Re: [PATCH] testsuite/gdb.dwarf2: Fix for dw2-dos-drive failure on ARM

[Omair Javaid <omair.javaid@linaro.org>]

On 19 September 2013 20:53, Pedro Alves <palves@redhat.com> wrote:
> Please don't top post.
>
> On 09/19/2013 04:23 PM, Omair Javaid wrote:
>> Thanks everyone for the feedback.
>>
>> I am getting following problem with 1byte text section in the dw2-dos-drive.exp
>>
>> (gdb) PASS: gdb.dwarf2/dw2-dos-drive.exp: set breakpoint pending off
>> break 'z:file.c':func
>> Cannot access memory at address 0x0
>>
>> When I change this to 4bytes the problem gets fixed. That is why I
>> thought this could be an unaligned illegal memory access but I accept
>> that the above comments verify that its not a alignment issue.
>>
>> Can anyone help me figure out what could be the cause of this problem?
>
> Breakpoint instructions on ARM are 4-byte wide.  It sounds like
> GDB is trying to read the memory at the breakpoint's address, and
> that fails (that error message comes from GDB, not the program).
> AFAICS, the test doesn't execute the compiled object's code, so
> GDB will try to read memory from the binary's sections.  As the
> section is only 1 byte long, and probably no other section is allocated
> contiguously, that'll fail...  To confirm, debug GDB under GDB,
> and put a break on throw_it or some such.  Then work up the stack
> to see where that is thrown, and why.
>
> --
> Pedro Alves
>

I have verified the error is being thrown by gdb while its unable to
read the 4byte breakpoint address.
Heres the call stack:
Thread [1] (Suspended: Breakpoint hit.)
38 throw_error() exceptions.c:444 0x0016728c
37 memory_error() corefile.c:204 0x001d1fcc
36 read_memory() corefile.c:223 0x001d201a
35 read_memory_unsigned_integer() corefile.c:312 0x001d2166
34 arm_skip_prologue() arm-tdep.c:1452 0x00054270
33 gdbarch_skip_prologue() gdbarch.c:2603 0x00176e5c
32 skip_prologue_sal() symtab.c:2869 0x0013dad2
31 find_function_start_sal() symtab.c:2782 0x0013d9aa
30 symbol_to_sal() linespec.c:3622 0x0014f722
29 convert_linespec_to_sals() linespec.c:2028 0x0014d6fa
28 parse_linespec() linespec.c:2319 0x0014dc04
27 decode_line_full() linespec.c:2430 0x0014df44
26 parse_breakpoint_sals() breakpoint.c:9323 0x00108560
25 create_sals_from_address_default() breakpoint.c:14306 0x0010ec6e
24 bkpt_create_sals_from_address() breakpoint.c:13123 0x0010d736
23 create_breakpoint() breakpoint.c:9554 0x00108a6e
22 break_command_1() breakpoint.c:9772 0x00108ef0
21 break_command() breakpoint.c:9845 0x00109000
20 do_cfunc() cli-decode.c:113 0x000a4782
19 cmd_func() cli-decode.c:1859 0x000a669c
18 execute_command() top.c:484 0x0022299c
17 command_handler() event-top.c:431 0x0016fcac
16 command_line_handler() event-top.c:629 0x0017028e
15 rl_callback_read_char() callback.c:220 0x0026a9d2
14 rl_callback_read_char_wrapper() event-top.c:163 0x0016f880
13 stdin_event_handler() event-top.c:371 0x0016fba6
12 handle_file_event() event-loop.c:768 0x0016ec66
11 process_event() event-loop.c:342 0x0016e288
10 gdb_do_one_event() event-loop.c:406 0x0016e348
9 start_event_loop() event-loop.c:431 0x0016e38a
8 cli_command_loop() event-top.c:176 0x0016f8b2
7 current_interp_command_loop() interps.c:331 0x001685d8
6 captured_command_loop() main.c:258 0x00168e1c
5 catch_errors() exceptions.c:546 0x00167458
4 captured_main() main.c:1041 0x0016a19a
3 catch_errors() exceptions.c:546 0x00167458
2 gdb_main() main.c:1050 0x0016a1ca
1 main() gdb.c:34 0x0004f26c

I guess only way to address it is to either use the patch I have
posted or may be disable the test for arm? Any suggestions?

Thanks!