Messages in this thread Patch in this message | | | From | Xi Ruoyao <> | Subject | [PATCH 6/8] LoongArch: Use model("extreme") attribute for per-CPU variables in module if CONFIG_CC_HAS_EXPLICIT_RELOCS | Date | Sun, 28 Aug 2022 01:54:34 +0800 |
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On LoongArch, The "address" of a per-CPU variable symbol is actually an offset from $r21. The value is nearing the loading address of main kernel image, but far from the address of modules. We need to tell the compiler that a PC-relative addressing with 32-bit offset is not sufficient for local per-CPU variables.
After some discussion with GCC maintainers, we implemented this attribute to indicate that a PC-relative addressing with 64-bit offset should be used.
This attribute should be available in GCC 13 release. Some early GCC 13 snapshots may support -mexplicit-relocs but lack this attribute, we simply reject them.
Link: https://gcc.gnu.org/r13-2199 Signed-off-by: Xi Ruoyao <xry111@xry111.site> --- arch/loongarch/include/asm/percpu.h | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h index 0bd6b0110198..91d4026b074e 100644 --- a/arch/loongarch/include/asm/percpu.h +++ b/arch/loongarch/include/asm/percpu.h @@ -8,6 +8,19 @@ #include <asm/cmpxchg.h> #include <asm/loongarch.h> +#if defined(MODULE) && defined(CONFIG_CC_HAS_EXPLICIT_RELOCS) +# if __has_attribute(model) +/* The "address" (in fact, offset from $r21) of a per-CPU variable is close + * to the load address of main kernel image, but far from where the modules are + * loaded. Tell the compiler this fact. + */ +# define PER_CPU_ATTRIBUTES __attribute__((model("extreme"))) +# else /* __has_attribute(model) */ +/* This should only happen with early GCC 13 snapshots. */ +# error "Compiler with explicit relocs but no model attribute is not supported" +# endif /* __has_attribute(model) */ +#endif + /* Use r21 for fast access */ register unsigned long __my_cpu_offset __asm__("$r21"); -- 2.37.0
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