linux-kernel - [PATCH v3 3/4] LoongArch: Remove -fplt and -Wa,-mla-* from CFLAGS

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Message-ID: <4da7ce6a6e5b6d609c37ebf6815caacc3b3b8297.camel@xry111.site>
Date:   Fri, 29 Jul 2022 10:09:51 +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>
Subject: [PATCH v3 3/4] LoongArch: Remove -fplt and -Wa,-mla-* from CFLAGS

-fplt is the default of all supported compilers (GCC, and maybe Clang in
the future), so it needs not to be explicitly specified.

-Wa,-mla-* options were used to prevent the assembler from generating
GOT accesses for "la.local" and "la.global" macros.  But GCC >= 13 will
generate GOT access explicitly without use of these macros, so these
options are ineffective for symbol addressing in C code with GCC >= 13.
Now we can handle GOT and GOT-based relocations properly, so we can
remove these options and use GOT access for both GCC 12 and 13
(or newer).

GAS <= 2.39 does not support "la.got [reg], [sym] + [offset]" with a
non-zero offset.  So in the assembly code we explicitly use "la.pcrel"
instead of "la" (now defaulted to "la.got") where a PC-relative
addressing is suitable, in order to work around this limitation and keep
the compatibility with old toolchains.

Signed-off-by: Xi Ruoyao <xry111@...111.site>
---
 arch/loongarch/Makefile      |  4 ----
 arch/loongarch/kernel/head.S | 10 +++++-----
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
index 039dcc4fe1f3..800349ea9310 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -40,10 +40,6 @@ endif
 
 cflags-y			+= -G0 -pipe -msoft-float
 LDFLAGS_vmlinux			+= -G0 -static -n -nostdlib
-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
 
 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 74ea7bf6c8d6..193329ed6e8c 100644
--- a/arch/loongarch/kernel/head.S
+++ b/arch/loongarch/kernel/head.S
@@ -60,17 +60,17 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
 	la.abs		t0, 0f
 	jirl		zero, t0, 0
 0:
-	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 */
@@ -78,7 +78,7 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
 	/* GPR21 used for percpu base (runtime), initialized as 0 */
 	or		u0, zero, 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