Bug#1125754: clang-21: ROCM_PATH envvar excludes resource directory from device libs search path

[Cordell Bloor]

Package: clang-21
Version: 1:21.1.8-1+b1
Severity: normal
X-Debbugs-Cc: cgmb at debian.org, tflink at tirfa.com, debian-ai at lists.debian.org

Dear Maintainer,

clang-21 does not consider the LLVM 21 resource directory for the ROCm
device libs when ROCM_PATH is defined in the environment, unlike older
versions of LLVM (e.g., clang-17).

Various build systems will search for ROCm and then explicitly set the
ROCM_PATH during their build, which causes their builds to fail even if
the ROCM_PATH is correctly set.

To reproduce this problem consider:

    apt install -y hipcc clang-21 rocm-device-libs-21
    cat > main.hip << END
    int main() { return 0; }
    END
    clang++-21 main.hip -lamdhip64 -o main # SUCCESS
    ROCM_PATH=/usr clang++-21 main.hip -lamdhip64 -o main # FAIL

The failing output (with -v added) is:

    Debian clang version 21.1.8 (1+b1)
    Target: x86_64-pc-linux-gnu
    Thread model: posix
    InstalledDir: /usr/lib/llvm-21/bin
    Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/15
    Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/15
    Candidate multilib: .;@m64
    Selected multilib: .;@m64
    Found HIP installation: /usr, version 6.4.43484
    clang++-21: error: cannot find ROCm device library; provide its path via '--rocm-path' or '--rocm-device-lib-path', or pass '-nogpulib' to build without ROCm device library

To resolve this problem, the LLVM resource directory should always be
considered when searching for the ROCm device libraries.

Sincerely,
Cory Bloor

-- System Information:
Debian Release: forky/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.17.13+deb13-amd64 (SMP w/12 CPU threads; PREEMPT)
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect

Versions of packages clang-21 depends on:
ii  binutils                2.45.50.20251209-1
ii  libc6                   2.42-7
ii  libc6-dev               2.42-7
ii  libclang-common-21-dev  1:21.1.8-1+b1
ii  libclang-cpp21          1:21.1.8-1+b1
ii  libclang1-21            1:21.1.8-1+b1
ii  libgcc-15-dev           15.2.0-12
ii  libgcc-s1               15.2.0-12
ii  libllvm21               1:21.1.8-1+b1
ii  libobjc-15-dev          15.2.0-12
ii  libstdc++-15-dev        15.2.0-12
ii  libstdc++6              15.2.0-12
ii  llvm-21-linker-tools    1:21.1.8-1+b1

Versions of packages clang-21 recommends:
ii  clang-tools-21  1:21.1.8-1+b1
pn  llvm-21-dev     <none>
ii  python3         3.13.9-3

Versions of packages clang-21 suggests:
pn  clang-21-doc  <none>
pn  wasi-libc     <none>

-- no debconf information