm-mc -filetype=obj -triple=x86_64-linux-gnu %s 2>&1 | FileCheck %s
+
+       .balign 128 
+label00:
+// CHECK: value of 253 is too large for field of 1 byte.
+  jecxz   label01
+// CHECK: value of 251 is too large for field of 1 byte.
+  jrcxz   label01
+// CHECK: value of 249 is too large for field of 1 byte.
+  loop  label01
+// CHECK: value of 247 is too large for field of 1 byte. 
+  loope  label01
+// CHECK: value of 245 is too large for field of 1 byte.
+  loopne  label01
+        .balign 256 
+label01:
+// CHECK: value of -259 is too large for field of 1 byte.
+  jecxz   label00
+// CHECK: value of -261 is too large for field of 1 byte.
+  jrcxz   label00
+// CHECK: value of -263 is too large for field of 1 byte.
+  loop  label00
+// CHECK: value of -265 is too large for field of 1 byte.
+  loope  label00
+// CHECK: value of -267 is too large for field of 1 byte.
+  loopne  label00