[llvm] [LTO] Fix a use-after-free in legacy LTO C APIs (PR #107896)

[Steven Wu via llvm-commits]

https://github.com/cachemeifyoucan created https://github.com/llvm/llvm-project/pull/107896

Fix a bug that `lto_runtime_lib_symbols_list` is returning the address
of a local variable that will be freed when getting out of scope. This
is a regression from #98512 that rewrites the runtime libcall function
lists into a SmallVector.

rdar://135559037


>From be7a8bf322407fd7a2a7b51b172cafdf53f91105 Mon Sep 17 00:00:00 2001
From: Steven Wu <stevenwu at apple.com>
Date: Mon, 9 Sep 2024 11:21:24 -0700
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.5
---
 llvm/tools/lto/lto.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/tools/lto/lto.cpp b/llvm/tools/lto/lto.cpp
index d68cff839604f6..c8fbbd1e0b24b7 100644
--- a/llvm/tools/lto/lto.cpp
+++ b/llvm/tools/lto/lto.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm-c/lto.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/CodeGen/CommandFlags.h"
@@ -88,6 +89,8 @@ struct LTOToolDiagnosticHandler : public DiagnosticHandler {
   }
 };
 
+static SmallVector<const char *> RuntimeLibcallSymbols;
+
 // Initialize the configured targets if they have not been initialized.
 static void lto_initialize() {
   if (!initialized) {
@@ -108,6 +111,7 @@ static void lto_initialize() {
     LTOContext = &Context;
     LTOContext->setDiagnosticHandler(
         std::make_unique<LTOToolDiagnosticHandler>(), true);
+    RuntimeLibcallSymbols = lto::LTO::getRuntimeLibcallSymbols(Triple());
     initialized = true;
   }
 }
@@ -691,7 +695,6 @@ extern const char *lto_input_get_dependent_library(lto_input_t input,
 }
 
 extern const char *const *lto_runtime_lib_symbols_list(size_t *size) {
-  auto symbols = lto::LTO::getRuntimeLibcallSymbols(Triple());
-  *size = symbols.size();
-  return symbols.data();
+  *size = RuntimeLibcallSymbols.size();
+  return RuntimeLibcallSymbols.data();
 }