linux-kernel - [PATCH 2/8] LoongArch: Only use -Wa,-mla-* options for !CONFIG_CC_HAS_EXPLICIT

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Message-Id: <20220827175436.156464-3-xry111@xry111.site>
Date:   Sun, 28 Aug 2022 01:54:30 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     loongarch@...ts.linux.dev
Cc:     linux-kernel@...r.kernel.org, WANG Xuerui <kernel@...0n.name>,
        Huacai Chen <chenhuacai@...nel.org>,
        Youling Tang <tangyouling@...ngson.cn>,
        Jinyang He <hejinyang@...ngson.cn>,
        Xi Ruoyao <xry111@...111.site>
Subject: [PATCH 2/8] LoongArch: Only use -Wa,-mla-* options for !CONFIG_CC_HAS_EXPLICIT_RELOCS

If explicit relocation hints is used by the toolchain, -Wa,-mla-*
options will be useless for C code.  Only use them for
!CONFIG_CC_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.

Signed-off-by: Xi Ruoyao <xry111@...111.site>
---
 arch/loongarch/Makefile      | 15 ++++++++++++++-
 arch/loongarch/kernel/head.S | 10 +++++-----
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 415e09bdf31a..bd0ea6623245 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -40,10 +40,23 @@ endif
 
 cflags-y			+= -G0 -pipe -msoft-float
 LDFLAGS_vmlinux			+= -G0 -static -n -nostdlib
+
+ifdef CONFIG_CC_HAS_EXPLICIT_RELOCS
+# GCC may have -mexplicit-relocs off by default if it was built with an old
+# assembler.  But with CONFIG_CC_HAS_EXPLICIT_RELOCS we are sure explicit
+# relocation hints are supported by the assembler, so force it.
+cflags-y			+= -mexplicit-relocs
+else
+# Likewise, disable -mexplicit-relocs if GCC enables by default but the
+# assembler does not support it.
+cflags-y			+= $(call cc-option,-mno-explicit-relocs)
+# With -mno-explicit-relocs, use assembler options to adjust code generation
+# for symbol address.
 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
+KBUILD_CFLAGS_MODULE		+= -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/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