[XRay] [compiler-rt] [DSO] start deciding which symbols to hide/export

[pelikan]

Summary

Since a running application will only have one set of XRay handlers, its
C++ function pointers all trampolines go to need to be explicitly put to
.dynsym for the runtime dynamic loader to find them. In contrast, local
symbols like the instrumentation map demarcation points, trampolines and
DSOContext must *not* be visible outside whatever we're linking, because
the world is full of broken software (libtool) instructing the toolchain
to apply broad policies on all symbols (-z defs, --export-dynamic) which
might confuse the loader into treating one DSO's instrumentation map for
other one's, for example, because the wrong visibilities have been set.

Therefore we'll maintain an explicit list of interfaces we want to share
and later (when this won't break any tests and I verify the install rule
does what I want in Gentoo's llvm-9999.ebuild) we'll instruct the driver
in Clang to pass these files as --dynamic-list and --version-script into
the final linker invocation. It will use the same /usr/lib/clang/7.0.0/
path as the XRay .a (+all sanitizers with their own .syms) currently do.

Obviously, this list will probably be altered later, as we progress.

[pelikan]

rebase + try to use this diff from a different machine

[pelikan]

sync & add a failing test

[pelikan]

more tidbits and context

lib/xray/CMakeLists.txt

foreach(arch ${XRAY_SUPPORTED_ARCH})
     # Common XRay archive for instrumented binaries.
     add_compiler_rt_runtime(clang_rt.xray
      STATIC
      ARCHS ${arch}
      CFLAGS ${XRAY_CFLAGS}
      DEFS ${XRAY_COMMON_DEFINITIONS}
      OBJECT_LIBS ${XRAY_COMMON_RUNTIME_OBJECT_LIBS} RTXray
      PARENT_TARGET xray)
+    set(syms ${COMPILER_RT_LIBRARY_OUTPUT_DIR}/libclang_rt.xray-${arch}.a.syms)
+    set(vers ${COMPILER_RT_LIBRARY_OUTPUT_DIR}/libclang_rt.xray-${arch}.a.vers)
+    add_custom_command(TARGET xray
+      COMMAND /bin/cp xray.syms ${syms}
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+      VERBATIM)
+    add_custom_command(TARGET xray
+      COMMAND /bin/cp xray.vers ${vers}
+      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+      VERBATIM)
+    install(FILES ${syms} ${vers}
+      DESTINATION ${COMPILER_RT_LIBRARY_INSTALL_DIR})
     # FDR mode runtime archive (addon for clang_rt.xray)
     add_compiler_rt_runtime(clang_rt.xray-fdr
       STATIC
       ARCHS ${arch}
       CFLAGS ${XRAY_CFLAGS}
       DEFS ${XRAY_COMMON_DEFINITIONS}
       OBJECT_LIBS RTXrayFDR
       PARENT_TARGET xray)

lib/xray/xray.syms

+{
+  extern "C++" {
+    __xray::XRayPatchedCustomEvent;
+    __xray::XRayPatchedFunction;
+    __xray::XRayArgLogger;
+  };
+  XRayInitialized;
+};

lib/xray/xray.vers

+{
+global:
+  extern "C++" {
+    __xray::XRayPatchedCustomEvent;
+    __xray::XRayPatchedFunction;
+    __xray::XRayArgLogger;
+  };
+  XRayInitialized;
+local:
+  extern "C++" {
+    __xray::DSOContext;
+  };
+  __start_xray_instr_map;
+  __start_xray_fn_idx;
+  __stop_xray_instr_map;
+  __stop_xray_fn_idx;
+  __xray_ArgLoggerEntry;
+  __xray_FunctionEntry;
+  __xray_FunctionExit;
+  __xray_FunctionTailExit;
+  __xray_CustomEvent;
+  __xray_patch;
+};

test/xray/TestCases/Posix/symbol-visibility.cc

+// Test to check if XRay runtime symbols have the expected visibility.
+//
+// RUN: %clangxx_xray -fuse-ld=gold -fxray-instrument %s -Wl,-verbose -v -o %t
+// RUN: %llvm_objdump -t %t | FileCheck %s
+//
+// XXX STILL WORK IN PROGRESS!
+// XXX needs https://bugs.llvm.org/show_bug.cgi?id=35838 to be fixed, at least
+//
+// REQUIRES: linux && fixing-lld
+// XFAIL: x86_64
+// (xfail until the corresponding clang change in D45570 is committed)
+
+[[clang::xray_always_instrument]] int main() { return 0; }
+
+// CHECK: SYMBOL TABLE:
+// CHECK: _ZN6__xray13XRayArgLoggerE
+// CHECK: _ZN6__xray22XRayPatchedCustomEventE
+// CHECK: _ZN6__xray19XRayPatchedFunctionE
+// CHECK-NOT: __xray_FunctionEntry
+// CHECK-NOT: __xray_FunctionExit
+// CHECK-NOT: __xray_FunctionTailExit
+// CHECK-NOT: __xray_ArgLoggerEntry
+// CHECK-NOT: __xray_CustomEvent
+// CHECK-NOT: __start_xray_instr_map
+// CHECK-NOT: __stop_xray_instr_map
+// CHECK-NOT: __start_xray_fn_index
+// CHECK-NOT: __stop_xray_fn_index

test/xray/lit.cfg

config.substitutions.append(
      build_invocation(config.cxx_mode_flags + [config.target_cflags])))
 config.substitutions.append(
     ('%clang_xray ', build_invocation(clang_xray_cflags)))
 config.substitutions.append(
     ('%clangxx_xray', build_invocation(clang_xray_cxxflags)))
 config.substitutions.append(
     ('%llvm_xray', llvm_xray))
 config.substitutions.append(
+    ('%llvm_objdump ', os.path.join(config.llvm_tools_dir, 'llvm-objdump ')))
+config.substitutions.append(
     ('%xraylib',
         ('-lm -lpthread %s -lrt -L%s '
          '-Wl,-whole-archive -lclang_rt.xray-%s -Wl,-no-whole-archive')
         % (libdl_flag, config.compiler_rt_libdir, host_arch)))
 
 # Default test suffixes.
 config.suffixes = ['.c', '.cc', '.cpp']
 
 if config.host_os not in ['FreeBSD', 'Linux', 'NetBSD']:
   config.unsupported = True
 elif '64' not in config.host_arch:
   if 'arm' in config.host_arch:
     if '-mthumb' in config.target_cflags:
       config.unsupported = True
   else:
     config.unsupported = True