Why adding the linker flag `-save-temps` resolves the clang-8 error: "unable to make temporary file"?

Question

I am using Windows + Cygwin + Eclipse + LLVM toolchain to build a C/C++ project.

The files compile fine with clang C compiler, but linking with clang++ fails with multiple error: unable to make temporary file: No such file or directory.

clang++ -o test "source1.bc" "source2.bc" "source3.bc" 
clang-8: error: unable to make temporary file: No such file or directory
clang-8: error: unable to make temporary file: No such file or directory
clang-8: error: unable to make temporary file: No such file or directory

Linker generates one error per each object file.

When I add the -save-temps option to linker, it works OK!

What could be the problem?

Adding --verbose gives:

clang version 8.0.1 (tags/RELEASE_801/final) Target: x86_64-unknown-windows-cygnus
Thread model: posix
InstalledDir: /usr/bin
clang-8: error: unable to make temporary file: No such file or directory
clang-8: error: unable to make temporary file: No such file or directory
clang-8: error: unable to make temporary file: No such file or directory

I have checked the TMP and TEMP variables - everything seems OK. I tried changing the TMP and TEMP to include trailing slash /, I also tried the whole path with backslashes \ or forward slashes / - nothing helped.

Here is a more verbose outputs.

First, here is the outputs with flags -save-temps and -###:

 "/usr/bin/clang-8" "-cc1" "-triple" "x86_64-unknown-windows-cygnus" "-S" "-save-temps=cwd" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "my_files\\my_file1.bc" "-mrelocation-model" "pic" "-pic-level" "2" "-mthread-model" "posix" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-dwarf-column-info" "-debugger-tuning=gdb" "-momit-leaf-frame-pointer" "-v" "-resource-dir" "/usr/lib/clang/8.0.1" "-fdebug-compilation-dir" "/cygdrive/c/my_projects/prj1/Debug" "-ferror-limit" "19" "-fmessage-length" "0" "-fobjc-runtime=gcc" "-fseh-exceptions" "-fdiagnostics-show-option" "-o" "my_files\\my_file1.s" "-x" "ir" "my_files\\my_file1.bc" "-faddrsig"

Here is the output without -save-temps, just -###:

 "/usr/bin/clang-8" "-cc1" "-triple" "x86_64-unknown-windows-cygnus" "-emit-obj" "-mrelax-all" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "my_files\\my_file1.bc" "-mrelocation-model" "pic" "-pic-level" "2" "-mthread-model" "posix" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-dwarf-column-info" "-debugger-tuning=gdb" "-momit-leaf-frame-pointer" "-v" "-resource-dir" "/usr/lib/clang/8.0.1" "-fdebug-compilation-dir" "/cygdrive/c/my_projects/prj1/Debug" "-ferror-limit" "19" "-fmessage-length" "0" "-fobjc-runtime=gcc" "-fseh-exceptions" "-fdiagnostics-show-option" "-o" "" "-x" "ir" "my_files\\my_file1.bc" "-faddrsig"

So the "-o" "my_files\\my_file1.s" vs "-o" "" seems to be the difference. Is there an explanation?

Also, some more output with flags -save-temps, -###:

"/usr/bin/ld" "-m" "i386pep" "--wrap" "_Znwm" "--wrap" "_Znam" "--wrap" "_ZnwmRKSt9nothrow_t" "--wrap" "_ZnamRKSt9nothrow_t" "--wrap" "_ZdlPv" "--wrap" "_ZdaPv" "--wrap" "_ZdlPvRKSt9nothrow_t" "--wrap" "_ZdaPvKSt9nothrow_t" "-Bdynamic" "--tsaware" "-o" "myexecutable" "/usr/lib/crt0.o" "/usr/lib/gcc/x86_64-pc-cygwin/10/crtbegin.o" "-LC:/mylibraries" "-L/usr/lib/gcc/x86_64-pc-cygwin/10" "-L/usr/x86_64-pc-cygwin/lib" "-L/usr/lib" "-L/usr/lib/w32api" "my_files\\my_file1.o" "my_files\\my_file2.o" " my_files\\my_file3.o" "-lnaturedsp" "-lgcc_s" "-gcc" "-lcygwin" "-ladvapi32" "-lshell32" "-luser32" "-lkernel32" "/usr/lib/default-manifest.o" "/usr/lib/gcc/x86_64-pc-cygwin/10/crtend.o"

and with only -###:

"/usr/bin/ld" "-m" "i386pep" "--wrap" "_Znwm" "--wrap" "_Znam" "--wrap" "_ZnwmRKSt9nothrow_t" "--wrap" "_ZnamRKSt9nothrow_t" "--wrap" "_ZdlPv" "--wrap" "_ZdaPv" "--wrap" "_ZdlPvRKSt9nothrow_t" "--wrap" "_ZdaPvKSt9nothrow_t" "-Bdynamic" "--tsaware" "-o" "myexecutable" "/usr/lib/crt0.o" "/usr/lib/gcc/x86_64-pc-cygwin/10/crtbegin.o" "-LC:/mylibraries" "-L/usr/lib/gcc/x86_64-pc-cygwin/10" "-L/usr/x86_64-pc-cygwin/lib" "-L/usr/lib" "-L/usr/lib/w32api" "" "" "" "-lnaturedsp" "-lgcc_s" "-lgcc" "-lcygwin" "-ladvapi32" "-lshell32" "-luser32" "-lkernel32" "/usr/lib/default-manifest.o" "/usr/lib/gcc/x86_64-pc-cygwin/10/crtend.o"

So, again "my_files\\my_file1.o" "my_files\\my_file2.o" "my_files\\my_file3.o" are lost and substituted with empty strings "" "" "".

One more thing, as pointed out on the clang mailing list: "Neither the driver option -save-temps nor the linker option --save-temps (driver option -Wl,--save-temps) respects TMP/TEMP/TMPDIR. The temporary files are saved relative to the current working directory..."

So, it's not about temporary directory location.

Answer 1

One potential cause of this failure is the tmp environment variable is assigned to a path that does not exist. (There may be other causes.) The error isn't tripped when the -save-temps argument is passed to clang++.exe because the temporary files are instead written to the current working directory and the branch that uses tmp isn't taken.

You may run into the error unable to make temporary file: invalid argument next. One common cause of that is having quotation marks around the path assigned to tmp. For example, you might have written the following in a Batch file:

REM  This is the quoted, fully-qualified path to this script.
set script_directory=%~dp0:~0,-1%
set script_directory="%script_directory%"

REM  clang++.exe requires a writable temporary directory.
set tmp=%script_directory%

%script_directory%\bin\clang++.exe ^
    my_program.exe ^
   -Xclang -main-file-name %script_directory%\src\main.cpp

In that Batch file, the script directory is quoted so that it won't fail when run from a path that contains spaces. Those quotation marks will cause an error. Don't include them when assigning a value to tmp.