Emulator: Use libc.so bounds to fast-reject non-malloc addresses

The auditing code always starts by checking if we're in one of the
ignored code ranges (malloc, free, realloc, syscall, etc.)

To reduce the number of checks needed, we can cache the bounds of
the LibC text segment. This allows us to fast-reject addresses that
cannot possibly be a LibC function.

Userland/DevTools/UserspaceEmulator/Emulator.cpp

@@ -1054,6 +1054,8 @@ u32 Emulator::virt$mmap(u32 params_addr)
     } else {
         auto region = MmapRegion::create_file_backed(final_address, final_size, params.prot, params.flags, params.fd, params.offset, move(name_str));
         if (region->name() == "libc.so: .text") {
+            m_libc_start = final_address;
+            m_libc_end = final_address + final_size;
             bool rc = find_malloc_symbols(*region);
             VERIFY(rc);
         }

Userland/DevTools/UserspaceEmulator/Emulator.h

@@ -65,6 +65,7 @@ public:
     bool is_in_malloc_or_free() const;
     bool is_in_loader_code() const;
     bool is_in_libsystem() const;
+    bool is_in_libc() const;
 
     void did_receive_signal(int signum) { m_pending_signals |= (1 << signum); }
 
@@ -199,6 +200,8 @@ private:
     FlatPtr m_malloc_size_symbol_start { 0 };
     FlatPtr m_malloc_size_symbol_end { 0 };
 
+    FlatPtr m_libc_start { 0 };
+    FlatPtr m_libc_end { 0 };
     FlatPtr m_libsystem_start { 0 };
     FlatPtr m_libsystem_end { 0 };
 
@@ -226,6 +229,11 @@ private:
     RangeAllocator m_range_allocator;
 };
 
+ALWAYS_INLINE bool Emulator::is_in_libc() const
+{
+    return m_cpu.base_eip() >= m_libc_start && m_cpu.base_eip() < m_libc_end;
+}
+
 ALWAYS_INLINE bool Emulator::is_in_libsystem() const
 {
     return m_cpu.base_eip() >= m_libsystem_start && m_cpu.base_eip() < m_libsystem_end;
@@ -233,6 +241,8 @@ ALWAYS_INLINE bool Emulator::is_in_libsystem() const
 
 ALWAYS_INLINE bool Emulator::is_in_malloc_or_free() const
 {
+    if (!is_in_libc())
+        return false;
     return (m_cpu.base_eip() >= m_malloc_symbol_start && m_cpu.base_eip() < m_malloc_symbol_end)
         || (m_cpu.base_eip() >= m_free_symbol_start && m_cpu.base_eip() < m_free_symbol_end)
         || (m_cpu.base_eip() >= m_realloc_symbol_start && m_cpu.base_eip() < m_realloc_symbol_end)