bjit: allocate code block using mmap

also add a option to pass MAP_32BIT to mmap

src/codegen/baseline_jit.cpp

@@ -16,6 +16,7 @@
 
 #include <llvm/ADT/DenseMap.h>
 #include <llvm/ADT/DenseSet.h>
+#include <sys/mman.h>
 
 #include "codegen/irgen/hooks.h"
 #include "codegen/memmgr.h"
@@ -59,12 +60,22 @@ static_assert(JitCodeBlock::scratch_size == 256, "have to update EH table!");
 
 constexpr int code_size = JitCodeBlock::memory_size - sizeof(eh_info);
 
+JitCodeBlock::MemoryManager::MemoryManager() {
+    int protection = PROT_READ | PROT_WRITE | PROT_EXEC;
+    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+#if ENABLE_BASELINEJIT_MAP_32BIT
+    flags |= MAP_32BIT;
+#endif
+    addr = (uint8_t*)mmap(NULL, JitCodeBlock::memory_size, protection, flags, -1, 0);
+}
+
+JitCodeBlock::MemoryManager::~MemoryManager() {
+    munmap(addr, JitCodeBlock::memory_size);
+    addr = NULL;
+}
+
 JitCodeBlock::JitCodeBlock(llvm::StringRef name)
-    : memory(new uint8_t[memory_size]),
-      entry_offset(0),
-      a(memory.get() + sizeof(eh_info), code_size),
-      is_currently_writing(false),
-      asm_failed(false) {
+    : entry_offset(0), a(memory.get() + sizeof(eh_info), code_size), is_currently_writing(false), asm_failed(false) {
     static StatCounter num_jit_code_blocks("num_baselinejit_code_blocks");
     num_jit_code_blocks.log();
     static StatCounter num_jit_total_bytes("num_baselinejit_total_bytes");

src/codegen/baseline_jit.h

@@ -23,6 +23,9 @@
 
 namespace pyston {
 
+// passes MAP_32BIT to mmap when allocating the memory for the bjit code.
+// it's nice for inspecting the generated asm because the debugger is able to show the name of called C/C++ functions
+#define ENABLE_BASELINEJIT_MAP_32BIT 0
 #define ENABLE_BASELINEJIT_ICS 1
 
 class AST_stmt;
@@ -147,8 +150,18 @@ public:
     static constexpr int sp_adjustment = scratch_size + num_stack_args * 8 + 8 /* = alignment */;
 
 private:
+    struct MemoryManager {
+    private:
+        uint8_t* addr;
+
+    public:
+        MemoryManager();
+        ~MemoryManager();
+        uint8_t* get() { return addr; }
+    };
+
     // the memory block contains the EH frame directly followed by the generated machine code.
-    std::unique_ptr<uint8_t[]> memory;
+    MemoryManager memory;
     int entry_offset;
     assembler::Assembler a;
     bool is_currently_writing;