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Date:      Mon, 11 Feb 2008 18:16:21 +0200
From:      Andriy Gapon <avg@icyb.net.ua>
To:        freebsd-emulation@freebsd.org
Subject:   bug in recent linux mmap changes ?
Message-ID:  <47B074D5.1020602@icyb.net.ua>
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After upgrading two machines, one to 6.3 and the other to 7.0-RC1, I can
not run linux heroes3 anymore (statically linked, threaded application
originally written for kernel 2.2.X). On 6.3 the process "hangs", on
7.0-RC1 one of the threads/processes crashes with SIGSEGV.
Everything was OK as recently as 6.2.

I can provide more diagnostics later, if needed, but in both cases I see
that the last system call in a troublesome thread/process is linux_mmap().
I did a brief search through recent linux_mmap changes and I think that
there is a bug in the following commit (I am writing this hastiliy, so I
haven't yet tested a possible fix):
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/i386/linux/linux_machdep.c.diff?r1=1.48.2.4;r2=1.48.2.5;f=h

Namely, old code:
====================================================
/* This gives us TOS */
bsd_args.addr = linux_args->addr + linux_args->len;

if (bsd_args.addr > p->p_vmspace->vm_maxsaddr) {
[block folded]
}

/* This gives us our maximum stack size */
if (linux_args->len > STACK_SIZE - GUARD_SIZE)
        bsd_args.len = linux_args->len;
else
        bsd_args.len  = STACK_SIZE - GUARD_SIZE;

/*
[comment folded]
 */
bsd_args.addr -= bsd_args.len;
====================================================

New code:
====================================================
if ((caddr_t)PTRIN(linux_args->addr) + linux_args->len >
    p->p_vmspace->vm_maxsaddr) {
[block folded]
}

/* This gives us our maximum stack size */
if (linux_args->len > STACK_SIZE - GUARD_SIZE)
        bsd_args.len = linux_args->len;
else
        bsd_args.len  = STACK_SIZE - GUARD_SIZE;

/*
[comment foled]
 */
bsd_args.addr = (caddr_t)PTRIN(linux_args->addr) -
    bsd_args.len;
====================================================

Please now note that the new code doesn't have initial bsd_args.addr
assignment line. So, in summary, old code does the following:
bsd_args.addr = linux_args->addr + linux_args->len;
...
bsd_args.addr -= bsd_args.len;

While new code does:
bsd_args.addr = (caddr_t)PTRIN(linux_args->addr) - bsd_args.len;


-- 
Andriy Gapon

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