Re: [PATCH] gdb: Fix -Wuninitialied issue

[Tom de Vries via Gdb-patches <gdb-patches@sourceware.org>]

On 9/12/23 10:22, Enze Li wrote:
> I see the following warning when building GDB on FreeBSD/amd64 with
> Clang 14,
> 
> ======================================================================
>    CXX    mdebugread.o
> mdebugread.c:1069:3: error: variable 'f' is uninitialized when used here [-Werror,-Wuninitialized]
>                  f->set_loc_enumval (tsym.value);
>                  ^
> mdebugread.c:836:17: note: initialize the variable 'f' to silence this warning
>          struct field *f;
>                         ^
>                          = nullptr
> ======================================================================
> 
> after digging a little, I realized that we can not simply do what
> Clang 14 says.
> 
> The root cause of this issue is that we lost the initialization of
> the variable 'f' in this commit,
> 
>    commit 2774f2dad5f05e68771c07df6ab0fb23baa2118e
>    Date:   Thu Aug 31 09:37:44 2023 +0200
> 
>        [gdb/symtab] Factor out type::{alloc_fields,copy_fields}
> 

Hi,

thanks for fixing this.  I've reviewed my commit once more, and only 
found the instance that this patch fixes.

LGTM.

Approved-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom

> we have made these modifications,
> 
> ----------------------------------------------------------------------
> --- a/gdb/mdebugread.c
> +++ b/gdb/mdebugread.c
> @@ -1034,9 +1034,7 @@ parse_symbol (SYMR *sh, union aux_ext *ax, char *ext_sh, int bigend,
> 
>          t->set_code (type_code);
>          t->set_length (sh->value);
> -       t->set_num_fields (nfields);
> -       f = ((struct field *) TYPE_ALLOC (t, nfields * sizeof (struct field)));
> -       t->set_fields (f);
> +       t->alloc_fields (nfields, false);
> ----------------------------------------------------------------------
> 
> The problem is that the variable 'f' is used in the second half of
> parse_symbol, that's why Clang complained.
> 
> To fix this issue we need to ensure that the varibale 'f' is
> initialized.  Calling the fields method is an obvious way to fix this
> issue.
> 
> Tested on FreeBSD/amd64 by rebuilding.
> ---
>   gdb/mdebugread.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/gdb/mdebugread.c b/gdb/mdebugread.c
> index ea3e15be53b2..9cb30ce0acd0 100644
> --- a/gdb/mdebugread.c
> +++ b/gdb/mdebugread.c
> @@ -1035,6 +1035,7 @@ parse_symbol (SYMR *sh, union aux_ext *ax, char *ext_sh, int bigend,
>   	t->set_code (type_code);
>   	t->set_length (sh->value);
>   	t->alloc_fields (nfields);
> +	f = t->fields();
>   
>   	if (type_code == TYPE_CODE_ENUM)
>   	  {
> 
> base-commit: 318d3bda5cad124bd11eebb0349d0f183ba625b1