Commit f9daab0a authored by Fangrui Song's avatar Fangrui Song Committed by Will Deacon
Browse files

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



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: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarFangrui Song <maskray@google.com>
Link: https://github.com/llvm/llvm-project/pull/80255

 [1]
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240206074552.541154-1-maskray@google.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent c0b26c06

arch/arm64/include/asm/jump_label.h

+8 −4
Original line number Diff line number Diff line
@@ -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: