| Issue |
133994
|
| Summary |
[clang/Driver] MacOS issue with SDK include dir auto detection
|
| Labels |
|
| Assignees |
|
| Reporter |
mizvekov
|
Homebrew recently made llvm 20 formula available.
With the clang binary available in that formula, there is trouble when using libc++ and adding the Xcode SDK include dir in the command line.
Simple reproducer:
```C++
#include <vector>
```
Compile with `clang++ -isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include -fsyntax-only test.cc`
Results in:
```
/opt/homebrew/Cellar/llvm/20.1.1/bin/../include/c++/v1/cstdlib:93:5: error: <cstdlib> tried including <stdlib.h> but didn't find libc++'s <stdlib.h> header. This usually means that your header search paths are not configured properly. The header search paths should contain the C++ Standard Library headers before any C Standard Library, and you are probably using compiler flags that make that not be the case.
93 | # error <cstdlib> tried including <stdlib.h> but didn't find libc++'s <stdlib.h> header. \
```
This makes it problematic to build llvm itself from that compiler.
Here is a workaround:
1) Install homebrew versions of zlib, libxml2 and libedit:
`brew install zlib libxml2 libedit`
2) Add the following variables to your cmake invocation:
```
"CMAKE_OSX_SYSROOT": "",
"Backtrace_INCLUDE_DIR": "",
"CMAKE_PREFIX_PATH": "/opt/homebrew/opt/zlib;/opt/homebrew/opt/libxml2;/opt/homebrew/opt/libedit"
```
3) If you are using LLVM_OPTIMIZED_TABLEGEN, then these flags are not automatically forwarded to the NATIVE cross compile target, you have to add the following variable as well:
```
"CROSS_TOOLCHAIN_FLAGS_NATIVE": "-DCMAKE_OSX_SYSROOT= -DBacktrace_INCLUDE_DIR= -DCMAKE_PREFIX_PATH=\"/opt/homebrew/opt/zlib;/opt/homebrew/opt/libxml2;/opt/homebrew/opt/libedit\""
```
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