[llvm] [llvm-exegesis] [AArch64] Add support for Load Instructions in subprocess execution mode (PR #144895)

[Sjoerd Meijer via llvm-commits]

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@@ -155,6 +286,156 @@ class ExegesisAArch64Target : public ExegesisTarget {
 
 } // namespace
 
+#ifdef __linux__
+// true : let use of fixed address to Virtual Address Space Ceiling
+// false: let kernel choose the address of the auxiliary memory
+bool UseFixedAddress = true;
+
+static constexpr const uintptr_t VAddressSpaceCeiling = 0x0000800000000000;
+
+static void generateRoundToNearestPage(unsigned int TargetRegister,
+                                       std::vector<MCInst> &GeneratedCode) {
+  int PageSizeShift = static_cast<int>(round(log2(getpagesize())));
+  // Round down to the nearest page by getting rid of the least significant bits
+  // representing location in the page.
+
+  // Single instruction using AND with inverted mask (effectively BIC)
+  uint64_t BitsToClearMask = (1ULL << PageSizeShift) - 1; // 0xFFF
+  uint64_t AndMask = ~BitsToClearMask;                    // ...FFFFFFFFFFFF000
+  GeneratedCode.push_back(MCInstBuilder(AArch64::ANDXri)
+                              .addReg(TargetRegister) // Xd
+                              .addReg(TargetRegister) // Xn
+                              .addImm(AndMask)        // imm bitmask
+  );
+}
+
+std::vector<MCInst>
+ExegesisAArch64Target::generateExitSyscall(unsigned ExitCode) const {
+  std::vector<MCInst> ExitCallCode;
+  ExitCallCode.push_back(loadImmediate(AArch64::X0, 64, APInt(64, ExitCode)));
+  generateSysCall(SYS_exit, ExitCallCode); // SYS_exit is 93
+  return ExitCallCode;
+}
+
+std::vector<MCInst>
+ExegesisAArch64Target::generateMmap(uintptr_t Address, size_t Length,
+                                    uintptr_t FileDescriptorAddress) const {
+  // mmap(address, length, prot, flags, fd, offset=0)
+  int flags = MAP_SHARED;
+  if (Address != 0) {
+    flags |= MAP_FIXED_NOREPLACE;
+  }
+  std::vector<MCInst> MmapCode;
+  MmapCode.push_back(
+      loadImmediate(AArch64::X0, 64, APInt(64, Address))); // map adr
+  MmapCode.push_back(
+      loadImmediate(AArch64::X1, 64, APInt(64, Length))); // length
+  MmapCode.push_back(loadImmediate(AArch64::X2, 64,
+                                   APInt(64, PROT_READ | PROT_WRITE))); // prot
+  MmapCode.push_back(loadImmediate(AArch64::X3, 64, APInt(64, flags))); // flags
+  // FIXME: File descriptor address is not initialized.
+  // Copy file descriptor location from aux memory into X4
+  MmapCode.push_back(
+      loadImmediate(AArch64::X4, 64, APInt(64, FileDescriptorAddress))); // fd
+  // Dereference file descriptor into FD argument register
+  // MmapCode.push_back(MCInstBuilder(AArch64::LDRWui)
+  //                        .addReg(AArch64::W4)   // Destination register
+  //                        .addReg(AArch64::X4)   // Base register (address)
+  //                        .addImm(0));           // Offset (-byte words)
+  // FIXME: This is not correct.
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sjoerdmeijer wrote:

What does this refer to? The previous commented out code, or the next line? 
And what does this mean that this is not correct, what is the consequence?

https://github.com/llvm/llvm-project/pull/144895