Messages in this thread Patch in this message | | | From | Xi Ruoyao <> | Subject | [PATCH v7 2/5] LoongArch: Adjust symbol addressing for CONFIG_AS_HAS_EXPLICIT_RELOCS | Date | Tue, 30 Aug 2022 18:48:03 +0800 |
| |
If explicit relocation hints is used by the toolchain, -Wa,-mla-* options will be useless for C code. Only use them for !CONFIG_AS_HAS_EXPLICIT_RELOCS.
Replace "la" with "la.pcrel" in head.S to keep the semantic consistent with new and old toolchains for the low level startup code.
For per-CPU variables, the "address" of the 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. Use model("extreme") attibute to tell the compiler that a a PC-relative addressing with 32-bit offset is not sufficient for local per-CPU variables.
The behavior with different assemblers and compilers are summarized in the following table:
AS has CC has explicit reloc explicit reloc * Behavior ============================================================== No No Use la.* macros. No change from Linux 6.0. -------------------------------------------------------------- No Yes Disable explicit reloc. No change from Linux 6.0. -------------------------------------------------------------- Yes No Not supported. -------------------------------------------------------------- Yes Yes Use explicit relocs. No -Wa,-mla* options. ============================================================== *: We assume CC must have model attribute if it has explicit reloc. Both features are added in GCC 13 development cycle, so any GCC release >= 13 should be OK. Using early GCC 13 development snapshots may produce modules with unsupported relocations.
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=f09482a Link: https://gcc.gnu.org/r13-1834 Link: https://gcc.gnu.org/r13-2199 Signed-off-by: Xi Ruoyao <xry111@xry111.site> --- arch/loongarch/Makefile | 17 +++++++++++++++++ arch/loongarch/include/asm/percpu.h | 8 ++++++++ arch/loongarch/kernel/head.S | 10 +++++----- 3 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile index 7051a95f7f31..92c4a52c4c3e 100644 --- a/arch/loongarch/Makefile +++ b/arch/loongarch/Makefile @@ -40,10 +40,27 @@ endif cflags-y += -G0 -pipe -msoft-float LDFLAGS_vmlinux += -G0 -static -n -nostdlib + +# When the assembler supports explicit relocation hint, we must use it. +# GCC may have -mexplicit-relocs off by default if it was built with an old +# assembler, so we force it via an option. +# +# When the assembler does not supports explicit relocation hint, we can't use +# it. Disable it if the compiler supports it. +# +# If you've seen "unknown reloc hint" message building the kernel and you are +# now wondering why "-mexplicit-relocs" is not wrapped with cc-option: the +# combination of a "new" assembler and "old" compiler is not supported. Either +# upgrade the compiler or downgrade the assembler. +ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS +cflags-y += -mexplicit-relocs +else +cflags-y += $(call cc-option,-mno-explicit-relocs) KBUILD_AFLAGS_KERNEL += -Wa,-mla-global-with-pcrel KBUILD_CFLAGS_KERNEL += -Wa,-mla-global-with-pcrel KBUILD_AFLAGS_MODULE += -Wa,-mla-global-with-abs KBUILD_CFLAGS_MODULE += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs +endif cflags-y += -ffreestanding cflags-y += $(call cc-option, -mno-check-zero-division) diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h index 0bd6b0110198..dd7fcc553efa 100644 --- a/arch/loongarch/include/asm/percpu.h +++ b/arch/loongarch/include/asm/percpu.h @@ -8,6 +8,14 @@ #include <asm/cmpxchg.h> #include <asm/loongarch.h> +#if defined(MODULE) && defined(CONFIG_AS_HAS_EXPLICIT_RELOCS) +/* The "address" (in fact, offset from $r21) of a per-CPU variable is close + * to the load address of main kernel image, but far from where the modules are + * loaded. Tell the compiler this fact. + */ +# define PER_CPU_ATTRIBUTES __attribute__((model("extreme"))) +#endif + /* Use r21 for fast access */ register unsigned long __my_cpu_offset __asm__("$r21"); diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S index 01bac62a6442..eb3f641d5915 100644 --- a/arch/loongarch/kernel/head.S +++ b/arch/loongarch/kernel/head.S @@ -55,17 +55,17 @@ SYM_CODE_START(kernel_entry) # kernel entry point li.w t0, 0x00 # FPE=0, SXE=0, ASXE=0, BTE=0 csrwr t0, LOONGARCH_CSR_EUEN - la t0, __bss_start # clear .bss + la.pcrel t0, __bss_start # clear .bss st.d zero, t0, 0 - la t1, __bss_stop - LONGSIZE + la.pcrel t1, __bss_stop - LONGSIZE 1: addi.d t0, t0, LONGSIZE st.d zero, t0, 0 bne t0, t1, 1b - la t0, fw_arg0 + la.pcrel t0, fw_arg0 st.d a0, t0, 0 # firmware arguments - la t0, fw_arg1 + la.pcrel t0, fw_arg1 st.d a1, t0, 0 /* KSave3 used for percpu base, initialized as 0 */ @@ -73,7 +73,7 @@ SYM_CODE_START(kernel_entry) # kernel entry point /* GPR21 used for percpu base (runtime), initialized as 0 */ move u0, zero - la tp, init_thread_union + la.pcrel tp, init_thread_union /* Set the SP after an empty pt_regs. */ PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE) PTR_ADD sp, sp, tp -- 2.37.0
| |