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Nathan Chancellor e89c2e815e
 riscv: Handle zicsr/zifencei issues between clang and binutils 
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 6df2a016c0 ("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'.

[1]: 22e199e6af
[2]: https://lore.kernel.org/ZAxT7T9Xy1Fo3d5W@aurel32.net/

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>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230313-riscv-zicsr-zifencei-fiasco-v1-1-dd1b7840a551@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
History 2023-03-23 12:52:49 -07:00
arch riscv: Handle zicsr/zifencei issues between clang and binutils 2023-03-23 12:52:49 -07:00
block block-6.3-2023-03-03 2023-03-03 10:21:39 -08:00
certs Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
crypto Networking changes for 6.3. 2023-02-21 18:24:12 -08:00
Documentation A small set of updates for x86: 2023-03-05 11:27:48 -08:00
drivers This push fixes a regression in the caam driver. 2023-03-05 11:32:30 -08:00
fs 17 hotfixes. Eight are for MM and seven are for other parts of the 2023-03-04 13:32:50 -08:00
include cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
init Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
io_uring io_uring-6.3-2023-03-03 2023-03-03 10:25:29 -08:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel A set of updates for the interrupt susbsystem: 2023-03-05 11:19:16 -08:00
lib cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: avoid gcc complaint about pointer casting 2023-03-04 14:03:27 -08:00
net nfsd-6.3 fixes: 2023-03-01 11:03:44 -08:00
rust Rust fixes for 6.3-rc1 2023-03-03 14:51:15 -08:00
samples LoongArch changes for v6.3 2023-03-01 09:27:00 -08:00
scripts Remove Intel compiler support 2023-03-05 10:49:37 -08:00
security capability: just use a 'u64' instead of a 'u32[2]' array 2023-03-01 10:01:22 -08:00
sound sound fixes for 6.3-rc1 2023-03-04 10:53:59 -08:00
tools Changes in this cycle were: 2023-03-02 09:45:34 -08:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM/riscv changes for 6.3 2023-02-15 12:33:28 -05:00
.clang-format cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore .gitignore: ignore *.cover and *.mbx 2023-02-05 18:51:22 +09:00
.mailmap mailmap: map Dikshita Agarwal's old address to his current one 2023-03-02 21:54:24 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS There is no particular theme here - mainly quick hits all over the tree. 2023-02-23 17:55:40 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Adding Christian Brauner as VFS co-maintainer. 2023-03-05 11:11:52 -08:00
Makefile Linux 6.3-rc1 2023-03-05 14:52:03 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.