Date: Wed, 6 Dec 2023 20:31:13 -0800 From: Mark Millard <marklmi@yahoo.com> To: Warner Losh <imp@bsdimp.com>, Current FreeBSD <freebsd-current@freebsd.org>, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Cc: dan@langille.org Subject: aarch64 and armv6 vs. armv7 support: armv6 is not supported, despite what "man arch" reports Message-ID: <3C33BBA5-A84D-4F46-B38E-B67F9FE0196D@yahoo.com> References: <3C33BBA5-A84D-4F46-B38E-B67F9FE0196D.ref@yahoo.com>
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man arch reports:
QUOTE
Some machines support more than one FreeBSD ABI. Typically these =
are
64-bit machines, where the =E2=80=9Cnative=E2=80=9D LP64 execution =
environment is
accompanied by the =E2=80=9Clegacy=E2=80=9D ILP32 environment, =
which was the historical
32-bit predecessor for 64-bit evolution. Examples are:
LP64 ILP32 counterpart
amd64 i386
powerpc64 powerpc
aarch64 armv6/armv7
aarch64 will support execution of armv6 or armv7 binaries if the =
CPU
implements AArch32 execution state, however older armv4 and armv5
binaries aren't supported.
END QUOTE
(I take "armv6 or armv7 binaries" as what was built targeting a FreeBSD
architecture triple for one of those. FreeBSD keeps them distinct.)
However, the armv6 part of that is wrong: The infrastructure supports
only one 32-bit alternative for a given kernel, not a family of them at
once . . .
sys/kern/kern_mib.c :
static const char *
proc_machine_arch(struct proc *p)
{
if (p->p_sysent->sv_machine_arch !=3D NULL)
return (p->p_sysent->sv_machine_arch(p));
#ifdef COMPAT_FREEBSD32
if (SV_PROC_FLAG(p, SV_ILP32))
return (MACHINE_ARCH32);
#endif
return (MACHINE_ARCH);
}
. . .
static int
sysctl_kern_supported_archs(SYSCTL_HANDLER_ARGS)
{
const char *supported_archs;
supported_archs =3D
#ifdef COMPAT_FREEBSD32
compat_freebsd_32bit ? MACHINE_ARCH " " MACHINE_ARCH32 :
#endif
MACHINE_ARCH;
return (SYSCTL_OUT(req, supported_archs, strlen(supported_archs) =
+ 1));
}
sys/arm64/include/param.h :
#define MACHINE_ARCHES MACHINE_ARCH " " MACHINE_ARCH32
. . .
#define MACHINE_ARCH32 "armv7"
(There is no "armv6" alternative present.)
But with something like:
#define MACHINE_ARCH32 "armv7 armv6"
MACHINE_ARCH32 is not interpreted as a list of alternatives, each
supported. There is code that would have to be reworked to allow
a list of alternatives to work.
One can build a custom kernel with:
#define MACHINE_ARCH32 "armv6"
and then, having booted that kernel, then run armv6 on aarch64
--but, then, not armv7.
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D256132 is
about this and has my messy notes as I explored and discovered
that multiple 32-bit alternatives did not work. I see that I
forgot various quote (") symbols.
This note was prompted by:
=
https://lists.freebsd.org/archives/freebsd-hackers/2023-December/002728.ht=
ml
that mentions "the list of valid MACHINE_ARCH" that reminded me
of this old issue.
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
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