linux-kernel - Re: [PATCH v2] um: Avoid longjmp/setjmp symbol clashes with libpthread.a

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Message-ID: <3672f56d-da81-1114-f06a-ac99d3680661@gmail.com>
Date:   Thu, 1 Jun 2017 22:49:03 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Thomas Meyer <thomas@...3r.de>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org
Cc:     Jeff Dike <jdike@...toit.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-devel@...ts.sourceforge.net>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [PATCH v2] um: Avoid longjmp/setjmp symbol clashes with
 libpthread.a



On 06/01/2017 02:25 PM, Thomas Meyer wrote:
> Am Donnerstag, den 01.06.2017, 22:58 +0200 schrieb Richard Weinberger:
>>
>> Sorry, I thought you are CC'ed.
>> Thomas please speak up. AFAIR UML fails to boot on one of your new
>> Laptops.
> 
> Hi,
> 
> yes, the first userspace process failes here:
> 
> void userspace(struct uml_pt_regs *regs)
> {
>         int err, status, op, pid = userspace_pid[0];
>         /* To prevent races if using_sysemu changes under us.*/
>         int local_using_sysemu;
>         siginfo_t si;
> 
>         /* Handle any immediate reschedules or signals */
>         interrupt_end();
> 
>         while (1) {
> 
>                 /*
>                  * This can legitimately fail if the process loads a
>                  * bogus value into a segment register.  It will
>                  * segfault and PTRACE_GETREGS will read that value
>                  * out of the process.  However, PTRACE_SETREGS will
>                  * fail.  In this case, there is nothing to do but
>                  * just kill the process.
>                  */
>                 if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
>                         fatal_sigsegv();
> 
>                 if (put_fp_registers(pid, regs->fp))
> ->                        fatal_sigsegv();
> 
> the put_fp_registers fails with errno 4 if I recall correctly.
> 
> I didn't investigate yet further, why the the xstate ptrace call fails.

Which of the branches is put_fp_registers() taking? The
restore_fpx_registers() or restore_fp_registers()? 4 would be EINTR...
What kernel version is used on your host running the UML binary?

Thanks
-- 
Florian