linux-kernel - Re: Clang patch stacks for LTS kernels (v4.4 and v4.9) and status update

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Date:   Tue, 22 May 2018 14:17:45 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Manoj Gupta <manojgupta@...omium.org>,
        AlistairStrachan <astrachan@...gle.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: Re: Clang patch stacks for LTS kernels (v4.4 and v4.9) and status update

For the sake of completeness...

[ CLANG VERSION ]

# dpkg -l | grep clang-7
ii  clang-7
1:7~svn332830-1~exp1+0~20180521091322.1776~1.gbp198359 amd64        C,
C++ and Objective-C compiler

[ OBJDUMP native_save_fl() ]

$ objdump -d -S --start-address=0x$(grep native_save_fl System.map |
sed -e "s/ \+.*//") vmlinux | less

vmlinux:     file format elf64-x86-64


Disassembly of section .text:

ffffffff810633a0 <native_save_fl>:
/*
 * Interrupt control:
 */

static inline __nostackprotector unsigned long native_save_fl(void)
{
ffffffff810633a0:       55                      push   %rbp
ffffffff810633a1:       48 89 e5                mov    %rsp,%rbp
ffffffff810633a4:       50                      push   %rax
        /*
         * "=rm" is safe here, because "pop" adjusts the stack before
         * it evaluates its effective address -- this is part of the
         * documented behavior of the "pop" instruction.
         */
        asm volatile("# __raw_save_flags\n\t"
ffffffff810633a5:       9c                      pushfq
ffffffff810633a6:       8f 45 f8                popq   -0x8(%rbp)
                     "pushf ; pop %0"
                     : "=rm" (flags)
                     : /* no input */
                     : "memory");

        return flags;
ffffffff810633a9:       48 8b 45 f8             mov    -0x8(%rbp),%rax
ffffffff810633ad:       48 83 c4 08             add    $0x8,%rsp
ffffffff810633b1:       5d                      pop    %rbp
ffffffff810633b2:       c3                      retq
ffffffff810633b3:       0f 1f 00                nopl   (%rax)
ffffffff810633b6:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
ffffffff810633bd:       00 00 00

ffffffff810633c0 <native_restore_fl>:
}

static inline void native_restore_fl(unsigned long flags)
{
...

- Sedat -