Re: [PATCH v10 2/2] riscv: Add runtime constant support
From: Nathan Chancellor <nathan@kernel.org>
Date: 2025-04-01 19:28:40
Also in:
linux-riscv, lkml, llvm
Hi Charlie, On Wed, Mar 19, 2025 at 11:35:20AM -0700, Charlie Jenkins wrote:
Implement the runtime constant infrastructure for riscv. Use this
infrastructure to generate constants to be used by the d_hash()
function.
This is the riscv variant of commit 94a2bc0f611c ("arm64: add 'runtime
constant' support") and commit e3c92e81711d ("runtime constants: add
x86 architecture support").
Signed-off-by: Charlie Jenkins <redacted>
Reviewed-by: Alexandre Ghiti <redacted>...
quoted hunk ↗ jump to hunk
diff --git a/arch/riscv/include/asm/runtime-const.h b/arch/riscv/include/asm/runtime-const.h
...
+#define RISCV_RUNTIME_CONST_64_ZBA \ + ".option push\n\t" \ + ".option arch,+zba\n\t" \ + "slli %[__tmp],%[__tmp],32\n\t" \ + "add.uw %[__ret],%[__ret],%[__tmp]\n\t" \ + "nop\n\t" \ + "nop\n\t" \ + ".option pop\n\t" \
...
+#if defined(CONFIG_RISCV_ISA_ZBA) && defined(CONFIG_RISCV_ISA_ZBKB)
...
+#elif defined(CONFIG_RISCV_ISA_ZBA)
+#define runtime_const_ptr(sym) \
+({ \
+ typeof(sym) __ret, __tmp; \
+ asm_inline(RISCV_RUNTIME_CONST_64_PREAMBLE \
+ ALTERNATIVE( \
+ RISCV_RUNTIME_CONST_64_BASE, \
+ RISCV_RUNTIME_CONST_64_ZBA, \
+ 0, RISCV_ISA_EXT_ZBA, 1 \
+ ) \
+ RISCV_RUNTIME_CONST_64_POSTAMBLE(sym) \
+ : [__ret] "=r" (__ret), [__tmp] "=r" (__tmp)); \
+ __ret; \
+})
This breaks the build for clang versions 16 and earlier because they do
not support '.option arch' and it is used in CONFIG_RISCV_ISA_ZBA, which
has no dependencies and it is default on.
$ make -skj"$(nproc)" ARCH=riscv LLVM=1 mrproper defconfig fs/dcache.o
fs/dcache.c:117:9: warning: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'relax' or 'norelax' [-Winline-asm]
return runtime_const_ptr(dentry_hashtable) +
^
arch/riscv/include/asm/runtime-const.h:103:4: note: expanded from macro 'runtime_const_ptr'
RISCV_RUNTIME_CONST_64_ZBA, \
^
arch/riscv/include/asm/runtime-const.h:57:17: note: expanded from macro 'RISCV_RUNTIME_CONST_64_ZBA'
".option push\n\t" \
^
<inline asm>:32:10: note: instantiated into assembly here
.option arch,+zba
^
fs/dcache.c:117:9: error: instruction requires the following: 'Zba' (Address Generation Instructions)
return runtime_const_ptr(dentry_hashtable) +
^
arch/riscv/include/asm/runtime-const.h:103:4: note: expanded from macro 'runtime_const_ptr'
RISCV_RUNTIME_CONST_64_ZBA, \
^
arch/riscv/include/asm/runtime-const.h:59:30: note: expanded from macro 'RISCV_RUNTIME_CONST_64_ZBA'
"slli %[__tmp],%[__tmp],32\n\t" \
^
<inline asm>:34:2: note: instantiated into assembly here
add.uw a2,a2,a3
^
...
$ rg 'OPTION_ARCH|ZBA' .config
364:CONFIG_RISCV_ISA_ZBA=y
Should it grow a dependency on AS_HAS_OPTION_ARCH or should there be a
different fix?
Cheers,
Nathan