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

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Date:   Thu, 01 Jun 2017 23:25:22 +0200
From:   Thomas Meyer <thomas@...3r.de>
To:     Richard Weinberger <richard@....at>,
        Florian Fainelli <f.fainelli@...il.com>,
        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

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.

kind regards
thomas


> Thanks,
> //richard