Fix a segfault when _dyld_shared_cache_contains_path is not available

The _dyld_shared_cache_contains_path is only available in macOS 11.0 or later. As we are compiling in a new system that's newer than 11.0 but setting the deployment target to an older version, it's possible that the _dyld_shared_cache_contains_path is not available in the target platform and in that case we will segfault when calling it. It's also possible that when compiling memray in an old system _dyld_shared_cache_contains_path is not even prototyped in the headers. To handle this, we change to fetch the function via a dlopen/dlsym approach that will be generic in all macOS versions at the cost of an extra call to dlopen the first time we interpose symbols. Signed-off-by: Pablo Galindo <[email protected]>
bloomberg · May 30, 2024 · 7337dae · 7337dae
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diff --git a/news/615.bugfix.rst b/news/615.bugfix.rst
@@ -0,0 +1 @@
+Fix a crash in old macOS versions (<11.0) due to the inavailability of some linker cache APIs.
diff --git a/src/memray/_memray/macho_shenanigans.cpp b/src/memray/_memray/macho_shenanigans.cpp
@@ -296,7 +296,23 @@ patch_symbols_in_shared_object(
             unsigned int section_type = section->flags & SECTION_TYPE;
             LOG(DEBUG) << "Considering section " << i << " (" << section->segname << ":"
                        << section->sectname << ")";
-            if (_dyld_shared_cache_contains_path(image_name) && strcmp(section->segname, SEG_TEXT) == 0)
+
+            // dlopen with null and check for _dyld_shared_cache_contains_path but do it only
+            // once with std::once_flag
+            static std::function<bool(const char*)> dyld_shared_cache_contains_path;
+            static std::once_flag _dyld_shared_cache_check_flag;
+            std::call_once(_dyld_shared_cache_check_flag, [&]() {
+                void* handle = dlopen(nullptr, RTLD_LAZY);
+                dyld_shared_cache_contains_path = (bool(*)(const char *))(
+                        dlsym(handle, "_dyld_shared_cache_contains_path")
+                );
+                dlclose(handle);
+            });
+
+
+            if (dyld_shared_cache_contains_path && 
+                _dyld_shared_cache_contains_path(image_name) &&
+                strcmp(section->segname, SEG_TEXT) == 0)
             {
                 // Shared libraries that are part of the shared cache will have the symbols we are
                 // looking for in the __stubs/__auth_stubs PLT section pointing to a GOT that we cannot