Kernel: Load executables on demand when symbolicating

Previously we would map the entire executable of a program in its own
address space (but make it unavailable to userspace code.)

This patch removes that and changes the symbolication code to remap
the executable on demand (and into the kernel's own address space
instead of the process address space.)

This opens up a couple of further simplifications that will follow.

Kernel/KSyms.cpp

@@ -127,6 +127,11 @@ static void load_ksyms_from_data(const ByteBuffer& buffer)
         hang();
         return;
     }
+
+    OwnPtr<Process::ELFBundle> elf_bundle;
+    if (Process::current)
+        elf_bundle = Process::current->elf_bundle();
+
     struct RecognizedSymbol {
         u32 address;
         const KSym* ksym;
@@ -154,8 +159,8 @@ static void load_ksyms_from_data(const ByteBuffer& buffer)
         if (!symbol.address)
             break;
         if (!symbol.ksym) {
-            if (Process::current && Process::current->elf_loader() && Process::current->elf_loader()->has_symbols()) {
-                dbg() << String::format("%p", symbol.address) << "  " << Process::current->elf_loader()->symbolicate(symbol.address);
+            if (elf_bundle && elf_bundle->elf_loader->has_symbols()) {
+                dbg() << String::format("%p", symbol.address) << "  " << elf_bundle->elf_loader->symbolicate(symbol.address);
             } else {
                 dbg() << String::format("%p", symbol.address) << " (no ELF symbols for process)";
             }

Kernel/Process.cpp

@@ -947,7 +947,6 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
 #endif
     }
 
-    m_elf_loader = move(loader);
     m_executable = main_program_description->custody();
 
     m_promises = m_execpromises;
@@ -1516,8 +1515,8 @@ void Process::crash(int signal, u32 eip)
     if (eip >= 0xc0000000 && ksyms_ready) {
         auto* ksym = ksymbolicate(eip);
         dbg() << "\033[31;1m" << String::format("%p", eip) << "  " << (ksym ? demangle(ksym->name) : "(k?)") << " +" << (ksym ? eip - ksym->address : 0) << "\033[0m\n";
-    } else if (m_elf_loader) {
-        dbg() << "\033[31;1m" << String::format("%p", eip) << "  " << m_elf_loader->symbolicate(eip) << "\033[0m\n";
+    } else if (auto elf_bundle = this->elf_bundle()) {
+        dbg() << "\033[31;1m" << String::format("%p", eip) << "  " << elf_bundle->elf_loader->symbolicate(eip) << "\033[0m\n";
     } else {
         dbg() << "\033[31;1m" << String::format("%p", eip) << "  (?)\033[0m\n";
     }
@@ -3051,7 +3050,6 @@ void Process::finalize()
     m_cwd = nullptr;
     m_root_directory = nullptr;
     m_root_directory_relative_to_global_root = nullptr;
-    m_elf_loader = nullptr;
 
     disown_all_shared_buffers();
     {
@@ -4815,4 +4813,18 @@ void Process::set_tty(TTY* tty)
     m_tty = tty;
 }
 
+OwnPtr<Process::ELFBundle> Process::elf_bundle() const
+{
+    if (!m_executable)
+        return nullptr;
+    auto bundle = make<ELFBundle>();
+    ASSERT(m_executable->inode().shared_vmobject());
+    auto& vmobject = *m_executable->inode().shared_vmobject();
+    bundle->region = MM.allocate_kernel_region_with_vmobject(const_cast<SharedInodeVMObject&>(vmobject), vmobject.size(), "ELF bundle", Region::Access::Read);
+    if (!bundle->region)
+        return nullptr;
+    bundle->elf_loader = make<ELFLoader>(bundle->region->vaddr().as_ptr(), bundle->region->size());
+    return bundle;
+}
+
 }

Kernel/Process.h

@@ -386,7 +386,11 @@ public:
 
     Lock& big_lock() { return m_big_lock; }
 
-    const ELFLoader* elf_loader() const { return m_elf_loader.ptr(); }
+    struct ELFBundle {
+        OwnPtr<Region> region;
+        OwnPtr<ELFLoader> elf_loader;
+    };
+    OwnPtr<ELFBundle> elf_bundle() const;
 
     int icon_id() const { return m_icon_id; }
 
@@ -495,7 +499,6 @@ private:
     FixedArray<gid_t> m_extra_gids;
 
     RefPtr<ProcessTracer> m_tracer;
-    OwnPtr<ELFLoader> m_elf_loader;
 
     WeakPtr<Region> m_master_tls_region;
     size_t m_master_tls_size { 0 };

Kernel/Thread.cpp

@@ -754,7 +754,7 @@ struct RecognizedSymbol {
     const KSym* ksym;
 };
 
-static bool symbolicate(const RecognizedSymbol& symbol, const Process& process, StringBuilder& builder)
+static bool symbolicate(const RecognizedSymbol& symbol, const Process& process, StringBuilder& builder, Process::ELFBundle* elf_bundle)
 {
     if (!symbol.address)
         return false;
@@ -764,8 +764,8 @@ static bool symbolicate(const RecognizedSymbol& symbol, const Process& process,
         if (!is_user_address(VirtualAddress(symbol.address))) {
             builder.append("0xdeadc0de\n");
         } else {
-            if (!Scheduler::is_active() && process.elf_loader() && process.elf_loader()->has_symbols())
-                builder.appendf("%p  %s\n", symbol.address, process.elf_loader()->symbolicate(symbol.address).characters());
+            if (!Scheduler::is_active() && elf_bundle && elf_bundle->elf_loader->has_symbols())
+                builder.appendf("%p  %s\n", symbol.address, elf_bundle->elf_loader->symbolicate(symbol.address).characters());
             else
                 builder.appendf("%p\n", symbol.address);
         }
@@ -794,6 +794,7 @@ String Thread::backtrace_impl() const
     }
 
     auto& process = const_cast<Process&>(this->process());
+    auto elf_bundle = process.elf_bundle();
     ProcessPagingScope paging_scope(process);
 
     uintptr_t stack_ptr = start_frame;
@@ -815,7 +816,7 @@ String Thread::backtrace_impl() const
 
     StringBuilder builder;
     for (auto& symbol : recognized_symbols) {
-        if (!symbolicate(symbol, process, builder))
+        if (!symbolicate(symbol, process, builder, elf_bundle.ptr()))
             break;
     }
     return builder.to_string();