https://llvm.org/bugs/show_bug.cgi?id=28831
Bug ID: 28831
Summary: Bad logic around CMAKE_OSX_SYSROOT and
CMAKE_OSX_ARCHITECTURES
Product: libc++
Version: 3.9
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: da...@bamsoftware.com
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
Classification: Unclassified
Created attachment 16870
--> https://llvm.org/bugs/attachment.cgi?id=16870&action=edit
Fixes CMake logic around some Mac variables.
I'm using CMake v2.8.12.2 and building libcxx like this:
cd libcxx
mkdir build
cd build
cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE:STRING=Release
-DCMAKE_C_FLAGS="-target x86_64-apple-darwin10" -DCMAKE_CXX_FLAGS="-target
x86_64-apple-darwin10" -DCMAKE_SYSTEM_NAME=Darwin
-DCMAKE_OSX_SYSROOT=/home/build/MacOSX10.7.sdk -DLLVM_PATH=$HOME/llvm ..
I'm cross compiling from GNU/Linux (Debian) to x86_64-apple-darwin10.
There is a bug in lib/CMakeLists.txt's handling of CMAKE_OSX_SYSROOT.
lib/CMakeLists.txt has this code that doesn't do what it is apparently
trying to do (I added comments for branch labels):
if ( ${CMAKE_OSX_SYSROOT} )
# Branch A
list(FIND ${CMAKE_OSX_ARCHITECTURES} "armv7" OSX_HAS_ARMV7)
if (OSX_HAS_ARMV7)
# Branch C
set(OSX_RE_EXPORT_LINE
"${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib"
"-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++sjlj-abi.exp")
else()
# Branch D
set(OSX_RE_EXPORT_LINE
"-Wl,-reexport_library,${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib")
endif()
else()
# Branch B
set(OSX_RE_EXPORT_LINE "/usr/lib/libc++abi.dylib
-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
endif()
By setting CMAKE_OSX_SYSROOT and leaving CMAKE_OSX_ARCHITECTURES blank,
I expected Branch D to be run. Instead, Branch B is always run.
The first bug is in the syntax of the toplevel "if", which causes it to
be false even if CMAKE_OSX_SYSROOT is defined. According to the CMake
documentation,
https://cmake.org/cmake/help/v3.3/command/if.html#command:if
"The if command was written very early in CMake’s history,
predating the ${} variable evaluation syntax, and for
convenience evaluates variables named by its arguments as shown
in the above signatures. Note that normal variable evaluation
with ${} applies before the if command even receives the
arguments."
The way the condition is written is causing CMAKE_OSX_SYSROOT to be
dereferenced twice instead of once. It should instead be:
if ( CMAKE_OSX_SYSROOT )
or perhaps better:
if ( DEFINED CMAKE_OSX_SYSROOT )
After the "if", there is another bug. This code appears to be checking
for "armv7" in CMAKE_OSX_ARCHITECTURES:
list(FIND ${CMAKE_OSX_ARCHITECTURES} "armv7" OSX_HAS_ARMV7)
if (OSX_HAS_ARMV7)
The code treats OSX_HAS_ARMV7 as if it were a boolean, but according to
the documentation, it is an index where -1 means not found:
https://cmake.org/cmake/help/v3.3/command/list.html#command:list
"FIND will return the index of the element specified in the list
or -1 if it wasn’t found."
-1 is treated as a true value, so the condition is true except when
"armv7" is the zeroth element of CMAKE_OSX_ARCHITECTURES. According to
http://www.vtk.org/Wiki/CMake/Examples#Check_if_a_list_contains_a_value,
the way to check for list membership is:
list(FIND "${CMAKE_OSX_ARCHITECTURES}" "armv7" OSX_HAS_ARMV7)
if (NOT OSX_HAS_ARMV7 EQUAL -1)
I don't know much about CMake, but the attached patch was sufficient to
get Branch D to execute for me and get the SDK path into
OSX_RE_EXPORT_LINE.
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