On Thu, Feb 29, 2024 at 10:49:26AM -0500, Sasha Levin wrote:
From: Fangrui Song maskray@google.com
[ Upstream commit f9daab0ad01cf9d165dbbbf106ca4e61d06e7fe8 ]
Please drop this; same story as wit the v6.7 backport:
https://lore.kernel.org/lkml/ZeCpOPDi18OBEclz@FVFF77S0Q05N/
Mark.
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 Signed-off-by: Sasha Levin sashal@kernel.org
arch/arm64/include/asm/jump_label.h | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h index 48ddc0f45d228..b7716b215f91a 100644 --- a/arch/arm64/include/asm/jump_label.h +++ b/arch/arm64/include/asm/jump_label.h @@ -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"
: : "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"
: : "i"(&((char *)key)[branch]) : : l_yes);
: : [key]"Si"(key), [bit0]"i"(branch) : : l_yes);return false; l_yes: -- 2.43.0