Avoid patching symbols in the extension module

The fact that patching ourselves had not raised problems so far its really an outstanding fact in this universe. Unfortunately seems that with the latest toolchain + GCC there is something that causes memray to point the d_original entry of the hooks pointing to itself, which should never happen. To fix this resiliently, avoid patching ourselves by getting our own name in the extension module and then avoiding that shared object. Signed-off-by: Pablo Galindo <pablogsal@gmail.com>
bloomberg · Sep 19, 2024 · 1983853 · 1983853
1 parent 8635569
commit 1983853
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Showing 3 changed files with 20 additions and 5 deletions.
diff --git a/news/685.bugfix.rst b/news/685.bugfix.rst
@@ -0,0 +1 @@
+Fix some crashes caused by interposing symbols in memray itself
diff --git a/src/memray/_memray/elf_shenanigans.cpp b/src/memray/_memray/elf_shenanigans.cpp
@@ -17,7 +17,8 @@ namespace {
 struct elf_patcher_context_t
 {
     bool restore_original;
-    std::set<std::string> patched;
+    std::set<std::string>& patched;
+    const std::string& self_so_name;
 };
 
 }  // namespace
@@ -172,10 +173,10 @@ phdrs_callback(dl_phdr_info* info, [[maybe_unused]] size_t size, void* data) noe
     }
 
     if (strstr(info->dlpi_name, "/ld-linux") || strstr(info->dlpi_name, "/ld-musl")
-        || strstr(info->dlpi_name, "linux-vdso.so.1"))
+        || strstr(info->dlpi_name, "linux-vdso.so.1")
+        || strstr(info->dlpi_name, context.self_so_name.c_str()))
     {
         // Avoid chaos by not overwriting the symbols in the linker.
-        // TODO: Don't override the symbols in our shared library!
         return 0;
     }
 
@@ -198,14 +199,14 @@ phdrs_callback(dl_phdr_info* info, [[maybe_unused]] size_t size, void* data) noe
 void
 SymbolPatcher::overwrite_symbols() noexcept
 {
-    elf_patcher_context_t context{false, symbols};
+    elf_patcher_context_t context{false, symbols, self_so_name};
     dl_iterate_phdr(&phdrs_callback, (void*)&context);
 }
 
 void
 SymbolPatcher::restore_symbols() noexcept
 {
-    elf_patcher_context_t context{true, symbols};
+    elf_patcher_context_t context{true, symbols, self_so_name};
     dl_iterate_phdr(&phdrs_callback, (void*)&context);
 }
 

diff --git a/src/memray/_memray/linker_shenanigans.h b/src/memray/_memray/linker_shenanigans.h
@@ -3,14 +3,27 @@
 #include <set>
 #include <string>
 
+#include <dlfcn.h>
+
 namespace memray::linker {
 
+static void
+_dummy(void){};
+
 class SymbolPatcher
 {
   private:
     std::set<std::string> symbols;
+    std::string self_so_name = "_memray.cpython-";
 
   public:
+    SymbolPatcher()
+    {
+        Dl_info info;
+        if (dladdr((void*)&_dummy, &info)) {
+            self_so_name = info.dli_fname;
+        }
+    }
     void overwrite_symbols() noexcept;
     void restore_symbols() noexcept;
 };