XCode SDK path changed; clang's sysroot is wrong.

[hv15]

Description

Hi, just today we noticed that when compiling our software on the MacOS image, we get the following warning:
clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk' [-Wmissing-sysroot]. This then leads to errors when trying to compile valid C sources.

Area for Triage:

Apple and XCode

Question, Bug, or Feature?:

Question

Virtual environments affected

• Ubuntu 16.04
• Ubuntu 18.04
• Ubuntu 20.04
• macOS 10.15
• macOS 11.0
• Windows Server 2016 R2
• Windows Server 2019

Expected behavior
We should be able to compile our code fine using Clang.

Actual behavior
When compiling, we get the following error:

clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk' [-Wmissing-sysroot]
In file included from /tmp/SAC_8aZX2e/fun1.c:1:
In file included from /tmp/SAC_8aZX2e/header.h:278:
In file included from /usr/local/include/sac2c/1.3.3-MijasCosta-523-gf6fdf/debug/sac.h:30:
/usr/local/include/sac2c/1.3.3-MijasCosta-523-gf6fdf/debug/runtime/distmem_h/distmem.h:26:10: fatal error: 'stdlib.h' file not found
#include <stdlib.h>
         ^~~~~~~~~~
1 error generated.
abort: System failed to execute shell
abort: command
abort: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc   -march=native -mtune=native  -pedantic -g  -D_DARWIN_C_SOURCE  -fbracket-depth=2048 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -Wall -Wextra -Weverything -Wno-padded -Wno-documentation -Wstrict-prototypes -Wno-unused-parameter -Wno-reserved-id-macro -Wno-shadow -Wno-undef -Wno-conversion -Wno-missing-prototypes -Wno-unused-function -Wno-covered-switch-default -Wno-format-nonliteral -Wno-switch-enum -Wno-missing-noreturn -Wno-float-equal -Wno-vla -Wno-unused-macros -Wno-cast-align -Wno-cast-qual -Wno-documentation-unknown-command -Wno-gnu-zero-variadic-macro-arguments -Wno-alloca -Wno-poison-system-directories -Wno-atomic-implicit-seq-cst -std=gnu99 -pedantic -Wno-unused -fno-builtin  -I.  -DHAVE_CONFIG_H -I/Users/runner/work/Stdlib/build/include -I/Users/runner/work/Stdlib/Stdlib/include -DFULLTYPES -DEXT_STDLIB -DSAC_TARGET_STRING=\"seq\" -DSAC_MODEXT_STRING=\".dylib\" -DSAC_TARGET_ENV_STRING=\"host\" -DSAC_SBI_STRING=\"seq\" -DSAC_RC_METHOD=SAC_RCM_local -DSAC_BACKEND_C99 -DSAC_MT_LIB_ -DSAC_MT_MODE=0 -DSAC_DO_RTSPEC=0 -DSAC_DO_CUDA_ALLOC=SAC_CA_system -DSAC_DO_CUDA_SYNC=1 -I/usr/local/include/sac2c/1.3.3-MijasCosta-523-gf6fdf/debug -c -o /tmp/SAC_8aZX2e/fun1.o /tmp/SAC_8aZX2e/fun1.c
abort: with exit code 1

Repro steps
This affects our repo, see relevant example given through our PR: SacBase/Stdlib#43

The code in this instance doesn't matter, rather our compiler tool (sac2c) which we are using in the above project to compile a standard library, uses a hard-coded path for the sysroot flag. We determine that path when compiling sac2c, which we did on a MacOS 10.15 system (not image). This was about 3 months ago. I think that between then and now some changes (maybe XCode update per #2073) has changed this path.

Is there some generic path we can use instead?

[maxim-lobanov]

Hello @hv15 , default Xcode was changed from 12.0 to 12.2 recently on Hosted images. See #2056
Xcode 12.2 doesn't contain MacOSX10.15.sdk so looks like it causes your failures.

ls -la /Applications/Xcode_12.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs
echo "-----------"
ls -la /Applications/Xcode_12.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs

returns

total 0
drwxr-xr-x  5 runner  wheel  160 Nov 30 22:02 .
drwxr-xr-x  6 runner  wheel  192 Sep 19 01:50 ..
drwxr-xr-x  4 runner  wheel  128 Aug 10 17:36 DriverKit19.0.sdk
drwxr-xr-x  8 runner  wheel  256 Aug 10 17:36 MacOSX.sdk
lrwxr-xr-x  1 runner  wheel   10 Nov 30 21:59 MacOSX10.15.sdk -> MacOSX.sdk
-----------
total 0
drwxr-xr-x  5 runner  wheel  160 Nov 30 23:07 .
drwxr-xr-x  6 runner  wheel  192 Oct 24 02:20 ..
drwxr-xr-x  5 runner  wheel  160 Oct 19 20:33 DriverKit20.0.sdk
drwxr-xr-x  7 runner  wheel  224 Oct 19 20:33 MacOSX.sdk
lrwxr-xr-x  1 runner  wheel   10 Nov 30 23:05 MacOSX11.0.sdk -> MacOSX.sdk

If you still need to use Xcode 12.0, #2056 contains the way to switch Xcode

Update:
In your code you use /Applications/Xcode.app. This path points to default Xcode that can be changed.
I suggest to hardcode some specific Xcode (like 12.0) that works for you.
The paths for all Xcode versions can be found in docs: https://github.com/actions/virtual-environments/blob/main/images/macos/macos-10.15-Readme.md#xcode

[hv15]

Hi @maxim-lobanov, thanks for the quick reply. I didn't realise one could switch the Xcode version, excellent!

In your code you use /Applications/Xcode.app. This path points to default Xcode that can be changed.
I suggest to hardcode some specific Xcode (like 12.0) that works for you.
The paths for all Xcode versions can be found in docs: https://github.com/actions/virtual-environments/blob/main/images/macos/macos-10.15-Readme.md#xcode

Spot on, just working to fix that!!! Thanks for your help!

[tangobravo62]

The same problem resurfaces again after switching to OS X 11.1 and XCode 12.3. The SDK now is MacOSX11.1.sdk, but clang requests MacOSX11.0.sdk. Workaround is to create a symlink:

user@localhost ~ % ll /Library/Developer/CommandLineTools/SDKs
total 0
lrwxr-xr-x  1 root  wheel   14 20 Jan 18:24 MacOSX.sdk -> MacOSX11.1.sdk
drwxr-xr-x  8 root  wheel  256  9 Jul  2020 MacOSX10.15.sdk
lrwxr-xr-x  1 root  wheel   55 20 Jan 18:34 MacOSX11.0.sdk -> /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk
drwxr-xr-x  7 root  wheel  224 30 Nov 13:33 MacOSX11.1.sdk

A better solution would be to not request a specific version of the Mac OS SDK at all, but the generic MacOSX.sdk, which will – given a correct installation of XCode and XCode Command Line Tools – always point to the current version of the SDK.