Michael Eskin wrote...
> but in all cases when running the tool even on very simple
> console mode "Hello World" applications, we're immediately
> getting a SIGILL crash on what appears to be the _start function
> in ucLibc before hitting any of our code.
...
> Here's the sort of thing we're running into, would appreciate
> any suggestions for what might be going on, we're completely
> stuck at this point...
>
>
> # valgrind -v ./diftDec dift_422cmode2_no_hdr.data output.dat -hdr -f 422
> Illegal instruction
>
I'm seeing the same symptom on a cortex a9 (see 1 below) which doesn't have the
SIMD (neon) nor VFP extensions. From the arm reference manual: "Advanced SIMD
and VFP are two optional extensions to ARMv7". My board doesnt have those
options, just the embedded FPU.
A debug session (see 2 below) shows that the problem for my board occurs in
coregrind/m_dispatch/dispatch-arm-linux.S:
#if defined(VGP_arm_linux)
.fpu vfp
....
VG_(run_innerloop):
push {r0, r1, r4, r5, r6, r7, r8, r9, fp, lr}
/* set FPSCR to vex-required default value */
mov r4, #0
fmxr fpscr, r4 <== illegal instruction here
The failure makes sense - the fpscr register is a SIMD/vfp extension register
and fmxr (now replaced by 'vmsr') is invalid without those extensions.
I experimented patching out the unimplemented opcodes, but as implied by the
comment 'vex-required default value' , there was an invariant failure (see 3
below) which I haven't tracked down yet.
Any clues/patches around the fpscr register usage for the armv7 be appreciated.
Detailed Output:
====================
1) Failure with the Cortex A9:
# valgrind /usr/bin/find
==753== Memcheck, a memory error detector
==753== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==753== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==753== Command: /usr/bin/find
==753==
==753==
==753== Process terminating with default action of signal 4 (SIGILL)
==753== Illegal opcode at address 0x38143358
==753== at 0x4000790: ??? (in /lib/ld-2.11.1.so)
==753==
==753== HEAP SUMMARY:
==753== in use at exit: 0 bytes in 0 blocks
==753== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==753==
==753== All heap blocks were freed -- no leaks are possible
==753==
==753== For counts of detected and suppressed errors, rerun with: -v
==753== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Illegal instruction
Comments:The application address (never actually emitted/executes) 0x4000790 is
at _start in ld.so
objdump -d ld-2.11.1.so
....
Disassembly of section .text:
00000790 <_start>:
790: f8df a068 ldr.w sl, [pc, #104] ; 7fc
<_dl_start_user+0x5e>
794: f8df 4068 ldr.w r4, [pc, #104] ; 800
<_dl_start_user+0x62>
798: 4668 mov r0, sp
79a: f000 f9fd bl b98 <_dl_start>
====================
2) Isolating failure in gdb session
term1> valgrind --wait-for-gdb=yes /usr/bin/find
term2>
handle SIGILL SIGSEGV nostop noprint >> .gdbinit
gdb /usr/lib/valgrind/memcheck-ppc32-linux 231
...
(gdb) c
Continuing.
Program received signal SIGILL, Illegal instruction.
vgPlain_run_innerloop () at m_dispatch/dispatch-arm-linux.S:61
61 m_dispatch/dispatch-arm-linux.S: No such file or directory.
in m_dispatch/dispatch-arm-linux.S
Comments: the location is the unimplemented opcode on the unimplemented
register.
====================
3) Failure with (probably naive) patched out vfp instructions at
dispatch-armn-linux.S:61...
# valgrind /usr/bin/find
==719== Memcheck, a memory error detector
==719== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==719== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==719== Command: /usr/bin/find
==719==
valgrind: m_scheduler/scheduler.c:1232 (vgPlain_scheduler): the 'impossible'
happened.
valgrind: VG_(scheduler), phase 3: run_innerloop detected host state invariant
failure
==719== at 0x380574B4: report_and_quit (m_libcassert.c:209)
==719== by 0x38057763: vgPlain_assert_fail (m_libcassert.c:283)
==719== by 0x380BC773: vgPlain_scheduler (scheduler.c:1230)
==719== by 0x380D9A47: thread_wrapper (syswrap-linux.c:94)
==719== by 0x380D9BCB: run_a_thread_NORETURN (syswrap-linux.c:127)
==719== by 0xFFFFFFFF: ???
sched status:
running_tid=1
Thread 1: status = VgTs_Runnable
==719== at 0x4000B98: _dl_start_final (rtld.c:363)
==719== by 0x400079D: ??? (in /lib/ld-2.11.1.so)
...
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