[lldb][RISCV] add jitted function calls to ABI

Function calls support in LLDB expressions for RISCV: 1 of 6

Augments corresponding functionality to RISCV ABI, which allows to jit
lldb expressions and thus make function calls inside them. Only function
calls with integer and void function arguments and return value are
supported.

Author: dlav-sc

lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.cpp

@@ -10,7 +10,9 @@
 
 #include <array>
 #include <limits>
+#include <sstream>
 
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/IR/DerivedTypes.h"
 
 #include "Utility/RISCV_DWARF_Registers.h"
@@ -20,6 +22,7 @@
 #include "lldb/Target/RegisterContext.h"
 #include "lldb/Target/StackFrame.h"
 #include "lldb/Target/Thread.h"
+#include "lldb/Utility/LLDBLog.h"
 #include "lldb/Utility/RegisterValue.h"
 
 #define DEFINE_REG_NAME(reg_num) ConstString(#reg_num).GetCString()
@@ -164,11 +167,83 @@ TotalArgsSizeInWords(bool is_rv64,
   return total_size;
 }
 
+static bool UpdateRegister(RegisterContext *reg_ctx,
+                           const lldb::RegisterKind reg_kind,
+                           const uint32_t reg_num, const addr_t value) {
+  Log *log = GetLog(LLDBLog::Expressions);
+
+  const RegisterInfo *reg_info = reg_ctx->GetRegisterInfo(reg_kind, reg_num);
+
+  LLDB_LOG(log, "Writing %s: 0x%" PRIx64, reg_info->name,
+           static_cast<uint64_t>(value));
+  if (!reg_ctx->WriteRegisterFromUnsigned(reg_info, value)) {
+    LLDB_LOG(log, "Writing %s: failed", reg_info->name);
+    return false;
+  }
+  return true;
+}
+
+static void LogInitInfo(Log *log, const Thread &thread, addr_t sp,
+                        addr_t func_addr, addr_t return_addr,
+                        const llvm::ArrayRef<addr_t> args) {
+  assert(log);
+  std::stringstream ss;
+  ss << "ABISysV_riscv::PrepareTrivialCall"
+     << " (tid = 0x%" << std::hex << thread.GetID() << ", sp = 0x%" << sp
+     << ", func_addr = 0x%" << func_addr << ", return_addr = 0x%"
+     << return_addr;
+
+  for (auto &&[idx, arg] : enumerate(args))
+    ss << ", arg" << std::dec << idx << " = 0x%" << std::hex << arg;
+  ss << ")";
+  log->PutString(ss.str());
+}
+
 bool ABISysV_riscv::PrepareTrivialCall(Thread &thread, addr_t sp,
                                        addr_t func_addr, addr_t return_addr,
                                        llvm::ArrayRef<addr_t> args) const {
-  // TODO: Implement
-  return false;
+  Log *log = GetLog(LLDBLog::Expressions);
+  if (log)
+    LogInitInfo(log, thread, sp, func_addr, return_addr, args);
+
+  const auto reg_ctx_sp = thread.GetRegisterContext();
+  if (!reg_ctx_sp) {
+    LLDB_LOG(log, "Failed to get RegisterContext");
+    return false;
+  }
+
+  if (args.size() > s_regs_for_args_count) {
+    LLDB_LOG(log, "Function has %lu arguments, but only %lu are allowed!",
+             args.size(), s_regs_for_args_count);
+    return false;
+  }
+
+  // Write arguments to registers
+  for (auto &&[idx, arg] : enumerate(args)) {
+    const RegisterInfo *reg_info = reg_ctx_sp->GetRegisterInfo(
+        eRegisterKindGeneric, LLDB_REGNUM_GENERIC_ARG1 + idx);
+    LLDB_LOG(log, "About to write arg%lu (0x%" PRIx64 ") into %s", idx, arg,
+             reg_info->name);
+
+    if (!reg_ctx_sp->WriteRegisterFromUnsigned(reg_info, arg)) {
+      LLDB_LOG(log, "Failed to write arg%lu (0x%" PRIx64 ") into %s", idx, arg,
+               reg_info->name);
+      return false;
+    }
+  }
+
+  if (!UpdateRegister(reg_ctx_sp.get(), eRegisterKindGeneric,
+                      LLDB_REGNUM_GENERIC_PC, func_addr))
+    return false;
+  if (!UpdateRegister(reg_ctx_sp.get(), eRegisterKindGeneric,
+                      LLDB_REGNUM_GENERIC_SP, sp))
+    return false;
+  if (!UpdateRegister(reg_ctx_sp.get(), eRegisterKindGeneric,
+                      LLDB_REGNUM_GENERIC_RA, return_addr))
+    return false;
+
+  LLDB_LOG(log, "ABISysV_riscv::%s: success", __func__);
+  return true;
 }
 
 bool ABISysV_riscv::PrepareTrivialCall(
@@ -222,14 +297,14 @@ bool ABISysV_riscv::PrepareTrivialCall(
   assert(prototype.getFunctionNumParams() == args.size());
 
   const size_t num_args = args.size();
-  const size_t regs_for_args_count = 8U;
   const size_t num_args_in_regs =
-      num_args > regs_for_args_count ?  regs_for_args_count : num_args;
+      num_args > s_regs_for_args_count ? s_regs_for_args_count : num_args;
 
   // Number of arguments passed on stack.
   size_t args_size = TotalArgsSizeInWords(m_is_rv64, args);
-  auto on_stack =
-      args_size <= regs_for_args_count ? 0 : args_size - regs_for_args_count;
+  auto on_stack = args_size <= s_regs_for_args_count
+                      ? 0
+                      : args_size - s_regs_for_args_count;
   auto offset = on_stack * word_size;
 
   uint8_t reg_value[8];
@@ -260,7 +335,7 @@ bool ABISysV_riscv::PrepareTrivialCall(
       ++reg_index;
     }
 
-    if (reg_index < regs_for_args_count || size == 0)
+    if (reg_index < s_regs_for_args_count || size == 0)
       continue;
 
     // Remaining arguments are passed on the stack.

lldb/source/Plugins/ABI/RISCV/ABISysV_riscv.h

@@ -124,6 +124,9 @@ class ABISysV_riscv : public lldb_private::RegInfoBasedABI {
   using lldb_private::RegInfoBasedABI::RegInfoBasedABI; // Call CreateInstance
                                                         // instead.
   bool m_is_rv64; // true if target is riscv64; false if target is riscv32
+  static constexpr size_t s_regs_for_args_count =
+      8U; // number of argument registers (the base integer calling convention
+          // provides 8 argument registers, a0-a7)
 };
 
 #endif // liblldb_ABISysV_riscv_h_