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arm64: jump_label: use constraints "Si" instead of "i"

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The generic constraint "i" seems to be copied from x86 or arm (and with
a redundant generic operand modifier "c"). It works with -fno-PIE but
not with -fPIE/-fPIC in GCC's aarch64 port.

The machine constraint "S", which denotes a symbol or label reference
with a constant offset, supports PIC and has been available in GCC since
2012 and in Clang since 7.0. However, Clang before 19 does not support
"S" on a symbol with a constant offset [1] (e.g.
`static_key_false(&nf_hooks_needed[pf][hook])` in
include/linux/netfilter.h), so we use "i" as a fallback.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Fangrui Song <maskray@google.com>
Link: https://github.com/llvm/llvm-project/pull/80255 [1]
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240206074552.541154-1-maskray@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Fangrui Song 2024-02-05 23:45:52 -08:00 committed by Will Deacon
parent c0b26c06ed
commit f9daab0ad0
1 changed files with 8 additions and 4 deletions
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12
arch/arm64/include/asm/jump_label.h
View file

@ -15,6 +15,10 @@
#define JUMP_LABEL_NOP_SIZE AARCH64_INSN_SIZE
/*
* Prefer the constraint "S" to support PIC with GCC. Clang before 19 does not
* support "S" on a symbol with a constant offset, so we use "i" as a fallback.
*/
static __always_inline bool arch_static_branch(struct static_key * const key,
const bool branch)
{
@ -23,9 +27,9 @@ static __always_inline bool arch_static_branch(struct static_key * const key,
" .pushsection __jump_table, \"aw\" \n\t"
" .align 3 \n\t"
" .long 1b - ., %l[l_yes] - . \n\t"
" .quad %c0 - . \n\t"
" .quad (%[key] - .) + %[bit0] \n\t"
" .popsection \n\t"
: : "i"(&((char *)key)[branch]) : : l_yes);
: : [key]"Si"(key), [bit0]"i"(branch) : : l_yes);
return false;
l_yes:
@ -40,9 +44,9 @@ static __always_inline bool arch_static_branch_jump(struct static_key * const ke
" .pushsection __jump_table, \"aw\" \n\t"
" .align 3 \n\t"
" .long 1b - ., %l[l_yes] - . \n\t"
" .quad %c0 - . \n\t"
" .quad (%[key] - .) + %[bit0] \n\t"
" .popsection \n\t"
: : "i"(&((char *)key)[branch]) : : l_yes);
: : [key]"Si"(key), [bit0]"i"(branch) : : l_yes);
return false;
l_yes: