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

[John Baldwin]

On Tuesday, October 25, 2016 11:40:38 AM Mark Millard wrote:
> [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

I have a patchset I have tested some in a git branch that I believe fixes handling of
unknown system calls.  Please try this:

https://github.com/freebsd/freebsd/compare/master...bsdjhb:truss_unknown

(Add .diff to get a diff you can apply with patch)

-- 
John Baldwin