[compiler-rt] [compiler-rt] Don't rely on automatic codesigning with Apple's linker (PR #91681)

[Julian Lettner via llvm-commits]

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@@ -387,35 +387,35 @@ function(add_compiler_rt_runtime name type)
         set_target_properties(${libname} PROPERTIES IMPORT_SUFFIX ".lib")
       endif()
       if (APPLE AND NOT CMAKE_LINKER MATCHES ".*lld.*")
-        # Ad-hoc sign the dylibs when using Xcode versions older than 12.
-        # Xcode 12 shipped with ld64-609.
-        # FIXME: Remove whole conditional block once everything uses Xcode 12+.
-        set(LD_V_OUTPUT)
+        # Apple's linker signs the resulting dylib with an ad-hoc code signature in
+        # most situations, except:
+        # 1. Versions of ld64 prior to ld64-609 in Xcode 12 predate this behavior.
+        # 2. Apple's new linker does not when building with `-darwin-target-variant`
+        #    to support macOS Catalyst.
+        #
+        # Explicitly re-signing the dylib works around both of these issues. The
+        # signature is marked as `linker-signed` when that is supported so that it
+        # behaves as expected when processed by subsequent tooling.
+        #
+        # Detect whether `codesign` supports `-o linker-signed` by passing it as an
+        # argument and looking for `invalid argument "linker-signed"` in its output.
+        # FIXME: Remove this once all supported toolchains support `-o linker-signed`.
         execute_process(
-          COMMAND sh -c "${CMAKE_LINKER} -v 2>&1 | head -1"
-          RESULT_VARIABLE HAD_ERROR
-          OUTPUT_VARIABLE LD_V_OUTPUT
+          COMMAND sh -c "codesign -f -s - -o linker-signed this-does-not-exist 2>&1 | grep -q linker-signed"
----------------
yln wrote:

This is clever!  Hopefully not too brittle?  Only other thing I can think of is `man codesign | grep linker-signed`, but I like that less because it uses a completely other command (`man`).



https://github.com/llvm/llvm-project/pull/91681