[clang][main] Does not detect embed gcc toolchain

Clang Frontend
1

Hello,

I’m building clang main, revision b785e03612d76145c58cb31b6fd6911a5e41e8e3, and I’m adding to lib folder gcc toolchain 7.4.0, so the folder layout is:

clang/lib/gcc/x86_64-unknown-linux-gnu/7.4.0

Unfortunately when I want to build on linux debian and I do a verbose build clang doesn’t seem able to find the gcc version that I’ve shipped it with:

clang version 13.0.0 (E4V8ZoJsR3qTRv_zx8MEpA)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/someuser/clang/clang/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9

Candidate multilib: .;@m64
Selected multilib: .;@m64

Doing the same thing but building the official clang 11.0.1 I’m seeing normal results:

clang version 11.0.1 (NZ4C_ZaZTQmrQM25NeOO0Q)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/someuser/mozilla/clang/clang-11/clang/bin
Found candidate GCC installation: /home/someuser/clang/clang-11/clang/bin/…/lib/gcc/x86_64-unknown-linux-gnu/7.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.2
Selected GCC installation: /home/someuser/clang/clang-11/clang/bin/…/lib/gcc/x86_64-unknown-linux-gnu/7.4.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

Has anyone confronted with this lately?

Many thanks

2

Ray - I think you've been doing some work related to toolchain
discovery stuff recently, might this be related?

3

The GCC installation detection logic is in Generic_GCC::GCCInstallationDetector::init.

If --sysroot is not empty (or unspecified and cmake DEFAULT_SYSROOT is not empty), the search order is: $sysroot/usr $sysroot dir(clang)/..
otherwise dir(clang)/.. $sysroot/usr $sysroot

Before 13.0.0 Clang picked the search directory with the largest GCC
version. This made the behavior less predictable, e.g. if your system
version is larger than 7.4.0, you would end up with the system gcc.

The new behavior stops at the first search directory with a GCC installation.
In your case, instead of relying on dir(clang)/.. (the behavior may be
questionable), specifying --gcc-toolchain=/home/someuser/clang/clang-11/clang
is more robost (if you can find lib/gcc{,-cross}/$triple in that directory).