linux-kernel - Re: [PATCH v8 06/11] x86/CPU: Adapt assembly for PIE support

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Message-ID: <20190708190930.GA16215@avx2>
Date:   Mon, 8 Jul 2019 22:09:30 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     thgarnie@...omium.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 06/11] x86/CPU: Adapt assembly for PIE support

Thomas Garnier wrote:
> -		"pushq $1f\n\t"
> +		"movabsq $1f, %q0\n\t"
> +		"pushq %q0\n\t"
>  		"iretq\n\t"
>  		UNWIND_HINT_RESTORE
>  		"1:"

Fake PIE. True PIE looks like this:

ffffffff81022d70 <do_sync_core>:
ffffffff81022d70:       8c d0                   mov    eax,ss
ffffffff81022d72:       50                      push   rax
ffffffff81022d73:       54                      push   rsp
ffffffff81022d74:       48 83 04 24 08          add    QWORD PTR [rsp],0x8
ffffffff81022d79:       9c                      pushf
ffffffff81022d7a:       8c c8                   mov    eax,cs
ffffffff81022d7c:       50                      push   rax
ffffffff81022d7d:  ===> 48 8d 05 03 00 00 00    lea    rax,[rip+0x3]        # ffffffff81022d87 <do_sync_core+0x17>
ffffffff81022d84:       50                      push   rax
ffffffff81022d85:       48 cf                   iretq
ffffffff81022d87:       c3                      ret

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>

--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -710,7 +710,8 @@ static inline void sync_core(void)
 		"pushfq\n\t"
 		"mov %%cs, %0\n\t"
 		"pushq %q0\n\t"
-		"pushq $1f\n\t"
+		"leaq 1f(%%rip), %q0\n\t"
+		"pushq %q0\n\t"
 		"iretq\n\t"
 		UNWIND_HINT_RESTORE
 		"1:"