Hey Nathan,
On Mon, Mar 13, 2023 at 04:00:23PM -0700, Nathan Chancellor wrote:
There are two related issues that appear in certain combinations with clang and GNU binutils.
The first occurs when a version of clang that supports zicsr or zifencei via '-march=' [1] (i.e, >= 17.x) is used in combination with a version of GNU binutils that do not recognize zicsr and zifencei in the '-march=' value (i.e., < 2.36):
riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei' riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/file.o riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zicsr2p0_zifencei2p0: Invalid or unknown z ISA extension: 'zifencei' riscv64-linux-gnu-ld: failed to merge target specific data of file fs/efivarfs/super.o
The second occurs when a version of clang that does not support zicsr or zifencei via '-march=' (i.e., <= 16.x) is used in combination with a version of GNU as that defaults to a newer ISA base spec, which requires specifying zicsr and zifencei in the '-march=' value explicitly (i.e, >= 2.38):
../arch/riscv/kernel/kexec_relocate.S: Assembler messages: ../arch/riscv/kernel/kexec_relocate.S:147: Error: unrecognized opcode `fence.i', extension `zifencei' required clang-12: error: assembler command failed with exit code 1 (use -v to see invocation)
This is the same issue addressed by commit 6df2a016c0c8 ("riscv: fix build with binutils 2.38") (see [2] for additional information) but older versions of clang miss out on it because the cc-option check fails:
clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr' clang-12: error: invalid arch name 'rv64imac_zicsr_zifencei', unsupported standard user-level extension 'zicsr'
To resolve the first issue, only attempt to add zicsr and zifencei to the march string when using the GNU assembler 2.38 or newer, which is when the default ISA spec was updated, requiring these extensions to be specified explicitly. LLVM implements an older version of the base specification for all currently released versions, so these instructions are available as part of the 'i' extension. If LLVM's implementation is updated in the future, a CONFIG_AS_IS_LLVM condition can be added to CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI.
To resolve the second issue, use version 2.2 of the base ISA spec when using an older version of clang that does not support zicsr or zifencei via '-march=', as that is the spec version most compatible with the one clang/LLVM implements and avoids the need to specify zicsr and zifencei explicitly due to still being a part of 'i'.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1808 Co-developed-by: Conor Dooley conor.dooley@microchip.com Signed-off-by: Conor Dooley conor.dooley@microchip.com
TBH, barely identifiable as having much to do with my V1 anymore, so could easily have dropped those. Either way, thanks for sorting this out while I've been sick :)
Acked-by: Conor Dooley conor.dooley@microchip.com
Signed-off-by: Nathan Chancellor nathan@kernel.org
This is essentially a v3 of Conor's v1 and v2 but since I am sending the patch after finding a separate but related issue, I left it at v1:
- v1: https://lore.kernel.org/20230223220546.52879-1-conor@kernel.org/
- v2: https://lore.kernel.org/20230308220842.1231003-1-conor@kernel.org/
I have built allmodconfig with the following toolchain combinations to confirm this problem is resolved:
- clang 12/17 + GNU as and ld 2.35/2.39
- clang 12/17 with the integrated assembler + GNU ld 2.35/2.39
- clang 12/17 with the integrated assembler + ld.lld
There are a couple of other incompatibilities between clang-17 and GNU binutils that I had to patch to get allmodconfig to build successfully but those are less likely to be hit in practice because the full LLVM stack can be used with LLVM versions 13.x and newer.
I will follow up with separate issues and patches.
Cool, I'll "look forward" to those...
Thanks, Conor.