From a79d8d8ae54a1a1dc971df8c24754f2a52feb142 Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Sat, 27 Jul 2019 12:01:14 +0200
Subject: [PATCH] Kernel: Add (expensive) but valuable userspace symbols to
 stacks.

This is expensive because we have to page in the entire executable for every
process up front for this to work. This is due to the page fault code not
being strong enough to run while another process is active.

Note that we already had userspace symbols in *crash* stacks. This patch
adds them generally, so they show up in /proc, Process Manager, etc.

There's room for improvement here, but the debugging benefits way overshadow
the performance penalty right now. :^)
---
 Kernel/Makefile    | 1 +
 Kernel/Process.cpp | 5 +++++
 Kernel/Thread.cpp  | 8 +++++++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Kernel/Makefile b/Kernel/Makefile
index 62f8b1276b..c302147db7 100644
--- a/Kernel/Makefile
+++ b/Kernel/Makefile
@@ -105,6 +105,7 @@ CXXFLAGS += -nostdlib -nostdinc -nostdinc++
 CXXFLAGS += -I../Toolchain/Local/i686-pc-serenity/include/c++/8.3.0/
 CXXFLAGS += -I../Toolchain/Local/i686-pc-serenity/include/c++/8.3.0/i686-pc-serenity/
 DEFINES += -DKERNEL
+DEFINES += -DEXPENSIVE_USERSPACE_STACKS
 LDFLAGS += -Ttext 0x10000 -Wl,-T linker.ld -nostdlib
 
 all: $(KERNEL) kernel.map
diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 3e65b7b0b3..34439560eb 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -350,6 +350,11 @@ int Process::do_exec(String path, Vector<String> arguments, Vector<String> envir
         bool success = region->page_in();
         ASSERT(success);
     }
+
+#ifdef EXPENSIVE_USERSPACE_STACKS
+    region->page_in();
+#endif
+
     OwnPtr<ELFLoader> loader;
     {
         // Okay, here comes the sleight of hand, pay close attention..
diff --git a/Kernel/Thread.cpp b/Kernel/Thread.cpp
index 71194807c1..e2370135e0 100644
--- a/Kernel/Thread.cpp
+++ b/Kernel/Thread.cpp
@@ -1,3 +1,4 @@
+#include <AK/ELF/ELFLoader.h>
 #include <AK/StringBuilder.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/Process.h>
@@ -570,7 +571,12 @@ String Thread::backtrace(ProcessInspectionHandle&) const
         if (!symbol.address)
             break;
         if (!symbol.ksym) {
-            builder.appendf("%p\n", symbol.address);
+#ifdef EXPENSIVE_USERSPACE_STACKS
+            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());
+            else
+#endif
+                builder.appendf("%p\n", symbol.address);
             continue;
         }
         unsigned offset = symbol.address - symbol.ksym->address;