From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>
Subject: Re: Remaining randconfig objtool warnings, linux-next-20200428
Date: Tue, 28 Apr 2020 17:03:53 -0500 [thread overview]
Message-ID: <20200428220353.uepo455bj76sym4k@treble> (raw)
In-Reply-To: <20200428215554.GA16027@hirez.programming.kicks-ass.net>
On Tue, Apr 28, 2020 at 11:55:54PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 28, 2020 at 03:38:55PM -0500, Josh Poimboeuf wrote:
> > This one makes no sense to me. It looks like the assembler is inserting
> > a jump as part of the alignment padding??? WTH.
> >
> > 0000000000000980 <common_spurious>:
> > 980: 48 83 04 24 80 addq $0xffffffffffffff80,(%rsp)
> > 985: e8 00 00 00 00 callq 98a <common_spurious+0xa>
> > 986: R_X86_64_PLT32 interrupt_entry-0x4
> > 98a: e8 00 00 00 00 callq 98f <common_spurious+0xf>
> > 98b: R_X86_64_PLT32 smp_spurious_interrupt-0x4
> > 98f: eb 7e jmp a0f <ret_from_intr>
> > 991: eb 6d jmp a00 <common_interrupt>
> > 993: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 99a: 00 00 00 00
> > 99e: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9a5: 00 00 00 00
> > 9a9: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9b0: 00 00 00 00
> > 9b4: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9bb: 00 00 00 00
> > 9bf: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9c6: 00 00 00 00
> > 9ca: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9d1: 00 00 00 00
> > 9d5: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9dc: 00 00 00 00
> > 9e0: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9e7: 00 00 00 00
> > 9eb: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
> > 9f2: 00 00 00 00
> > 9f6: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
> > 9fd: 00 00 00
>
> binutils.git/gas/configure/tc-i386.c:i386_generate_nops
>
> When there's too many NOPs (as here) it generates a JMP across the NOPS.
> It makes some sort of sense, at some point executing NOPs is going to be
> more expensive than a branch.. But shees..
Urgh. Even if I tell it specifically to pad with NOPs, it still does
this "trick". I have no idea how to deal with this in objtool.
--
Josh
next prev parent reply other threads:[~2020-04-28 22:04 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 14:49 Remaining randconfig objtool warnings, linux-next-20200428 Arnd Bergmann
2020-04-28 16:10 ` Josh Poimboeuf
2020-04-28 19:11 ` Kees Cook
2020-04-28 20:19 ` Arnd Bergmann
2020-04-28 20:38 ` Josh Poimboeuf
2020-04-28 21:55 ` Peter Zijlstra
2020-04-28 22:03 ` Josh Poimboeuf [this message]
2020-04-28 22:33 ` Peter Zijlstra
2020-04-28 22:48 ` Josh Poimboeuf
2020-04-28 23:08 ` Josh Poimboeuf
2020-04-29 18:55 ` Josh Poimboeuf
2020-04-29 22:46 ` Arnd Bergmann
2020-04-29 23:01 ` Josh Poimboeuf
2020-04-29 23:11 ` Josh Poimboeuf
2020-04-29 23:28 ` Josh Poimboeuf
2020-04-30 13:41 ` Arnd Bergmann
2020-04-30 14:33 ` Josh Poimboeuf
2020-04-30 19:46 ` Josh Poimboeuf
2020-04-30 20:59 ` Arnd Bergmann
2020-04-30 21:10 ` Josh Poimboeuf
2020-04-30 21:08 ` Josh Poimboeuf
2020-04-30 23:02 ` Josh Poimboeuf
2020-04-29 19:18 ` Josh Poimboeuf
2020-05-01 12:23 ` Peter Zijlstra
2020-04-30 14:05 ` Arnd Bergmann
2020-05-01 0:28 ` Josh Poimboeuf
2020-05-01 11:41 ` Arnd Bergmann
2020-05-01 17:16 ` Peter Zijlstra
2020-05-01 12:27 ` Peter Zijlstra
2020-05-01 1:07 ` Josh Poimboeuf
2020-05-01 11:18 ` Arnd Bergmann
2020-05-01 12:33 ` Peter Zijlstra
2020-05-01 13:08 ` Arnd Bergmann
2020-05-01 15:49 ` Josh Poimboeuf
2020-05-01 17:21 ` Arnd Bergmann
2020-05-01 17:26 ` Peter Zijlstra
2020-05-01 17:50 ` Josh Poimboeuf
2020-05-01 19:47 ` Arnd Bergmann
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