Bug#583291: Acknowledgement (menhir: segmentation fault)

[Török Edwin <edwintorok@gmail.com>]

clone 583291 -1
reassign -1 ocaml
retitle -1 ocamlopt x86_64: Stack_overflow not always generated properly
thanks

I built a bytecode version of menhir, and used OCAMLRUNPARAM=b, and got
this stacktrace (the bytecode doesn't segfault):

Fatal error: exception Stack_overflow
Raised by primitive operation at file "convert.ml", line 70, characters
27-34
Called from file "engine.ml", line 42, characters 16-32
Called from file "engine.ml", line 101, characters 4-154
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
Called from file "referenceInterpreter.ml", line 73, characters 3-30
...
Called from file "referenceInterpreter.ml", line 73, characters 3-30

Here is a gdb backtrace of the segfault though (on the core file):
#0  0x00000000004b933b in caml_equal ()
#1  0x00000000004c49bc in ?? ()
#2  0x00007f42a1a59d20 in ?? ()
#3  0x0000000000000003 in ?? ()
#4  0x0000000000000001 in ?? ()
#5  0x00007f42a1a59d60 in ?? ()
#6  0x00007f42a1a59e88 in ?? ()
#7  0x0000000000000001 in ?? ()
#8  0x00007f42a1a59d60 in ?? ()
#9  0x000000000043bad9 in ?? ()
#10 0x00007ffff54890b0 in ?? ()
#11 0x000000000043b94e in ?? ()
#12 0x00007f42a1a59ec8 in ?? ()
#13 0x00007f42a1a59cc0 in ?? ()
#14 0x00007f42a1a59ea8 in ?? ()
#15 0x00007f42a1a5a898 in ?? ()

Problem is an OCaml stack overflow exception could be caught by the app
(menhir), but a segfault not...
AFAICT in native mode OCaml catches the sigsegv, figures out it is a
stack overflow and raises the appropriate exception

So it must be something wrong in OCaml's segfault -> stack_overflow
exception conversion code on x86_64.

I tried on x86-32 (same machine, in a chroot), and the stack overflow
was always caught, no segfaults.

I'm adding some printfs to the asmrun code in the sigsegv handler, and
here it is:
in asmrun/signals_asm.c:
 printf("segv at %p %p, %d %p - %p\n%p, %p - %p: %d", fault_addr,
	((uintnat) fault_addr & (sizeof(intnat) - 1)),
	getrlimit(RLIMIT_STACK, &limit),
	system_stack_top,
	system_stack_top - limit.rlim_cur - 0x2000,
	CONTEXT_PC,
	caml_code_area_start,
	caml_code_area_end,
	Is_in_code_area(CONTEXT_PC)
	);

Output:
segv at 0x7fff38e30ff8 (nil), 0 0x7fff3962ff40 - 0x7fff3962df40
0x4b84a5, 0x41fee0 - 0x4aedd9: 0Segmentation fault

segv at 0x7fff417dfff0 (nil), 0 0x7fff41fdd1b0 - 0x7fff41fdb1b0
0x48b004, 0x41fee0 - 0x4aedd9: 1Fatal error: exception Stack_overflow

So Is_in_code_area is wrong, see above the crash is in caml_equal, yet
caml_code_area_end is below that address, and Is_in_code_area returns
false too.

Best regards,
--Edwin