Linux build improvements (#843)

- **Sentry crashpad patch**: Make static libc++ linking conditional on `-stdlib=libc++` being active, so the patch doesn't break gcc or system clang builds that use libstdc++
- **GCC warning fix**: Suppress `-Wunused-but-set-variable` for gcc (false positive with `constinit` static locals passed by reference)
- **ASIO typo fix**: `ASIO_STANDLONE` → `ASIO_STANDALONE`
- **Toolchain verification script**: `scripts/ue_build_linux/verify_linux_toolchains.sh` for testing builds across gcc, ue-clang, clang-19 and clang-20

6 files changed, 146 insertions, 18 deletions

diff --git a/repo/packages/s/sentry-native/patches/0.12.1/crashpad_static_libcxx.patch b/repo/packages/s/sentry-native/patches/0.12.1/crashpad_static_libcxx.patch
index 2005ad4ec..8d0a8f11e 100644
--- a/repo/packages/s/sentry-native/patches/0.12.1/crashpad_static_libcxx.patch
+++ b/repo/packages/s/sentry-native/patches/0.12.1/crashpad_static_libcxx.patch
@@ -1,24 +1,25 @@
 --- a/external/crashpad/handler/CMakeLists.txt	2026-03-09 14:47:42.109197582 +0000
 +++ b/external/crashpad/handler/CMakeLists.txt	2026-03-09 14:51:45.343538268 +0000
-@@ -120,6 +120,21 @@
+@@ -120,6 +120,22 @@
          endif()
      endif()
- 
+
++    # Statically link libc++ and libc++abi into crashpad_handler so it has
++    # no runtime dependency on libc++.so.1. This is needed when building with
++    # a toolchain that uses libc++ (e.g. UE clang) but deploys to systems
++    # where libc++.so.1 is not available.
++    # Only applied when -stdlib=libc++ is active (i.e. not GCC or system clang
++    # using libstdc++).
 +    if(LINUX)
-+        # Statically link libc++ and libc++abi into crashpad_handler so it has
-+        # no runtime dependency on libc++.so.1. This is needed when building with
-+        # a toolchain that uses libc++ (e.g. UE clang) but deploys to systems
-+        # where libc++.so.1 is not available.
-+        # -nostdlib++ suppresses clang's automatic -lc++ addition (a linker flag,
-+        # added at the end). The explicit -Bstatic libs are added via
-+        # target_link_libraries so they appear after crashpad's static archives in
-+        # the link order, letting the single-pass linker resolve all libc++ symbols.
-+        target_link_options(crashpad_handler PRIVATE -nostdlib++)
-+        target_link_libraries(crashpad_handler PRIVATE
-+            -Wl,-Bstatic,-lc++,-lc++abi,-Bdynamic
-+        )
++        string(FIND "${CMAKE_CXX_FLAGS}" "-stdlib=libc++" _libcxx_pos)
++        if(NOT _libcxx_pos EQUAL -1)
++            target_link_options(crashpad_handler PRIVATE -nostdlib++)
++            target_link_libraries(crashpad_handler PRIVATE
++                -Wl,-Bstatic,-lc++,-lc++abi,-Bdynamic
++            )
++        endif()
 +    endif()
 +
      set_property(TARGET crashpad_handler PROPERTY EXPORT_NAME crashpad_handler)
      add_executable(crashpad::handler ALIAS crashpad_handler)
- 
+
diff --git a/repo/packages/s/sentry-native/xmake.lua b/repo/packages/s/sentry-native/xmake.lua
index 43672b9de..0da513ead 100644
--- a/repo/packages/s/sentry-native/xmake.lua
+++ b/repo/packages/s/sentry-native/xmake.lua
@@ -37,7 +37,7 @@ package("sentry-native")
     add_versions("0.4.4", "fe6c711d42861e66e53bfd7ee0b2b226027c64446857f0d1bbb239ca824a3d8d")
     add_patches("0.4.4", path.join(os.scriptdir(), "patches", "0.4.4", "zlib_fix.patch"), "1a6ac711b7824112a9062ec1716a316facce5055498d1f87090d2cad031b865b")
     add_patches("0.7.6", path.join(os.scriptdir(), "patches", "0.7.6", "breakpad_exceptions.patch"), "7781bad0404a92252cbad39e865d17ac663eedade03cbd29c899636c7bfab1b5")
-    add_patches("0.12.1", path.join(os.scriptdir(), "patches", "0.12.1", "crashpad_static_libcxx.patch"), "3c2115b90179808fa639865f6eb23090e2cb6025d816ffb66c2d75c26473ec72")
+    add_patches("0.12.1", path.join(os.scriptdir(), "patches", "0.12.1", "crashpad_static_libcxx.patch"), "e297c1b9dc58f446edfec5566a73c9e3e6b53c207f7247d45b93c640af2bff1a")
     add_patches("0.12.1", path.join(os.scriptdir(), "patches", "0.12.1", "breakpad_exceptions.patch"), "9e0cd152192f87b9ce182c8ddff22c0471acb99bd61a872ca48afbbacdf27575")
 
     add_deps("cmake")
diff --git a/scripts/ue_build_linux/verify_linux_toolchains.sh b/scripts/ue_build_linux/verify_linux_toolchains.sh
new file mode 100755
index 000000000..10fad8a82
--- /dev/null
+++ b/scripts/ue_build_linux/verify_linux_toolchains.sh
@@ -0,0 +1,121 @@
+#!/usr/bin/env bash
+#
+# Verify that the project builds on Linux with gcc, ue-clang, clang-19 and clang-20.
+# Each toolchain gets a clean slate (build dirs + xmake caches wiped).
+#
+# Usage:
+#   ./scripts/verify_linux_toolchains.sh                    # build all four
+#   ./scripts/verify_linux_toolchains.sh gcc clang-19       # build only specific ones
+#   ./scripts/verify_linux_toolchains.sh --clean             # also wipe ~/.xmake package cache
+#
+# Installing toolchains (Ubuntu 24.04):
+#   - gcc: sudo apt install build-essential
+#   - ue-clang: use scripts/ue_build_linux/get_ue_toolchain.sh
+#   - clang-19: sudo apt install clang-19
+#   - clang-20: sudo apt install clang-20
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+PROJECT_DIR="$(cd "$SCRIPT_DIR/../.." && pwd)"
+
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+NC='\033[0m'
+
+PASSED=()
+FAILED=()
+declare -A TIMINGS
+CLEAN_XMAKE_HOME=false
+
+clean_build_state() {
+    echo -e "${YELLOW}Cleaning build state...${NC}"
+    rm -rf "$PROJECT_DIR/.xmake" "$PROJECT_DIR/build"
+    if [ "$CLEAN_XMAKE_HOME" = true ]; then
+        rm -rf ~/.xmake
+    fi
+}
+
+build_toolchain() {
+    local NAME="$1"
+    shift
+    local CONFIG_ARGS=("$@")
+
+    echo ""
+    echo "============================================================"
+    echo -e "${YELLOW}Building with: ${NAME}${NC}"
+    echo "  xmake config args: ${CONFIG_ARGS[*]}"
+    echo "============================================================"
+
+    clean_build_state
+
+    local START_TIME=$SECONDS
+
+    if ! (cd "$PROJECT_DIR" && xmake config -y -m debug "${CONFIG_ARGS[@]}"); then
+        TIMINGS[$NAME]=$(( SECONDS - START_TIME ))
+        echo -e "${RED}FAILED: ${NAME} (config, ${TIMINGS[$NAME]}s)${NC}"
+        FAILED+=("$NAME")
+        return 1
+    fi
+
+    if ! (cd "$PROJECT_DIR" && xmake -y -j"$(nproc)"); then
+        TIMINGS[$NAME]=$(( SECONDS - START_TIME ))
+        echo -e "${RED}FAILED: ${NAME} (build, ${TIMINGS[$NAME]}s)${NC}"
+        FAILED+=("$NAME")
+        return 1
+    fi
+
+    TIMINGS[$NAME]=$(( SECONDS - START_TIME ))
+    echo -e "${GREEN}PASSED: ${NAME} (${TIMINGS[$NAME]}s)${NC}"
+    PASSED+=("$NAME")
+}
+
+# Available toolchain configurations
+declare -A TOOLCHAINS
+TOOLCHAINS[gcc]="--toolchain=gcc"
+TOOLCHAINS[ue-clang]="--toolchain=ue-clang"
+TOOLCHAINS[clang-19]="--toolchain=clang-19"
+TOOLCHAINS[clang-20]="--toolchain=clang-20"
+
+# Parse arguments
+SELECTED=()
+for ARG in "$@"; do
+    if [ "$ARG" = "--clean" ]; then
+        CLEAN_XMAKE_HOME=true
+    else
+        SELECTED+=("$ARG")
+    fi
+done
+
+if [ ${#SELECTED[@]} -eq 0 ]; then
+    SELECTED=(gcc ue-clang clang-19 clang-20)
+fi
+
+TOTAL_START=$SECONDS
+
+for TC in "${SELECTED[@]}"; do
+    if [ -z "${TOOLCHAINS[$TC]+x}" ]; then
+        echo -e "${RED}Unknown toolchain: ${TC}${NC}"
+        echo "Available: ${!TOOLCHAINS[*]}"
+        exit 1
+    fi
+
+    # shellcheck disable=SC2086
+    build_toolchain "$TC" ${TOOLCHAINS[$TC]} || true
+done
+
+TOTAL_ELAPSED=$(( SECONDS - TOTAL_START ))
+
+echo ""
+echo "============================================================"
+echo "Results (${TOTAL_ELAPSED}s total):"
+echo "============================================================"
+for TC in "${PASSED[@]}"; do
+    echo -e "  ${GREEN}PASS${NC}  ${TC}  (${TIMINGS[$TC]}s)"
+done
+for TC in "${FAILED[@]}"; do
+    echo -e "  ${RED}FAIL${NC}  ${TC}  (${TIMINGS[$TC]}s)"
+done
+
+[ ${#FAILED[@]} -eq 0 ]
diff --git a/thirdparty/asio/asio/include/asio/detail/io_uring_service.hpp b/thirdparty/asio/asio/include/asio/detail/io_uring_service.hpp
index 7cc6cc51b..f76ac953a 100644
--- a/thirdparty/asio/asio/include/asio/detail/io_uring_service.hpp
+++ b/thirdparty/asio/asio/include/asio/detail/io_uring_service.hpp
@@ -50,7 +50,7 @@ private:
 public:
   enum op_types { read_op = 0, write_op = 1, except_op = 2, max_ops = 3 };
 
-  class io_object;
+  struct io_object;
 
   // An I/O queue stores operations that must run serially.
   class io_queue : operation
diff --git a/thirdparty/xmake.lua b/thirdparty/xmake.lua
index 59233649a..f06eb6fff 100644
--- a/thirdparty/xmake.lua
+++ b/thirdparty/xmake.lua
@@ -67,7 +67,11 @@ target('cpr')
 target('asio')
     set_kind('headeronly')
     set_group('thirdparty')
-    add_defines("ASIO_STANDLONE", "ASIO_HEADER_ONLY", {public=true})
+    add_defines("ASIO_STANDALONE", "ASIO_HEADER_ONLY", {public=true})
+    if is_plat("linux") and not (get_config("toolchain") == "ue-clang") then
+        add_defines("ASIO_HAS_IO_URING", {public=true})
+        add_packages("liburing", {public=true})
+    end
     add_headerfiles("asio/asio/include/**.hpp")
     add_includedirs("asio/asio/include", {public=true})
 
diff --git a/xmake.lua b/xmake.lua
index 49dd3058f..4110f25e2 100644
--- a/xmake.lua
+++ b/xmake.lua
@@ -202,6 +202,8 @@ if is_os("linux") or is_os("macosx") then
     add_cxxflags("-Wno-unused-value")
     add_cxxflags("-Wno-unused-variable")
     add_cxxflags("-Wno-vla-cxx-extension")
+    -- GCC false positive: constinit static locals used by reference are reported as unused-but-set
+    add_cxxflags("-Wno-unused-but-set-variable", {tools="gcc"})
 end
 
 if get_config("toolchain") == "clang-cl" then