The two scenarios described within where splicing doesn't handle
selecting the right package for us are observable in the following
(nix repl session):
```
> np = import <nixpkgs> { system = "x86_64-linux"; crossSystem = { config = "aarch64-linux"; }; }
> np.__splicedPackages.hello ? __spliced
true
> np.__splicedPackages.python3Packages.psutil ? __spliced
true
> np.__splicedPackages.python3.pkgs.psutil ? __spliced
false
> (np.__splicedPackages.python3.withPackages (ps: with ps; [psutil])) ? __spliced
false
```
See: #211340
Details within but ultimately there isn't a satisfying resolution for
any of the three test failures we were seeing and all three deserve
further exploration.
For the `sw_vers` macOS version issue in particular, it's possible to
observe the nixpkgs provided `CoreFoundation` vs system `CoreFoundation`
for `x86_64` and `aarch64` like so (on a host running macOS `13.0.1`):
```console
$ nix-shell -p darwin.DarwinTools --system aarch64-darwin --command "sw_vers"
ProductName: macOS
ProductVersion: 13.0.1
BuildVersion: 22A400
$ nix-shell -p darwin.DarwinTools --system x86_64-darwin --command "sw_vers"
ProductName: Mac OS X
ProductVersion: 10.16
BuildVersion: 22A400
```
Where `/System/Library/CoreServices/SystemVersion.plist` has:
```console
$ cat /System/Library/CoreServices/SystemVersion.plist | grep ProductVersion
-A 1
<key>ProductVersion</key>
<string>13.0.1</string>
```
Further:
```console
$ nix-shell -p darwin.DarwinTools --system aarch64-darwin --command 'otool -L $(which sw_vers)'
/nix/store/nb2q33ak2zif49ndcpc6m823z0vhmy8y-DarwinTools-1/bin/sw_vers:
/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1770.255.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1292.60.1)
$ nix-shell -p darwin.DarwinTools --system x86_64-darwin --command 'otool -L $(which sw_vers)'
/nix/store/88v4kjvgwl71byfpvd0baviiq7l5appc-DarwinTools-1/bin/sw_vers:
@rpath/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1454.90.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
```
For the `x86_64` `sw_vers` binary we can see rpath:
```console
$ nix-shell -p darwin.DarwinTools --system x86_64-darwin --command 'otool -l $(which sw_vers)' | grep LC_RPATH -A 2 -B 1
Load command 13
cmd LC_RPATH
cmdsize 120
path /nix/store/zvr4wypbgskhhw9cawfn7mmxfa75nh8f-swift-corefoundation-unstable-2018-09-14/Library/Frameworks (offset 12)
```
And we can confirm that the nixpkgs provided `CoreFoundation` is what
ultimately gets loaded:
```console
$ nix-shell -p darwin.DarwinTools --system x86_64-darwin --command 'DYLD_PRINT_LIBRARIES=1 sw_vers'
dyld[16215]: <no uuid> /nix/store/88v4kjvgwl71byfpvd0baviiq7l5appc-DarwinTools-1/bin/sw_vers
dyld[16215]: <no uuid> /nix/store/zvr4wypbgskhhw9cawfn7mmxfa75nh8f-swift-corefoundation-unstable-2018-09-14/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation
dyld[16215]: <no uuid> /nix/store/xd2a4xh8kdwq0j67hzgw720npdw5hzkk-ICU-66108/lib/libicucore.A.dylib
<snipped>
```
```bash
nix-diff \
$(nix path-info nixpkgs#legacyPackages.aarch64-darwin.darwin.DarwinTools --derivation) \
$(nix path-info nixpkgs#legacyPackages.x86_64-darwin.darwin.DarwinTools --derivation)
```
doesn't show any _obvious_ discrepancies
there are a few parts to this:
- adding darwin specific check deps
- working around referencing LLVM dylibs during the checkPhase in a
way that supports darwin
+ previously we just set `$LD_LIBRARY_PATH` and/or made some
strategic symlinks
+ now we have LLVM's `lit` config set the appropriate env vars as
needed (as is done for other LLVM subprojects)
+ in retrospect switching to `installCheckPhase` might have been the
better move..
- patching `lit` to deal with `$DYLD_LIBRARY_PATH` being purged for
new "protected" processes
more details within.
as detailed within, adding `asm/ptrace.h` leads to `asm/ptrace-abi.h`
being included which defines preprocessor symbols that clash with
identifiers used in the LLVM headers (`FS` and `CS` only defined on
i686)
This restores this check to what it originally was in #196909 (see:
https://github.com/NixOS/nixpkgs/pull/196909#discussion_r1000536298) and
lets `compiler-rt` eval successfully when trying to compile the
`llvmPackages_15` set for mingw targets (i.e. a platform that *is* GNU
but does *not* use glibc).
---
It's not clear to me what the `haveLibc` check is doing here (platforms
that seem to use glibc like `x86_64-linux` and have
`plat.libc == "glibc"` have `haveLibc = false` because `stdenv.cc.libc`
is `null`).
libc++ has switched to using `__attribute__((using_if_exists))` to handle
incomplete libc implementations; see: a9c9183ca4
These essentially require a modern C++ compiler (clang gained support in
LLVM 13: 369c648399,
gcc appears to not have support yet: https://gcc.gnu.org/bugzilla//show_bug.cgi?id=105584).
Previously this was not an issue for us (despite the transition happening
around LLVM 13) but something about the changes to the libc++/libc++-abi
build has made it so that on platforms with incomplete libc impls (i.e.
Darwin is missing `quick_exit`/`at_quick_exit`) we error during the `libcxx-abi`
build when the stdenv's (older, not supporting `using_if_exists`) compiler
tries to import libc symbols that aren't present.
The libc++ docs suggest we use a modern compiler to build libc++ anyways
(https://releases.llvm.org/15.0.0/projects/libcxx/docs/index.html#platform-and-compiler-support)
so this commit uses stdenv's containing the package set's clang to build
libcxx/libcxx-abi.
This is similar to how libc++ bootstrapping builds (https://releases.llvm.org/15.0.0/projects/libcxx/docs/BuildingLibcxx.html#bootstrapping-build)
work.
None of the patches required any touch-up; the only change of note is:
- due to changes in the libc++/libc++abi build
(https://reviews.llvm.org/D120719 and https://reviews.llvm.org/D131037)
we have to add an extra build option to the libc++ header only
build that sidesteps bits of the libc++ build config that assume
libc++-abi is present in the build:
4f827318e3/libcxx/src/CMakeLists.txt (L255-L256)
Rather than maintaining a precise set of build options that let us dodge
referencing libc++-abi variables in the libc++ header only build, we set
`LIBCXX_CXX_ABI` to `none`, as suggested by @lovesegfault.
More discussion about this here: https://github.com/NixOS/nixpkgs/pull/194634#discussion_r990267037
Co-authored-by: Bernardo Meurer <bernardo@meurer.org>
