e830315641
After commit a35707c3d850 ("riscv: add memory-type errata for T-Head"),
builds with LLVM's integrated assembler fail like:
In file included from arch/riscv/kernel/asm-offsets.c:10:
In file included from ./include/linux/mm.h:29:
In file included from ./include/linux/pgtable.h:6:
In file included from ./arch/riscv/include/asm/pgtable.h:114:
./arch/riscv/include/asm/pgtable-64.h:210:2: error: invalid input constraint '0' in asm
ALT_THEAD_PMA(prot_val);
^
./arch/riscv/include/asm/errata_list.h:88:4: note: expanded from macro 'ALT_THEAD_PMA'
: "0"(_val), \
^
This was reported upstream to LLVM where Jessica pointed out a couple of
issues with the existing implementation of ALT_THEAD_PMA:
* t3 is modified but not listed in the clobbers list.
* "+r"(_val) marks _val as both an input and output of the asm but then
"0"(_val) marks _val as an input matching constraint, which does not
make much sense in this situation, as %1 is not actually used in the
asm and matching constraints are designed to be used for different
inputs that need to use the same register.
Drop the matching contraint and shift all the operands by one, as %1 is
unused, and mark t3 as clobbered. This resolves the build error and goes
not cause any problems with GNU as.
Fixes: a35707c3d850 ("riscv: add memory-type errata for T-Head")
Link: https://github.com/ClangBuiltLinux/linux/issues/1641
Link: https://github.com/llvm/llvm-project/issues/55514
Link: https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html
Suggested-by: Jessica Clarke <jrtc27@jrtc27.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20220518184529.454008-1-nathan@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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.