Re: [PATCH] Fix unitialized warning on gdb/typeprint.c:whatis_exp

[Pedro Alves <palves@redhat.com>]

On 01/16/2018 08:32 PM, Sergio Durigan Junior wrote:
> This simple patch initializes "struct value *val" to NULL, which
> silences a when compiling GDB with certain GCC versions.

Please include a representative paste of warnings in git logs.
It makes it easier to see what a patch/commit is about.

> This warning is technically incorrect, because there is now way that
> "val" will be used unitialized if you look at the code flow, but it's
> a simple "fix" and doesn't do any harm.

No, it's not incorrect.  It's showing a real bug.  Try, e.g.:

(gdb) set print object on
(gdb) whatis some_structure_type

Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
0x00000000005dda90 in check_typedef (type=0x6120736573756170) at src/gdb/gdbtypes.c:2388
2388      int instance_flags = TYPE_INSTANCE_FLAGS (type);
(top-gdb) bt
#0  0x00000000005dda90 in check_typedef(type*) (type=0x6120736573756170) at src/gdb/gdbtypes.c:2388
#1  0x00000000005e63fb in gnuv3_rtti_type(value*, int*, LONGEST*, int*) (value=0xdf21b7, full_p=0x7fffffffd180, top_p=0x7fffffffd188, using_enc_p=0x7fffffffd184) at src/gdb/gnu-v3-abi.c:293
#2  0x000000000055f7d8 in value_rtti_type(value*, int*, long*, int*) (v=0xdf21b7, full=0x7fffffffd180, top=0x7fffffffd188, using_enc=0x7fffffffd184) at src/gdb/cp-abi.c:117
#3  0x00000000006cc61f in whatis_exp(char const*, int) (exp=<optimized out>, show=-1) at src/gdb/typeprint.c:515
#4  0x0000000000472462 in cmd_func(cmd_list_element*, char const*, int) (cmd=<optimized out>, args=<optimized out>, from_tty=<optimized out>)
    at src/gdb/cli/cli-decode.c:1886
#5  0x00000000006b833a in execute_command(char const*, int) (p=<optimized out>, from_tty=1) at src/gdb/top.c:630
#6  0x00000000005c0f8c in command_handler(char const*) (command=0xdf21b0 "whatis siginfo_t") at src/gdb/event-top.c:583
#7  0x00000000005c12d8 in command_line_handler(char*) (rl=<optimized out>) at /home/pedro/gdb/mygit/src/gdb/event-top.c:774
...

Thanks,
Pedro Alves