stable/11 -r307797 on BPi-M3 (cortex-a7): truss gets segmentation fault for handling unknown system call

From: Mark Millard <markmi_at_dsl-only.net>
Date: Tue, 25 Oct 2016 11:40:38 -0700
[The following has been reported in: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=213778 .]

In trying to build lang/gcc6 xgcc's cc1 got some SIGSYS examples. In trying to track things down I ran into truss getting a SIGSEGV when it tries to handle the situation. . .

In truss's enter_syscall there is (from a live gdb on truss, after the segmentation fault):

380		t->cs.name = sysdecode_syscallname(t->proc->abi->abi, t->cs.number);
381		if (t->cs.name == NULL)
(gdb) 
382			fprintf(info->outfile, "-- UNKNOWN %s SYSCALL %d --\n",
383			    t->proc->abi->type, t->cs.number);
384	
385		sc = get_syscall(t->cs.name, narg);
386		t->cs.nargs = sc->nargs;
387		assert(sc->nargs <= nitems(t->cs.s_args));
388	
389		t->cs.sc = sc;

(gdb) print *t
$2 = {entries = {le_next = 0x0, le_prev = 0x20617070}, proc = 0x20617060, tid = 100150, in_syscall = 1, cs = {sc = 0x0, name = 0x0, number = 580828064, args = 0x2061b0c0, nargs = 0, 
    s_args = 0x2061b0ec}, before = {tv_sec = 1477418265, tv_nsec = 492342263}, after = {tv_sec = 1477418265, tv_nsec = 492496630}}

(gdb) print sc
$3 = (struct syscall *) 0x0

So line 386 listed above gets a segmentation fault for sc->nargs when t->cs.name is a NULL pointer: sc ends up NULL.

Looking at the two things that the fprintf on lines 382 and 383 would report:

(gdb) print t->proc->abi->type
$4 = 0x10166 "FreeBSD ELF32"

(gdb) print t->cs.number
$5 = 580828064

(gdb) print narg
$6 = 0

(that last is for context for the get_syscall arguments).

FYI: 580828064 = 0x229EBBA0


Context:

root_at_bananapi-m3:/usr/ports # uname -apKU
FreeBSD bananapi-m3 11.0-STABLE FreeBSD 11.0-STABLE #0 r307797M: Mon Oct 24 00:41:16 PDT 2016     markmi_at_FreeBSDx64:/usr/local/src/crochet/work/obj/arm.armv6/usr/src/sys/ALLWINNER  arm armv6 1100505 1100505



===
Mark Millard
markmi at dsl-only.net
Received on Tue Oct 25 2016 - 16:47:21 UTC

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