[Lldb-commits] [lldb] ff67b68 - [lldb] On POSIX, check for duplicate interpreter modules without loading them (#69932)

[via lldb-commits]

Author: David Spickett
Date: 2023-10-25T10:12:45+01:00
New Revision: ff67b68e43db5b4feb46670445561fab976fb0ef

URL: https://github.com/llvm/llvm-project/commit/ff67b68e43db5b4feb46670445561fab976fb0ef
DIFF: https://github.com/llvm/llvm-project/commit/ff67b68e43db5b4feb46670445561fab976fb0ef.diff

LOG: [lldb] On POSIX, check for duplicate interpreter modules without loading them (#69932)

Fixes #68987

Early on we load the interpreter (most commonly ld-linux) in
LoadInterpreterModule. Then later when we get the first DYLD rendezvous
we get a list of libraries that commonly includes ld-linux again.

Previously we would load this duplicate, see that it was a duplicate,
and unload it.

Problem was that this unloaded the section information of the first copy
of ld-linux. On platforms where you can place a breakpoint using only an
address, this wasn't an issue.

On ARM you have ARM and Thumb modes. We must know which one the section
we're breaking in is, otherwise we'll go there in the wrong mode and
SIGILL. This happened on ARM when lldb tried to call mmap during
expression evaluation.

To fix this, I am making the assumption that the base address we see in
the module prior to loading can be compared with what we know the
interpreter base address is. Then we don't have to load the module to
know we can ignore it.

This fixes the lldb test suite on Ubuntu versions where
https://bugs.launchpad.net/ubuntu/+source/gdb/+bug/1927192 has been
fixed. Which was recently done on Jammy.

Added: 
    

Modified: 
    lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp b/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
index c427b476089e458..3d65f496742099d 100644
--- a/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
+++ b/lldb/source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp
@@ -437,6 +437,14 @@ void DynamicLoaderPOSIXDYLD::RefreshModules() {
       m_initial_modules_added = true;
     }
     for (; I != E; ++I) {
+      // Don't load a duplicate copy of ld.so if we have already loaded it
+      // earlier in LoadInterpreterModule. If we instead loaded then unloaded it
+      // later, the section information for ld.so would be removed. That
+      // information is required for placing breakpoints on Arm/Thumb systems.
+      if ((m_interpreter_module.lock() != nullptr) &&
+          (I->base_addr == m_interpreter_base))
+        continue;
+
       ModuleSP module_sp =
           LoadModuleAtAddress(I->file_spec, I->link_addr, I->base_addr, true);
       if (!module_sp.get())
@@ -450,15 +458,6 @@ void DynamicLoaderPOSIXDYLD::RefreshModules() {
         } else if (module_sp == interpreter_sp) {
           // Module already loaded.
           continue;
-        } else {
-          // If this is a duplicate instance of ld.so, unload it.  We may end
-          // up with it if we load it via a 
diff erent path than before
-          // (symlink vs real path).
-          // TODO: remove this once we either fix library matching or avoid
-          // loading the interpreter when setting the rendezvous breakpoint.
-          UnloadSections(module_sp);
-          loaded_modules.Remove(module_sp);
-          continue;
         }
       }