Toolchain+Meta: Support kernel debugging with host AArch64 GDB

Previously, we would unconditionally build GDB from source for the
AArch64 toolchain. This commit makes it possible to use the system's
`gdb` binary if it supports the architecture, or `aarch64-elf-gdb` if
such a package is installed.

An `aarch64-elf-gdb` package will be available through Homebrew once
this PR is merged: Homebrew/homebrew-core#127323

Meta/debug-kernel.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 SCRIPT_DIR="$(dirname "${0}")"
 
@@ -9,16 +9,18 @@ fi
 # Set this environment variable to override the default debugger.
 #
 if [ -z "$SERENITY_KERNEL_DEBUGGER" ]; then
- if [ "$SERENITY_ARCH" = "aarch64" ]; then
- # Prepend the toolchain aarch64 bin directory so we pick up GDB from there
- PATH="$SCRIPT_DIR/../Toolchain/Local/aarch64/bin:$PATH"
- SERENITY_KERNEL_DEBUGGER="aarch64-pc-serenity-gdb"
+ # Prepend the toolchain bin directory so we pick up GDB from there
+ PATH="$SCRIPT_DIR/../Toolchain/Local/$SERENITY_ARCH/bin:$PATH"
+
+ if command -v "$SERENITY_ARCH-pc-serenity-gdb" >/dev/null; then
+ SERENITY_KERNEL_DEBUGGER="$SERENITY_ARCH-pc-serenity-gdb"
+ elif command -v "$SERENITY_ARCH-elf-gdb" >/dev/null; then
+ SERENITY_KERNEL_DEBUGGER="$SERENITY_ARCH-elf-gdb"
+ elif command -v gdb >/dev/null && gdb ex 'set architecture' -ex 'quit' | grep "${SERENITY_ARCH//_/-}"; then
+ SERENITY_KERNEL_DEBUGGER="gdb"
  else
- if command -v x86_64-elf-gdb >/dev/null 2>&1; then
- SERENITY_KERNEL_DEBUGGER="x86_64-elf-gdb"
- else
- SERENITY_KERNEL_DEBUGGER=gdb
- fi
+ echo "Error: No suitable GDB installation found." >&2
+ exit 1
  fi
 fi
 

Toolchain/BuildIt.sh

@@ -100,6 +100,21 @@ buildstep() {
  "$@" 2>&1 | sed $'s|^|\x1b[34m['"${NAME}"$']\x1b[39m |'
 }
 
+has_gdb() {
+ ARCH=$1
+ ARCH_DASH="${ARCH//_/-}"
+ if command -v gdb >/dev/null && gdb -ex 'set architecture' -ex 'quit' | grep "$ARCH_DASH"; then
+ return 0
+ else
+ command -v "$ARCH"-elf-gdb >/dev/null
+ fi
+}
+
+NEEDS_GDB=1
+if has_gdb "$ARCH"; then
+ NEEDS_GDB=0
+fi
+
 # === DEPENDENCIES ===
 buildstep dependencies echo "Checking whether 'make' is available..."
 if ! command -v ${MAKE:-make} >/dev/null; then
@@ -182,8 +197,9 @@ popd
 # === DOWNLOAD AND PATCH ===
 
 pushd "$DIR/Tarballs"
- # Build aarch64-gdb for cross-debugging support on x86 systems
- if [ "$ARCH" = "aarch64" ]; then
+ # Build gdb for cross-debugging support
+ if [ $NEEDS_GDB -eq 1 ]; then
+ echo "GDB not found for $ARCH. Will build it from source."
  md5=""
  if [ -e "$GDB_PKG" ]; then
  md5="$($MD5SUM $GDB_PKG | cut -f1 -d' ')"
@@ -221,7 +237,7 @@ pushd "$DIR/Tarballs"
  echo "Skipped downloading gcc"
  fi
 
- if [ "$ARCH" = "aarch64" ]; then
+ if [ $NEEDS_GDB -eq 1 ]; then
  if [ -d ${GDB_NAME} ]; then
  rm -rf "${GDB_NAME}"
  rm -rf "$DIR/Build/$ARCH/$GDB_NAME"
@@ -319,7 +335,7 @@ mkdir -p "$DIR/Build/$ARCH"
 pushd "$DIR/Build/$ARCH"
  unset PKG_CONFIG_LIBDIR # Just in case
 
- if [ "$ARCH" = "aarch64" ]; then
+ if [ $NEEDS_GDB -eq 1 ]; then
  rm -rf gdb
  mkdir -p gdb