From 3dc5722d5c7673a879f2b4680369d3ac8b6b64b6 Mon Sep 17 00:00:00 2001
From: Tom Stellard <tstellar@redhat.com>
Date: Wed, 4 Aug 2021 14:05:38 -0700
Subject: [PATCH] cmake: Allow shared libraries to customize the soname using
 LLVM_ABI_REVISION

The LLVM_ABI_REVISION variable is intended to be used for release
candidates which introduce an ABI change to a shared library.  This
variable can be specified per library, so there is not one global value
for all of LLVM.

For example, if we LLVM X.0.0-rc2 introduces an ABI change for a library
compared with LLVM X.0.0-rc1, then the LLVM_ABI_REVISION number for
library will be incremented by 1.

In the main branch, LLVM_ABI_REVISION should always be 0, it is only
meant to be used in the release branch.

Differential Revision: https://reviews.llvm.org/D105594
---
 llvm/cmake/modules/AddLLVM.cmake       | 7 +++++--
 llvm/tools/llvm-shlib/CMakeLists.txt   | 9 +++++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 3e009f5061d3..a09405a1be3e 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -586,11 +586,14 @@ function(llvm_add_library name)
     # Set SOVERSION on shared libraries that lack explicit SONAME
     # specifier, on *nix systems that are not Darwin.
     if(UNIX AND NOT APPLE AND NOT ARG_SONAME)
+      if (NOT LLVM_ABI_REVISION)
+        set(LLVM_ABI_REVISION 0)
+      endif()
       set_target_properties(${name}
         PROPERTIES
         # Since 4.0.0, the ABI version is indicated by the major version
-        SOVERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}
-        VERSION ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX})
+	SOVERSION ${LLVM_VERSION_MAJOR}.${LLVM_ABI_REVISION}
+	VERSION ${LLVM_VERSION_MAJOR}.${LLVM_ABI_REVISION})
     endif()
   endif()
 
diff --git a/llvm/tools/llvm-shlib/CMakeLists.txt b/llvm/tools/llvm-shlib/CMakeLists.txt
index 76b9a25cbbcd..b876e7fed6b5 100644
--- a/llvm/tools/llvm-shlib/CMakeLists.txt
+++ b/llvm/tools/llvm-shlib/CMakeLists.txt
@@ -2,6 +2,11 @@
 # library is enabled by setting LLVM_BUILD_LLVM_DYLIB=yes on the CMake
 # commandline. By default the shared library only exports the LLVM C API.
 
+# In the main branch, LLVM_ABI_REVISION should always be 0.  In the release
+# branches, this should be incremented before each release candidate every
+# time the ABI of libLLVM.so changes.
+set(LLVM_ABI_REVISION 0 CACHE STRING "ABI Revision number for SONAMEs (default: 0)")
+
 set(SOURCES
   libllvm.cpp
   )
@@ -67,6 +72,10 @@ if(LLVM_BUILD_LLVM_DYLIB)
     set_property(TARGET LLVM APPEND_STRING PROPERTY
                 LINK_FLAGS
                 " -compatibility_version 1 -current_version ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}")
+  else()
+    set_target_properties(LLVM
+      PROPERTIES
+      SOVERSION ${LLVM_ABI_REVISION})
   endif()
 
   if(TARGET libLLVMExports)
-- 
2.27.0