5fe41793bc
Nathan reports that the new get_current() and per-CPU offset accessors
may cause problems at build time due to the use of a literal to hold the
address of the respective variables. This is due to the fact that LLD
before v14 does not support the PC-relative group relocations that are
normally used for this, and the fallback relies on literals but does not
emit the literal pools explictly using the .ltorg directive.
./arch/arm/include/asm/current.h:53:6: error: out of range pc-relative fixup value
asm(LOAD_SYM_ARMV6(%0, __current) : "=r"(cur));
^
./arch/arm/include/asm/insn.h:25:2: note: expanded from macro 'LOAD_SYM_ARMV6'
" ldr " #reg ", =" #sym " nt"
^
<inline asm>:1:3: note: instantiated into assembly here
ldr r0, =__current
^
Since emitting a literal pool in this particular case is not possible,
let's avoid the LOAD_SYM_ARMV6() entirely, and use the ordinary C
assigment instead.
As it turns out, there are other such cases, and here, using .ltorg to
emit the literal pool within range of the LDR instruction would be
possible due to the presence of an unconditional branch right after it.
Unfortunately, putting .ltorg directives in subsections appears to
confuse the Clang inline assembler, resulting in similar errors even
though the .ltorg is most definitely within range.
So let's fix this by emitting the literal explicitly, and not rely on
the assembler to figure this out. This means we have move the fallback
out of the LOAD_SYM_ARMV6() macro and into the callers.
Link: https://github.com/ClangBuiltLinux/linux/issues/1551
Fixes: 9c46929e7989 ("ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
48 lines
1.3 KiB
C
48 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_ARM_INSN_H
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#define __ASM_ARM_INSN_H
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#include <linux/types.h>
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/*
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* Avoid a literal load by emitting a sequence of ADD/LDR instructions with the
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* appropriate relocations. The combined sequence has a range of -/+ 256 MiB,
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* which should be sufficient for the core kernel as well as modules loaded
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* into the module region. (Not supported by LLD before release 14)
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*/
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#define LOAD_SYM_ARMV6(reg, sym) \
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" .globl " #sym " \n\t" \
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" .reloc 10f, R_ARM_ALU_PC_G0_NC, " #sym " \n\t" \
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" .reloc 11f, R_ARM_ALU_PC_G1_NC, " #sym " \n\t" \
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" .reloc 12f, R_ARM_LDR_PC_G2, " #sym " \n\t" \
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"10: sub " #reg ", pc, #8 \n\t" \
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"11: sub " #reg ", " #reg ", #4 \n\t" \
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"12: ldr " #reg ", [" #reg ", #0] \n\t"
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static inline unsigned long
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arm_gen_nop(void)
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{
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#ifdef CONFIG_THUMB2_KERNEL
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return 0xf3af8000; /* nop.w */
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#else
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return 0xe1a00000; /* mov r0, r0 */
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#endif
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}
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unsigned long
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__arm_gen_branch(unsigned long pc, unsigned long addr, bool link, bool warn);
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static inline unsigned long
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arm_gen_branch(unsigned long pc, unsigned long addr)
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{
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return __arm_gen_branch(pc, addr, false, true);
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}
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static inline unsigned long
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arm_gen_branch_link(unsigned long pc, unsigned long addr, bool warn)
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{
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return __arm_gen_branch(pc, addr, true, warn);
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}
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#endif
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