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Date:      Fri, 4 Jan 2019 19:29:51 -0800
From:      Mark Millard <marklmi@yahoo.com>
To:        Kyle Evans <kevans@FreeBSD.org>, freebsd-emulation@freebsd.org, ports-list freebsd <freebsd-ports@freebsd.org>
Cc:        Sean Bruno <sbruno@freebsd.org>
Subject:   qemu-x86_64-static has target_freebsd_flock being too large (__packed use issue)
Message-ID:  <1139EAD0-FED3-428C-AA0E-00ABB8BD111D@yahoo.com>
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[qemu-aarch64-static has the same problem but qemu-armv7-sstatic does =
not. The context here
is FreeBSD head -r341836 based and ports head -r488859 based.]

Note: I assume that "struct target_freebsd_flock" is meant to match the =
memory layout
of the target's native "struct flock". Otherwise the reported =
differences
below could be irrelevant.

For amd64 and aarch64 the following code:

        printf("sizeof(struct flock) =3D %lu\n", (unsigned long) =
sizeof(struct flock));
        printf("l_start %lu\n", (unsigned long) offsetof(struct flock, =
l_start));
        printf("l_len %lu\n", (unsigned long) offsetof(struct flock, =
l_len));
        printf("l_pid %lu\n", (unsigned long) offsetof(struct flock, =
l_pid));
        printf("l_type %lu\n", (unsigned long) offsetof(struct flock, =
l_type));
        printf("l_whence %lu\n", (unsigned long) offsetof(struct flock, =
l_whence));
        printf("l_sysid %lu\n", (unsigned long) offsetof(struct flock, =
l_sysid));
=20

produces:

sizeof(struct flock) =3D 32
l_start 0
l_len 8
l_pid 16
l_type 20
l_whence 22
l_sysid 24


However gdb reports for qemu-x86_64-static and qemu-aarch64-static
and qemu-arm-static:

(gdb) p/d sizeof(struct target_freebsd_flock)
$10 =3D 28
(gdb) p/d &((struct target_freebsd_flock *)0)->l_start =20
$11 =3D 0
(gdb) p/d &((struct target_freebsd_flock *)0)->l_len =20
$12 =3D 8
(gdb) p/d &((struct target_freebsd_flock *)0)->l_pid
$13 =3D 16
(gdb) p/d &((struct target_freebsd_flock *)0)->l_type
$14 =3D 20
(gdb) p/d &((struct target_freebsd_flock *)0)->l_whence
$15 =3D 22
(gdb) p/d &((struct target_freebsd_flock *)0)->l_sysid=20
$16 =3D 24

So only the overall size is different for this information. But:

struct target_freebsd_flock {
    int64_t l_start;
    int64_t l_len;
    int32_t l_pid;
    int16_t l_type;
    int16_t l_whence;
    int32_t l_sysid;
} QEMU_PACKED;

with a potential packed vs. /usr/include/sys/fcntl.h :

struct flock {
        off_t   l_start;        /* starting offset */
        off_t   l_len;          /* len =3D 0 means until end of file */
        pid_t   l_pid;          /* lock owner */
        short   l_type;         /* lock type: read/write, etc. */
        short   l_whence;       /* type of l_start */
        int     l_sysid;        /* remote system id or zero for local */
};

with no potential __packed.


=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)

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