[Lldb-commits] [lldb] [IRInterpreter] Return zero address for missing weak function (PR #93548)

[Nikita Popov via lldb-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/93548

If a weak function is missing, still return it's address (zero) rather than failing interpretation. Otherwise we have a mismatch between Interpret() and CanInterpret() resulting in failures that would not occur with JIT execution.

Alternatively, we could try to look for weak symbols in CanInterpret() and generally reject them there.

This is the root cause for the issue exposed by
https://github.com/llvm/llvm-project/pull/92885. Previously, the case affected by that always fell back to JIT because an icmp constant expression was used, which is not supported by the interpreter. Now a normal icmp instruction is used, which is supported. However, we fail to interpret due to incorrect handling of weak function addresses.

>From 0e74f5e94e99c97a8948a521b270f2e1413cc53b Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Tue, 28 May 2024 15:34:55 +0200
Subject: [PATCH] [IRInterpreter] Return zero address for missing weak function

If a weak function is missing, still return it's address (zero)
rather than failing interpretation. Otherwise we have a mismatch
between Interpret() and CanInterpret() resulting in failures that
would not occur with JIT execution.

Alternatively, we could try to look for weak symbols in
CanInterpret() and generally reject them there.

This is the root cause for the issue exposed by
https://github.com/llvm/llvm-project/pull/92885. Previously,
the case affected by that always fell back to JIT because an
icmp constant expression was used, which is not supported by the
interpreter. Now a normal icmp instruction is used, which is
supported. However, we fail to interpret due to incorrect
handling of weak function addresses.
---
 lldb/source/Expression/IRInterpreter.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lldb/source/Expression/IRInterpreter.cpp b/lldb/source/Expression/IRInterpreter.cpp
index df02922708663..5b670067b5c43 100644
--- a/lldb/source/Expression/IRInterpreter.cpp
+++ b/lldb/source/Expression/IRInterpreter.cpp
@@ -264,7 +264,7 @@ class InterpreterStackFrame {
         lldb_private::ConstString name(constant_func->getName());
         bool missing_weak = false;
         lldb::addr_t addr = m_execution_unit.FindSymbol(name, missing_weak);
-        if (addr == LLDB_INVALID_ADDRESS || missing_weak)
+        if (addr == LLDB_INVALID_ADDRESS)
           return false;
         value = APInt(m_target_data.getPointerSizeInBits(), addr);
         return true;