linux-kernel - [PATCH V2 09/41] x86/entry: Expose the address of .Lgs

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Date:   Sun, 26 Sep 2021 23:08:06 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH V2 09/41] x86/entry: Expose the address of .Lgs_change to entry64.c

From: Lai Jiangshan <laijs@...ux.alibaba.com>

The address of .Lgs_change will be used in traps.c in later patch when
some entry code is implemented in entry64.c.  So the address of .Lgs_change
is exposed to traps.c for preparation.

The label .Lgs_change is still needed in ASM code for extable due to it
can not use asm_load_gs_index_gs_change.  Otherwise:

	warning: objtool: __ex_table+0x0: don't know how to handle
	non-section reloc symbol asm_load_gs_index_gs_change

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/entry/entry64.c  | 2 ++
 arch/x86/entry/entry_64.S | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry64.c b/arch/x86/entry/entry64.c
index 3a6d70367940..7272266a3726 100644
--- a/arch/x86/entry/entry64.c
+++ b/arch/x86/entry/entry64.c
@@ -9,3 +9,5 @@
  * is PTI user CR3 or both.
  */
 #include <asm/traps.h>
+
+extern unsigned char asm_load_gs_index_gs_change[];
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 95d85b16710b..291732f571a7 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -729,6 +729,7 @@ _ASM_NOKPROBE(common_interrupt_return)
 SYM_FUNC_START(asm_load_gs_index)
 	FRAME_BEGIN
 	swapgs
+SYM_INNER_LABEL(asm_load_gs_index_gs_change, SYM_L_GLOBAL)
 .Lgs_change:
 	movl	%edi, %gs
 2:	ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
@@ -1006,7 +1007,7 @@ SYM_CODE_START_LOCAL(error_entry)
 	movl	%ecx, %eax			/* zero extend */
 	cmpq	%rax, RIP+8(%rsp)
 	je	.Lbstep_iret
-	cmpq	$.Lgs_change, RIP+8(%rsp)
+	cmpq	$asm_load_gs_index_gs_change, RIP+8(%rsp)
 	jne	.Lerror_entry_done_lfence
 
 	/*
-- 
2.19.1.6.gb485710b