[llvm] dc67340 - [CMake] Remove -Wl, -allow-shlib-undefined which was added in rL221530

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-09-01T21:13:45-07:00
New Revision: dc6734020844e92feef0ab3e3714f01d2bb98ea4

URL: https://github.com/llvm/llvm-project/commit/dc6734020844e92feef0ab3e3714f01d2bb98ea4
DIFF: https://github.com/llvm/llvm-project/commit/dc6734020844e92feef0ab3e3714f01d2bb98ea4.diff

LOG: [CMake] Remove -Wl,-allow-shlib-undefined which was added in rL221530

In GNU ld, gold and LLD, --no-allow-shlib-undefined is the default when
linking an executable. The option disallows unresolved symbols in shared objects.
(gold and LLD catch fewer cases than GNU ld. See D57385 for details)
See D57569 why it is bad idea to use --allow-shlib-undefined for executables [a].

GNU ld traditionally copied DT_NEEDED entries transitively. This was
deemed not good, so GNU ld 2.22 defaulted to --no-copy-dt-needed-entries.
gold and LLD always behave like --no-copy-dt-needed-entries.
rL221530 added -Wl,-allow-shlib-undefined to make some old releases of GNU ld's
--no-copy-dt-needed-entries to actually work.

Due to [a] and [b], this patch drops -Wl,-allow-shlib-undefined.

[b]: In a -DBUILD_SHARED_LIBS=on build, `--as-needed --allow-shlib-undefined`
can unexpectedly suppress some .dynsym entries.  The issue can cause
mlir-cpu-runner to fail at runtime. Note, on Debian, gcc newer than (gcc-9-20190125-2) enable
--as-needed by default.
See https://sourceware.org/bugzilla/show_bug.cgi?id=26551 for a reduced example.

Reviewed By: mehdi_amini, echristo

Differential Revision: https://reviews.llvm.org/D86839

Added: 
    

Modified: 
    llvm/CMakeLists.txt

Removed: 
    


################################################################################
diff  --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 10fc8499a92e..4a7639c51121 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -969,16 +969,6 @@ if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
           add_definitions("-D_FILE_OFFSET_BITS=64")
 endif()
 
-# Work around a broken bfd ld behavior. When linking a binary with a
-# foo.so library, it will try to find any library that foo.so uses and
-# check its symbols. This is wasteful (the check was done when foo.so
-# was created) and can fail since it is not the dynamic linker and
-# doesn't know how to handle search paths correctly.
-if (UNIX AND NOT APPLE AND NOT CMAKE_SYSTEM_NAME MATCHES "SunOS|AIX|OS390")
-  set(CMAKE_EXE_LINKER_FLAGS
-      "${CMAKE_EXE_LINKER_FLAGS} -Wl,-allow-shlib-undefined")
-endif()
-
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
 include_directories( ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR})