[PATCH] bfd: Fix GCC warning when CFLAGS="-Og" is used

[Jan Beulich]

On 04.09.2024 11:24, Shahab Vahedi wrote:
> From: Shahab Vahedi <shahab.vahedi@amd.com>
> 
> This patch initializes the "op" variable in skip_cfa_op() function
> of bfd/elf-eh-frame.c to "0" at its declaration point to avoid the
> "maybe-uninitialized" warning.
> 
> Building binutils on a system with GCC version 13.2.0 and a configure
> command that sets the optimization level to "-Og" leads to a build
> failure because of a warning being treated as an error:
> ---------------------------------------------------------------------
> $ ./configure CFLAGS="-Og"
> $ make
>   ...
>   CC       elf-eh-frame.lo
>   /src/gdb/bfd/elf-eh-frame.c: In function 'skip_cfa_op':
>   /src/gdb/bfd/elf-eh-frame.c:354:33: error: 'op' may be used
>     uninitialized [-Werror=maybe-uninitialized]
>   354 |   switch (op & 0xc0 ? op & 0xc0 : op)
>       |           ~~~~~~~~~~~~~~~~~~~~~~^~~~
>   /src/gdb/bfd/elf-eh-frame.c:348:12: note: 'op' was declared here
>   348 |   bfd_byte op;
>       |            ^~
>   cc1: all warnings being treated as errors
>   ...
> ---------------------------------------------------------------------
> 
> The relevant code snippet related to this warning looks like:
> ---------------------------------------------------------------------
>   static inline bool
>   read_byte (bfd_byte **iter, bfd_byte *end, unsigned char *result)
>   {
>     if (*iter >= end)
>       return false;
>     *result = *((*iter)++);
>     return true;
>   }
> 
>   static bool
>   skip_cfa_op (bfd_byte **iter, bfd_byte *end,...)
>   {
>     bfd_byte op;
> 
>     if (!read_byte (iter, end, &op))
>       return false;
> 
>     switch (op & 0xc0 ? op & 0xc0 : op)
>     ...
>   }
> ---------------------------------------------------------------------
> 
> This warning probably happens because "-Og" results in GCC not
> inlining the "read_byte()" function. Therefore, GCC treats its
> invocation inside "skip_cfa_op()" like a black box and that ends
> in the aforementioned warning.
> 
> Acknowledgement:
>   Lancelot Six -- for coming with the idea behind this fix.
> 
> bfd/ChangeLog:
> 	* elf-eh-frame.c (skip_cfa_op): Initialize the "op" variable.

Okay, yet preferably with ...

> --- a/bfd/elf-eh-frame.c
> +++ b/bfd/elf-eh-frame.c
> @@ -345,7 +345,7 @@ next_cie_fde_offset (const struct eh_cie_fde *ent,
>  static bool
>  skip_cfa_op (bfd_byte **iter, bfd_byte *end, unsigned int encoded_ptr_width)
>  {
> -  bfd_byte op;
> +  bfd_byte op = 0x00;

... simply "0" used here.

Jan