Re: [PATCH] Seg fault whilst stepping when watch set [ping!] [inbreakpoint.c]

[David Lecomber <david at streamline-computing dot com>]

Hi Eli,

Ping * 3!  

d.
On Wed, 2004-11-03 at 12:08, David Lecomber wrote:
> Hi Eli,
> 
> Breakpoint 1, 0x08089e8a in main ()
> (gdb) step
> Single stepping until exit from function main,
> which has no line number information.
> sample () at f90demo.f90:72
> 72      CALL MPI_INIT(ierr)
> Current language:  auto; currently fortran
> (gdb) watch i
> Hardware watchpoint 2: i
> (gdb) n
> Error in re-setting breakpoint 2:
> No symbol "i" in current context.
>  
> {seg fault...} and in the other GDB:
> Program received signal SIGSEGV, Segmentation fault.
> evaluate_subexp (expect_type=0x0, exp=0x0, pos=0xbfffef34,
> noside=EVAL_NORMAL) at eval.c:71
> 71        return (*exp->language_defn->la_exp_desc->evaluate_exp)
> 
> 
> #0  evaluate_subexp (expect_type=0x0, exp=0x0, pos=0xbfffef34,
> noside=EVAL_NORMAL) at eval.c:71
> #1  0x080d3fa9 in evaluate_expression (exp=0x0) at eval.c:161
> #2  0x080c4341 in insert_bp_location (bpt=0x82d8458,
> tmp_error_stream=0x82de608, disabled_breaks=0xbfffefd0,
> process_warning=0xbfffefd4,
>     hw_breakpoint_error=0xbfffefd8) at breakpoint.c:949
> #3  0x080c45a7 in insert_breakpoints () at breakpoint.c:1149
> #4  0x080f43cd in keep_going (ecs=0xbffff0d0) at infrun.c:2716
> #5  0x080f2f47 in handle_inferior_event (ecs=0xbffff0d0) at
> infrun.c:2543
> #6  0x080f270b in wait_for_inferior () at infrun.c:991
> #7  0x080f253d in proceed (addr=1, siggnal=TARGET_SIGNAL_DEFAULT,
> step=1) at infrun.c:814
> #8  0x080efe9b in step_1 (skip_subroutines=1, single_inst=0,
> count_string=0x0) at infcmd.c:688
> 
> (gdb) p exp
> $1 = (struct expression *) 0x0
> 
> Looking at frame 2:
> 
> #2  0x080c4341 in insert_bp_location (bpt=0x82d8458,
> tmp_error_stream=0x82de608, disabled_breaks=0xbfffefd0,
> process_warning=0xbfffefd4,
>     hw_breakpoint_error=0xbfffefd8) at breakpoint.c:949
> 949               v = evaluate_expression (bpt->owner->exp);
> 
> 
> (gdb) p *bpt
> $5 = {next = 0x82de5d8, loc_type = bp_loc_hardware_watchpoint, owner =
> 0x835f3f0, inserted = 0 '\0', duplicate = 0 '\0', address = 0, section =
> 0x0,
>   shadow_contents = '\0' <repeats 15 times>, requested_address = 0}
> (gdb) p *(bpt->owner)
> $6 = {next = 0x83ac680, type = bp_hardware_watchpoint, enable_state =
> bp_enabled, disposition = disp_donttouch, number = 2, loc = 0x82d8458,
> line_number = 0,
>   source_file = 0x0, silent = 0 '\0', ignore_count = 0, commands = 0x0,
> frame_id = {stack_addr = 0, code_addr = 0, special_addr = 0,
> stack_addr_p = 0,
>     code_addr_p = 0, special_addr_p = 0}, cond = 0x0, addr_string = 0x0,
> language = language_fortran, input_radix = 10, cond_string = 0x0,
> exp_string = 0x835d408 "i",
>   exp = 0x0, exp_valid_block = 0x841723c, val = 0x835f8d8, val_chain =
> 0x0, related_breakpoint = 0x83ac680, watchpoint_frame = {stack_addr =
> 3221223780,
>     code_addr = 134526326, special_addr = 0, stack_addr_p = 1,
> code_addr_p = 1, special_addr_p = 0}, thread = -1, hit_count = 0,
> dll_pathname = 0x0,
>   triggered_dll_pathname = 0x0, forked_inferior_pid = 0, exec_pathname =
> 0x0, ops = 0x0, from_tty = 0, flag = 0, pending = 0}
> 
> So bpt->owner->exp is clearly null, which makes it a bad idea to
> evaluate it ;-)
> 
> > If the binary is short, then you could alternatively mail it to me as
> > a binary attachment together with the source and instructions how to
> > reproduce the crash.
> 
> Curiously on Fedora 2 I get a seg fault, and
> 
> Error in re-setting breakpoint 2:
> No symbol "i" in current context.
> 
> But on Redhat 9, I get no segfault but do see the above error repeated 3
> times..  
> 
> With my patch, it works fine, for me ;-)
> 
> d.
>