Date: Sat, 30 Jan 2016 12:29:13 +0100 From: Roman Divacky <rdivacky@vlakno.cz> To: Mark Millard <markmi@dsl-only.net> Cc: FreeBSD PowerPC ML <freebsd-ppc@freebsd.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org> Subject: Re: clang 3.8.0 based powerpc (32 bit) buildworld runs on a PowerMac! [problems found] Message-ID: <20160130112913.GA7950@vlakno.cz> In-Reply-To: <55814789-0489-48B5-867C-F678AE4EA5FF@dsl-only.net> References: <DEF41968-FFC4-417D-A31A-E392CB888C35@dsl-only.net> <55814789-0489-48B5-867C-F678AE4EA5FF@dsl-only.net>
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Can you file a bug in llvm bugzilla?
On Sat, Jan 30, 2016 at 03:00:26AM -0800, Mark Millard wrote:
> I got around to trying some more use of the 3.8.0 clang based world on powerpc (32 bit) (now -r294962 based) and ran into:
>
> A) Segmentation faults during signal handlers in syslogd, nfsd, mountd, and (for SIGNFO) make.
>
> B) ls sometimes segmentation faulting
>
> C) make -j 6 buildworld segmentation faulting in make eventually but make buildworld works.
>
> I have reduced (A) to a simple program that demonstrates the behavior:
>
> > # more sig_snprintf_use_test.c
> > #include <stdio.h>
> > #include <signal.h>
> >
> > volatile sig_atomic_t sat = 0;
> >
> > void
> > handler(int sig)
> > {
> > char uidbuf[32];
> > (void) snprintf(uidbuf, sizeof uidbuf, "%d", 10);
> > sat = uidbuf[0];
> > }
> >
> > int
> > main(void)
> > {
> > if (signal(SIGINT, handler) != SIG_ERR) raise(SIGINT);
> > return sat;
> > }
>
> > # ./a.out
> > Segmentation fault (core dumped)
> > # /usr/local/bin/gdb a.out /var/crash/a.out.1510.core
> > GNU gdb (GDB) 7.10 [GDB v7.10 for FreeBSD]
> . . .
> > warning: Unexpected size of section `.reg2/100167' in core file.
> > #0 0x419a89c8 in memcpy (dst0=0xffffd734, src0=<optimized out>, length=<optimized out>) at /usr/src/lib/libc/string/bcopy.c:124
> > 124 TLOOP1(*--dst = *--src);
> > (gdb) bt
> > #0 0x419a89c8 in memcpy (dst0=0xffffd734, src0=<optimized out>, length=<optimized out>) at /usr/src/lib/libc/string/bcopy.c:124
> > #1 0x419a3984 in __sfvwrite (fp=<optimized out>, uio=<optimized out>) at /usr/src/lib/libc/stdio/fvwrite.c:128
> > #2 0x41934468 in __sprint (fp=<optimized out>, uio=<optimized out>, locale=<optimized out>) at /usr/src/lib/libc/stdio/vfprintf.c:164
> > #3 io_flush (iop=<optimized out>, locale=<optimized out>) at /usr/src/lib/libc/stdio/printfcommon.h:155
> > #4 __vfprintf (fp=<optimized out>, locale=<optimized out>, fmt0=<optimized out>, ap=<optimized out>) at /usr/src/lib/libc/stdio/vfprintf.c:1020
> > #5 0x4199c644 in snprintf (str=0xffffd734 "", n=<optimized out>, fmt=0x1800850 "%d") at /usr/src/lib/libc/stdio/snprintf.c:72
> > #6 0x01800708 in handler ()
> > Backtrace stopped: Cannot access memory at address 0xffffd760
>
> (The "Unexpected size . . ." is a known problem in powerpc land at this point, not tied to clang 3.8.0 .)
>
> The syslogd, nfsd, mountd, and SIGINFO-related make backtraces are similar. I got the program above from simplifying the mountd failure context.
>
> A direct call, handler(0), does not get the segmentation fault.
>
> I'll note that in C the handler calling snprintf or other such is a no-no for the general case: only abort(), _Exit(), or signal() as of C99 as I understand. But the restriction is not true of use of raise so the small program is still valid C99 code. Of course it appears FreeBSD allows more than C99 does in this area.
>
> I've not yet investigated what the original signals are in syslogd, nfsd, or mountd. They may well indicate another problem.
>
>
> I've not gotten as far classifying (B) or (C) as well.
>
> (B) is a xo_emit context each time so far (so C elipsis use again, like (A)) but no signal handler seems to be active. It stops in xo_format_string_direct. My attempts at simpler code have not produced the problem so far.
>
> (C) is such that GDB 7.10 reports "previous frame to this frame (corrupt stack?)" or otherwise gives up. It shows Var_Value called by Make_Update before reporting that. gdb 6.1.1 shows more after that: JobFinish, JobReapChild, Job_CatchChildern, Job_CatchOutput, Make_Run, main). SIGCHLD or other such use may well be involved here.
>
>
> ===
> Mark Millard
> markmi at dsl-only.net
>
> On 2016-Jan-19, at 2:35 AM, Mark Millard <markmi@dsl-only.net> wrote:
>
> I now have an SSD that contains:
>
> 0) installkernel material from a gcc 4.2.1 based buildkernel
>
> 1) installworld material from a clang 3.8.0 based buildworld
> (clang 3.8.0, libc++, etc.)
>
> It boots and seems to be operating fine after booting --in both a G5 and a G4 PowerMac.
>
> Apparently the clang code generation has been updated to not require an explicit -mlongcall. I had to remove those since clang rejects them on command lines. It linked without complaint (and later seems to be running fine). (I've seen llvm review notes mentioning the "medium model" or some phrase like that for powerpc.)
>
> (I've not been able to buildkernel yet for powerpc (non-64) from my amd64 environment: rejected command lines for other issues. Thus the current limitation to buildworld.)
>
>
>
> To get to (1) I did the following sort of sequence:
> (The first few steps deal with other issues in order to have sufficient context.)
>
>
> A) Started by installing the latest powerpc (non-64) snapshot.
> ( http://ftp1.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/11.0/FreeBSD-11.0-CURRENT-powerpc-20160113-r293801-disc1.iso )
>
> (I had to use a PowerMac with video hardware that vt would handle.)
> (Basic display, no X-windows involvement here.)
>
>
> B) Rebuild, including using my usual kernel configuration that has
> both vt and sc. I did this based on projects/clang380-import
> -r294201 /usr/src but still using gcc 4.2.1 (native on the
> PowerMac). The configuration turns off kernel debugging extras too.
>
>
> C) installkernel, installworld, etc., set to use sc instead of vt, and rebooted.
>
> (As of this I could use the SSD in more PowerMacs by using sc instead of vt via a /boot/loader.conf assignment.)
>
>
> D) dump/restore the file systems to another SSD (after partitioning it).
> Adjust the host name and the like on the copy.
>
> (This copy later ends up having new installworld materials overlaid.)
>
>
> E) In a projects/clang380-import -r294201 amd64 environment, buildworld for
> TARGET_ARCH=powerpc . WITH_LIBCPLUSPLUS= and clang related material built,
> gcc 4.2.1 related material not built. WITH_BOOT= as well. I choose
> WITHOUT_DEBUG= and WITHOUT_DEBUG_FILES= . (I've not tried enabling them yet.)
> binutils is not from ports.
>
>
> F) Use DESTDIR= with installworld to an initially empty directory tree. tar the tree.
>
>
> G) Transfer the tar file to the PowerMac. Mount the to-be-updated SSD to
> /mnt and /mnt/var. After chflags -R noschg on /mnt and /mnt/var use
> tar xpf to replace things from the buildworld on /mnt and /mnt/var.
>
> (This does leave older gcc 4.2.1 related materials in place.)
>
> H) Dismounts, shutdown, and then boot from the updated SSD.
>
>
>
> Note: I've never manage to get powerpc64-xtoolchain-gcc/powerpc64-gcc to produce working 32-bit code. So I've never gotten this far via that path.
>
>
> ===
> Mark Millard
> markmi at dsl-only.net
>
>
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