From a5d89ca5dfa39312862928b542819f05fc40df91 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 4 Feb 2021 22:53:33 +0100
Subject: [PATCH] SymbolServer+bt: Symbolicate kernel addresses if /boot/Kernel
 available

The /boot directory is only accessible to root by default, but anyone
wanting access to kernel symbols for development can get them by making
/boot/Kernel accessible to the "symbol" user.
---
 Userland/Services/SymbolServer/main.cpp |  8 ++++++++
 Userland/Utilities/bt.cpp               | 13 +++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/Userland/Services/SymbolServer/main.cpp b/Userland/Services/SymbolServer/main.cpp
index 8d6e1a2f45..f975f3b37b 100644
--- a/Userland/Services/SymbolServer/main.cpp
+++ b/Userland/Services/SymbolServer/main.cpp
@@ -49,6 +49,14 @@ int main(int, char**)
         return 1;
     }
 
+    // NOTE: Developers can opt into kernel symbolication by making /boot/Kernel accessible to the "symbol" user.
+    if (access("/boot/Kernel", F_OK) == 0) {
+        if (unveil("/boot/Kernel", "r") < 0) {
+            perror("unveil");
+            return 1;
+        }
+    }
+
     if (unveil(nullptr, nullptr) < 0) {
         perror("unveil");
         return 1;
diff --git a/Userland/Utilities/bt.cpp b/Userland/Utilities/bt.cpp
index ba0e906cff..55fbbd6921 100644
--- a/Userland/Utilities/bt.cpp
+++ b/Userland/Utilities/bt.cpp
@@ -70,11 +70,18 @@ int main(int argc, char** argv)
         FlatPtr base { 0 };
         size_t size { 0 };
         String path;
+        bool is_relative { true };
     };
 
     Vector<FlatPtr> stack;
     Vector<RegionWithSymbols> regions;
 
+    regions.append(RegionWithSymbols {
+        .base = 0xc0000000,
+        .size = 0x3fffffff,
+        .path = "/boot/Kernel",
+        .is_relative = false });
+
     {
         // FIXME: Support multiple threads in the same process!
         auto stack_path = String::formatted("/proc/{}/stacks/{}", pid, pid);
@@ -141,7 +148,6 @@ int main(int argc, char** argv)
     auto client = SymbolClient::Client::construct();
 
     for (auto address : stack) {
-
         const RegionWithSymbols* found_region = nullptr;
         for (auto& region : regions) {
             if (address >= region.base && address < (region.base + region.size)) {
@@ -156,7 +162,10 @@ int main(int argc, char** argv)
         }
 
         Vector<FlatPtr> addresses;
-        addresses.append(address - found_region->base);
+        if (found_region->is_relative)
+            addresses.append(address - found_region->base);
+        else
+            addresses.append(address);
 
         auto symbols = client->symbolicate(found_region->path, addresses);
         if (symbols.is_empty()) {