Add link-time detection of LLVM_ABI_BREAKING_CHECKS mismatch

[mehdi_amini]

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.

[mehdi_amini]

Note: I haven't tested the MSVC pragma path, this is just based on the doc.

[mehdi_amini]

Mark the uses of the symbols with hidden visibility

[jroelofs]

llvm/include/llvm/Config/llvm-config.h.cmake

99

My notes had a typo: s/VDisable/Disable/

[jroelofs]

The non-msvc side of this otherwise LGTM, btw.

[mehdi_amini]

Fix typo

[mehdi_amini]

Thanks!
I'll wait for @rnk for the Windows side.

llvm/include/llvm/Config/llvm-config.h.cmake

99

Yeah I noticed when testing, but apparently I git stash and failed to amend the commit before running arc diff

[rnk]

lgtm

llvm/include/llvm/Config/llvm-config.h.cmake

 #define LLVM_VERSION_MINOR ${LLVM_VERSION_MINOR}
 
 /* Patch version of the LLVM API */
 #define LLVM_VERSION_PATCH ${LLVM_VERSION_PATCH}
 
 /* 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)) int *VerifyEnableABIBreakingChecks = &EnableABIBreakingChecks;
+#else
+extern int DisableABIBreakingChecks;
+__attribute__((weak)) int *VerifyDisableABIBreakingChecks = &VDisableABIBreakingChecks;
+#endif
+}
+#endif // _MSC_VER
+
 #endif

llvm/lib/Support/Error.cpp

void report_fatal_error(Error Err, bool GenCrashDiag) {
   {
     raw_string_ostream ErrStream(ErrMsg);
     logAllUnhandledErrors(std::move(Err), ErrStream, "");
   }
   report_fatal_error(ErrMsg);
 }
 
 }
+
+
+#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