From c3115285164b7c3762be12c2925d7ec76106e6f6 Mon Sep 17 00:00:00 2001
From: Mehdi Amini <mehdi.amini@apple.com>
Date: Fri, 18 Nov 2016 17:28:10 +0000
Subject: [PATCH] Add link-time detection of LLVM_ABI_BREAKING_CHECKS mismatch

Summary:
LLVM will define a symbol, either EnableABIBreakingChecks or
DisableABIBreakingChecks depending on the configuration setting for
LLVM_ABI_BREAKING_CHECKS.

The llvm-config.h header will add weak references to these symbols in
every clients that includes this header. This should ensure that
a mismatch triggers a link failure (or a load time failure for DSO).

On MSVC, the pragma "detect_mismatch" is used instead.

Reviewers: rnk, jroelofs

Subscribers: llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D26841

llvm-svn: 287352
---
 llvm/include/llvm/Config/llvm-config.h.cmake | 21 +++++++++++++++++++++
 llvm/lib/Support/Error.cpp                   | 16 ++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/llvm/include/llvm/Config/llvm-config.h.cmake b/llvm/include/llvm/Config/llvm-config.h.cmake
index 4121e86..fad1bd1 100644
--- a/llvm/include/llvm/Config/llvm-config.h.cmake
+++ b/llvm/include/llvm/Config/llvm-config.h.cmake
@@ -80,4 +80,25 @@
 /* LLVM version string */
 #define LLVM_VERSION_STRING "${PACKAGE_VERSION}"
 
+// ABI_BREAKING_CHECKS protection: provides link-time failure when clients build
+// mismatch with LLVM
+#if defined(_MSC_VER)
+// Use pragma with MSVC
+#define LLVM_XSTR(s) LLVM_STR(s)
+#define LLVM_STR(s) #s
+#pragma detect_mismatch("LLVM_ENABLE_ABI_BREAKING_CHECKS", LLVM_XSTR(LLVM_ENABLE_ABI_BREAKING_CHECKS))
+#undef LLVM_XSTR
+#undef LLVM_STR
+#elif defined(__cplusplus)
+namespace llvm {
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+extern int EnableABIBreakingChecks;
+__attribute__((weak, visibility ("hidden"))) int *VerifyEnableABIBreakingChecks = &EnableABIBreakingChecks;
+#else
+extern int DisableABIBreakingChecks;
+__attribute__((weak, visibility ("hidden"))) int *VerifyDisableABIBreakingChecks = &DisableABIBreakingChecks;
+#endif
+}
+#endif // _MSC_VER
+
 #endif
diff --git a/llvm/lib/Support/Error.cpp b/llvm/lib/Support/Error.cpp
index 7436a1f..f818868 100644
--- a/llvm/lib/Support/Error.cpp
+++ b/llvm/lib/Support/Error.cpp
@@ -112,3 +112,19 @@ void report_fatal_error(Error Err, bool GenCrashDiag) {
 }
 
 }
+
+
+#ifndef _MSC_VER
+namespace llvm {
+
+// One of these two variables will be referenced by a symbol defined in
+// llvm-config.h. We provide a link-time (or load time for DSO) failure when
+// there is a mismatch in the build configuration of the API client and LLVM.
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+int EnableABIBreakingChecks;
+#else
+int DisableABIBreakingChecks;
+#endif
+
+} // end namespace llvm
+#endif
\ No newline at end of file
-- 
2.7.4