linux-kernel - Re: [PATCH] x86/ptrace: Remove questionable TS

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Date:	Mon, 20 Jun 2016 11:27:02 +0100
From:	Pedro Alves <pedro@...ves.net>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Oleg Nesterov <oleg@...hat.com>, Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pedro Alves <palves@...hat.com>
Subject: Re: [PATCH] x86/ptrace: Remove questionable TS_COMPAT usage in ptrace

On 06/19/2016 11:09 PM, Andy Lutomirski wrote:
> 
> The latter bit is a mess and is probably broken on current kernels for
> 64-bit gdb attached to a 32-bit process.  (Is it?  All of this stuff
> is a bit of a pain to test.)

The testcase at:

 https://sourceware.org/ml/gdb/2014-05/msg00004.html

still fails for me on Fedora 23 with git master gdb.

Nevermind the misleading URL, that's a kernel patch.

 $ gcc -g -m32 interrupt.c -o interrupt.32
 ...
 (gdb) r
 Starting program: /home/pedro/tmp/interrupt.32 
 talk to me baby
 ^C
 Program received signal SIGINT, Interrupt.
 0xf7fd9d49 in __kernel_vsyscall ()
 (gdb) p func1()
 $1 = 4
 (gdb) c
 Continuing.
 Unknown error 512
 [Inferior 1 (process 20252) exited with code 01]
 (gdb) 

That was a 64-bit gdb.

Note it doesn't fail with fedora 23's gdb, because of a 
fedora-local workaround.

Thanks,
Pedro Alves