[Lldb-commits] [PATCH] D98879: [lldb/PlatformPOSIX] Change LoadImage default to RTLD_LAZY

[Vedant Kumar via Phabricator via lldb-commits]

vsk created this revision.
vsk added a reviewer: jingham.
Herald added a subscriber: emaste.
vsk requested review of this revision.
Herald added a project: LLDB.

In general, it seems like the debugger should allow programs to load & run with
libraries as far as possible, instead of defaulting to being super-picky about
unavailable symbols.

This is critical on macOS/Darwin, as libswiftCore.dylib may 1) export a version
symbol using @available markup and then 2) expect that other exported APIs are
only dynamically used once the version symbol is checked. We can't open a
version of the library built with a bleeding-edge SDK on an older OS without
RTLD_LAXY (or pervasive/expensive @available markup added to dyld APIs).

See: https://lists.llvm.org/pipermail/lldb-dev/2021-March/016796.html


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98879

Files:
  lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp


Index: lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
===================================================================
--- lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
+++ lldb/source/Plugins/Platform/POSIX/PlatformPOSIX.cpp
@@ -573,6 +573,21 @@
 std::unique_ptr<UtilityFunction>
 PlatformPOSIX::MakeLoadImageUtilityFunction(ExecutionContext &exe_ctx,
                                             Status &error) {
+  // Use lazy binding so as to not make dlopen()'s success conditional on
+  // forcing every symbol in the library. This is critical on macOS/Darwin, as
+  // a library may 1) export a version symbol using @available markup and then
+  // 2) expect that other exported APIs are only dynamically used once the
+  // version symbol is checked. (Previously, LLDB used RTLD_NOW=2, which made
+  // it impossible to load such libraries (e.g. libswiftCore.dylib)).
+  //
+  // In general, the debugger should allow programs to load & run with
+  // libraries as far as they can, instead of defaulting to being super-picky
+  // about unavailable symbols.
+  //
+  // The value "1" appears to imply lazy binding (RTLD_LAZY) on both Darwin
+  // and other POSIX OSes.
+#define DLOPEN_OPTIONS "1"
+
   // Remember to prepend this with the prefix from
   // GetLibdlFunctionDeclarations. The returned values are all in
   // __lldb_dlopen_result for consistency. The wrapper returns a void * but
@@ -595,7 +610,7 @@
   {
     // This is the case where the name is the full path:
     if (!path_strings) {
-      result_ptr->image_ptr = dlopen(name, 2);
+      result_ptr->image_ptr = dlopen(name, )" DLOPEN_OPTIONS R"();
       if (result_ptr->image_ptr)
         result_ptr->error_str = nullptr;
       return nullptr;
@@ -609,7 +624,7 @@
       buffer[path_len] = '/';
       char *target_ptr = buffer+path_len+1; 
       memcpy((void *) target_ptr, (void *) name, name_len + 1);
-      result_ptr->image_ptr = dlopen(buffer, 2);
+      result_ptr->image_ptr = dlopen(buffer, )" DLOPEN_OPTIONS R"();
       if (result_ptr->image_ptr) {
         result_ptr->error_str = nullptr;
         break;
@@ -620,6 +635,7 @@
     return nullptr;
   }
   )";
+#undef DLOPEN_OPTIONS
 
   static const char *dlopen_wrapper_name = "__lldb_dlopen_wrapper";
   Process *process = exe_ctx.GetProcessSP().get();


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