Simplify library usage as submodule in other projects

CMakeLists.txt

@@ -85,13 +85,17 @@ endif()
 
 add_subdirectory(contrib/liburing-cmake)
 add_subdirectory(contrib/librseq-cmake)
-add_subdirectory(contrib/libbacktrace-cmake)
 add_subdirectory(contrib/googletest-cmake)
 add_subdirectory(contrib/benchmark-cmake)
 add_subdirectory(contrib/systemtap-sdt)
 add_subdirectory(contrib/libbpf-cmake)
 add_subdirectory(contrib/bpftool-cmake)
 
+option(BUILD_LIBBACKTRACE "Build libbacktrace (used to symbolize stack traces on SILK_ASSERT failure and by the profiler)" ON)
+if(BUILD_LIBBACKTRACE)
+    add_subdirectory(contrib/libbacktrace-cmake)
+endif()
+
 option(BUILD_POCO "Build Poco library (required by http-perf)" OFF)
 if(BUILD_POCO)
     add_subdirectory(contrib/poco-cmake)
@@ -135,5 +139,8 @@ if(NOT SANITIZER STREQUAL "memory")
     # Boost::context (used by silk) is assembly-level and has no std::string
     # in its ABI, so it works with libc++ despite being a system library.
     add_subdirectory(src/perf)
-    add_subdirectory(src/profiler)
+    if(BUILD_LIBBACKTRACE)
+        # symbolizer.cpp depends directly on <backtrace.h>.
+        add_subdirectory(src/profiler)
+    endif()
 endif()

include/silk/util/platform.h

@@ -10,7 +10,23 @@
 #include <time.h>
 #include <unistd.h>
 
-#include <sys/rseq.h>
+/**
+ * On older sysroots we fall back to a minimal in-tree `struct rseq` matching
+ * the kernel UAPI layout (cpu_id_start at offset 0, cpu_id at offset 4) and
+ * alias `__rseq_offset` to librseq's `rseq_offset`, which librseq populates.
+ */
+#if __has_include(<sys/rseq.h>)
+#    include <sys/rseq.h>
+#else
+#    include <stddef.h>
+struct rseq
+{
+    uint32_t cpu_id_start;
+    uint32_t cpu_id;
+};
+extern "C" ptrdiff_t rseq_offset;
+#    define __rseq_offset rseq_offset
+#endif
 
 /** Suppress unused-variable warnings. */
 #define SILK_UNUSED(x) (void)(x)

src/util/CMakeLists.txt

@@ -1,7 +1,15 @@
 file(GLOB UTIL_SOURCES CONFIGURE_DEPENDS *.cpp)
 
 add_library(silk-util ${UTIL_SOURCES})
-target_link_libraries(silk-util PRIVATE Libbacktrace::Libbacktrace Librseq::Librseq)
+target_link_libraries(silk-util
+    PUBLIC  Boost::headers
+    PRIVATE Librseq::Librseq
+)
+
+if(BUILD_LIBBACKTRACE)
+    target_compile_definitions(silk-util PRIVATE SILK_USE_LIBBACKTRACE)
+    target_link_libraries(silk-util PRIVATE Libbacktrace::Libbacktrace)
+endif()
 
 add_subdirectory(tests)
 add_subdirectory(benchmarks)

src/util/assert.cpp

@@ -2,14 +2,18 @@
 
 #include <silk/util/platform.h>
 
+#include <cstdio>
 #include <cstdlib>
-#include <cstring>
-#include <format>
 #include <sstream>
-#include <string_view>
 
-#include <backtrace.h>
-#include <cxxabi.h>
+#if defined(SILK_USE_LIBBACKTRACE)
+#    include <cstring>
+#    include <format>
+#    include <string_view>
+
+#    include <backtrace.h>
+#    include <cxxabi.h>
+#endif // SILK_USE_LIBBACKTRACE
 
 namespace silk
 {
@@ -19,6 +23,8 @@ static constexpr const char * COLOR_RED = "\033[1;31m";
 static constexpr const char * COLOR_YELLOW = "\033[0;33m";
 static constexpr const char * COLOR_GREEN = "\033[0;32m";
 
+#if defined(SILK_USE_LIBBACKTRACE)
+
 static void btCreateErrorCallback(void * data, const char * msg, int err) noexcept
 {
     SILK_UNUSED(data);
@@ -74,6 +80,8 @@ static void btErrorCallback(void * data, const char * msg, int err) noexcept
     (*ctx->out) << "  backtrace error " << err << ": " << msg << "\n";
 }
 
+#endif // SILK_USE_LIBBACKTRACE
+
 void assertFail(const char * message, const char * file, int line, const char * details) noexcept
 {
     std::ostringstream out;
@@ -84,8 +92,10 @@ void assertFail(const char * message, const char * file, int line, const char *
     }
     out << COLOR_RESET << "\n";
 
+#if defined(SILK_USE_LIBBACKTRACE)
     Context ctx{&out, 0};
     backtrace_full(btState, 0, btCallback, btErrorCallback, &ctx);
+#endif
 
     std::fputs(out.str().c_str(), stderr);
     std::fflush(stderr);