[BOLT] Ignore functions accessing false positive jump tables

Disassembly and branch target analysis are not decoupled, so any
analysis that depends on disassembly may not operate properly.

In specific, analyzeJumpTable uses instruction bounds check property.
A jump table was analyzed twice: (a) during disassembly, and (b) after
disassembly, so there are potentially some mismatched results.

In this update, functions that access JTs which fail the second check
will be marked as ignored.

Test Plan:
```
ninja check-bolt
```

Reviewed By: Amir

Differential Revision: https://reviews.llvm.org/D130431

Author: nhuhuan

bolt/lib/Core/BinaryContext.cpp

@@ -622,6 +622,10 @@ bool BinaryContext::analyzeJumpTable(
 void BinaryContext::populateJumpTables() {
   LLVM_DEBUG(dbgs() << "DataPCRelocations: " << DataPCRelocations.size()
                     << '\n');
+
+  // Collect jump tables that pass the analyzeJumpTable's first check,
+  // but fail the analyzeJumpTable's second check
+  SmallVector<JumpTable *, 1> AbortedJTs;
   for (auto JTI = JumpTables.begin(), JTE = JumpTables.end(); JTI != JTE;
        ++JTI) {
     JumpTable *JT = JTI->second;
@@ -640,6 +644,13 @@ void BinaryContext::populateJumpTables() {
     const bool Success =
         analyzeJumpTable(JT->getAddress(), JT->Type, *(JT->Parents[0]),
                          NextJTAddress, &JT->EntriesAsAddress);
+    // !Success means a false positive from earlier analysis run due to
+    // different context. A possible culprit is instruction bounds check.
+    // Previous run happens during disassembly. If the target function
+    // is not disassembled, the check will be skipped, leading to a false
+    // positive
+    //
+    // Solution: Ignore fragments accessing JT that fails the check
     if (!Success) {
       LLVM_DEBUG(ListSeparator LS;
                  dbgs() << "failed to analyze jump table in function ";
@@ -659,7 +670,8 @@ void BinaryContext::populateJumpTables() {
                    dbgs() << "\n";);
         NextJTI->second->print(dbgs());
       }
-      llvm_unreachable("jump table heuristic failure");
+      AbortedJTs.push_back(JT);
+      continue;
     }
     for (BinaryFunction *Frag : JT->Parents) {
       for (uint64_t EntryAddress : JT->EntriesAsAddress)
@@ -689,6 +701,15 @@ void BinaryContext::populateJumpTables() {
         addFragmentsToSkip(Frag);
   }
 
+  // Ignore fragments accessing JT that fails analyzeJumpTable check
+  for (JumpTable *JT : AbortedJTs) {
+    for (BinaryFunction *Frag : JT->Parents) {
+      Frag->setIgnored();
+      Frag->JumpTables.erase(Frag->JumpTables.find(JT->getAddress()));
+    }
+    JumpTables.erase(JumpTables.find(JT->getAddress()));
+  }
+
   if (opts::StrictMode && DataPCRelocations.size()) {
     LLVM_DEBUG({
       dbgs() << DataPCRelocations.size()

bolt/test/X86/fake_jump_table.s

@@ -0,0 +1,49 @@
+# Currently disassembly is not decoupled from branch target analysis.
+# This causes a few checks related to availability of target insn to
+# fail for stripped binaries:
+#   (a) analyzeJumpTable
+#   (b) postProcessEntryPoints
+# This test checks if BOLT can safely support instruction bounds check
+# for cross-function targets.
+
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.out -v=1 -print-cfg
+
+  .text
+  .globl main
+  .type main, %function
+  .p2align 2
+main:
+LBB0:
+  .cfi_startproc
+  andl $0xf, %ecx
+  cmpb $0x4, %cl
+  ja .main.cold.1
+LBB1:
+  leaq FAKE_JUMP_TABLE(%rip), %r8
+  cmpq %r8, %r9
+LBB2:
+  xorq %rax, %rax
+  ret
+  .cfi_endproc
+.size main, .-main
+
+  .globl main.cold.1
+  .type main.cold.1, %function
+  .p2align 2
+main.cold.1:
+  .cfi_startproc
+  nop
+LBB3:
+  callq abort
+  .cfi_endproc
+.size main.cold.1, .-main.cold.1
+
+  .rodata
+  .globl FAKE_JUMP_TABLE
+FAKE_JUMP_TABLE:
+  .long LBB2-FAKE_JUMP_TABLE
+  .long LBB3-FAKE_JUMP_TABLE+0x1