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authorXi Ruoyao <xry111@xry111.site>2022-10-12 11:36:08 +0300
committerHuacai Chen <chenhuacai@loongson.cn>2022-10-12 11:36:08 +0300
commit11cd8a648301af0ad6937ed9493519d1e93fd4c8 (patch)
tree019dfcc50e578b49a86867f1ed22350f798144c8 /arch/loongarch
parent0d8dad7048611e5ba02ae8519539ce4b8b1482d3 (diff)
downloadlinux-11cd8a648301af0ad6937ed9493519d1e93fd4c8.tar.xz
LoongArch: Adjust symbol addressing for AS_HAS_EXPLICIT_RELOCS
If explicit relocation hints are used by the toolchain, -Wa,-mla-* options will be useless for the C code. So only use them for the !CONFIG_AS_HAS_EXPLICIT_RELOCS case. 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 near the loading address of main kernel image, but far from the loading address of modules. So we use model("extreme") attibute to tell the compiler that 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 relocs explicit relocs * Behavior ============================================================== No No Use la.* macros. No change from Linux 6.0. -------------------------------------------------------------- No Yes Disable explicit relocs. No change from Linux 6.0. -------------------------------------------------------------- Yes No Not supported. -------------------------------------------------------------- Yes Yes Enable explicit relocs. No -Wa,-mla* options used. ============================================================== *: We assume CC must have model attribute if it has explicit relocs. 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 Tested-by: WANG Xuerui <git@xen0n.name> Signed-off-by: Xi Ruoyao <xry111@xry111.site> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Diffstat (limited to 'arch/loongarch')
-rw-r--r--arch/loongarch/Makefile18
-rw-r--r--arch/loongarch/include/asm/percpu.h9
-rw-r--r--arch/loongarch/kernel/head.S12
-rw-r--r--arch/loongarch/kernel/vmlinux.lds.S4
4 files changed, 37 insertions, 6 deletions
diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 84689c3ee3af..42352f905858 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -43,10 +43,28 @@ 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
+KBUILD_CFLAGS_KERNEL += -mdirect-extern-access
+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..ad8d88494554 100644
--- a/arch/loongarch/include/asm/percpu.h
+++ b/arch/loongarch/include/asm/percpu.h
@@ -8,6 +8,15 @@
#include <asm/cmpxchg.h>
#include <asm/loongarch.h>
+/*
+ * The "address" (in fact, offset from $r21) of a per-CPU variable is close to
+ * the loading address of main kernel image, but far from where the modules are
+ * loaded. Tell the compiler this fact when using explicit relocs.
+ */
+#if defined(MODULE) && defined(CONFIG_AS_HAS_EXPLICIT_RELOCS)
+#define PER_CPU_ATTRIBUTES __attribute__((model("extreme")))
+#endif
+
/* Use r21 for fast access */
register unsigned long __my_cpu_offset __asm__("$r21");
diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
index 7e57ae8741b1..0c67c24ce087 100644
--- a/arch/loongarch/kernel/head.S
+++ b/arch/loongarch/kernel/head.S
@@ -57,19 +57,19 @@ 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
- la t0, fw_arg2
+ la.pcrel t0, fw_arg2
st.d a2, t0, 0
/* KSave3 used for percpu base, initialized as 0 */
@@ -77,7 +77,7 @@ 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
diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S
index e5890bec2bf6..b3309a5e695b 100644
--- a/arch/loongarch/kernel/vmlinux.lds.S
+++ b/arch/loongarch/kernel/vmlinux.lds.S
@@ -55,6 +55,10 @@ SECTIONS
EXCEPTION_TABLE(16)
+ .got : ALIGN(16) { *(.got) }
+ .plt : ALIGN(16) { *(.plt) }
+ .got.plt : ALIGN(16) { *(.got.plt) }
+
. = ALIGN(PECOFF_SEGMENT_ALIGN);
__init_begin = .;
__inittext_begin = .;