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

[Lakshay Kumar 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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lakshayk-nv wrote:

> // Dereference file descriptor into FD argument register
I added this in attempt to closely follow x86 implementation. Not sure, If this is some arch specific quirk for x86 or arch independently requirement. (I was unable to understand its utility, maybe @boomanaiden154  can expand on this) 
Referred 4fa3e93e68df41465b7accf6be9c57f06b877dac.

I will be removing above mentioned lines

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