Re: [PATCH] Fix build with GCC 7.5

[Tom de Vries <tdevries@suse.de>]

On 11/22/23 16:17, Tom Tromey wrote:
> Tom> This fixes one of the three warnings.
> 
> Indeed, duh.  Sorry about that.
> 
> Here is v2.
> 

With this patch I was able to finish the build using system gcc 7.5.0.

Thanks,
- Tom

> Tom
> 
> commit 0447f3d09267f6fb90237b42aa6e1ec137a09c87
> Author: Tom Tromey <tromey@adacore.com>
> Date:   Wed Nov 22 06:54:40 2023 -0700
> 
>      Fix build with GCC 7.5
>      
>      A recent change to 'struct field' caused a build failure with GCC
>      7.5.0, as reported by Tom de Vries:
>      
>      /data/vries/gdb/src/gdb/gdbtypes.h:721:51: error:
>      ‘field::m_accessibility’ is too small to hold all values of ‘enum
>      class accessibility’ [-Werror]
>         ENUM_BITFIELD (accessibility) m_accessibility : 2;
>                                                         ^
>      
>      Mark Wielaard pointed out that this was a GCC bug:
>      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51242
>      
>      This patch works around the bug by changing several members not to be
>      bitfields.  It reduces the size of the enum's underlying type,
>      instead.
>      
>      I also changed m_bitsize to no longer be a bitfield -- that was done
>      for packing reasons in ancient times, but with m_accessibility not
>      being a bitfield, this no longer matters.
>      
>      I removed fn_field::dummy.  In earlier times it was somewhat normal in
>      gdb to have these dummy fields to keep track of any available padding.
>      However, since the advent of "ptype/o", there doesn't seem to be any
>      need for this.
>      
>      This patch does not change the size of struct field, fn_field, or
>      decl_field on 64-bit hosts.
> 
> diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
> index 34ca1ac99e5..eca92196364 100644
> --- a/gdb/gdbtypes.h
> +++ b/gdb/gdbtypes.h
> @@ -534,7 +534,7 @@ union field_location
>   };
>   
>   /* Accessibility of a member.  */
> -enum class accessibility : unsigned
> +enum class accessibility : unsigned char
>   {
>     /* It's important that this be 0 so that fields default to
>        public.  */
> @@ -717,8 +717,6 @@ struct field
>   
>     unsigned int m_artificial : 1;
>   
> -  /* Accessibility of the field.  */
> -  ENUM_BITFIELD (accessibility) m_accessibility : 2;
>     /* Whether the field is 'virtual'.  */
>     bool m_virtual : 1;
>     /* Whether the field is 'ignored'.  */
> @@ -728,13 +726,16 @@ struct field
>   
>     ENUM_BITFIELD(field_loc_kind) m_loc_kind : 3;
>   
> +  /* Accessibility of the field.  */
> +  enum accessibility m_accessibility;
> +
>     /* * Size of this field, in bits, or zero if not packed.
>        If non-zero in an array type, indicates the element size in
>        bits (used only in Ada at the moment).
>        For an unpacked field, the field's type's length
>        says how many bytes the field occupies.  */
>   
> -  unsigned int m_bitsize : 28;
> +  unsigned int m_bitsize;
>   
>     /* * In a struct or union type, type of this field.
>        - In a function or member type, type of this argument.
> @@ -1611,8 +1612,6 @@ struct fn_field
>   
>     unsigned int is_const:1;
>     unsigned int is_volatile:1;
> -  /* Accessibility of the field.  */
> -  ENUM_BITFIELD (accessibility) accessibility : 2;
>     unsigned int is_artificial:1;
>   
>     /* * A stub method only has some fields valid (but they are enough
> @@ -1633,9 +1632,8 @@ struct fn_field
>   
>     ENUM_BITFIELD (dwarf_defaulted_attribute) defaulted : 2;
>   
> -  /* * Unused.  */
> -
> -  unsigned int dummy:6;
> +  /* Accessibility of the field.  */
> +  enum accessibility accessibility;
>   
>     /* * Index into that baseclass's virtual function table, minus 2;
>        else if static: VOFFSET_STATIC; else: 0.  */
> @@ -1658,7 +1656,7 @@ struct decl_field
>     struct type *type;
>   
>     /* Accessibility of the field.  */
> -  ENUM_BITFIELD (accessibility) accessibility : 2;
> +  enum accessibility accessibility;
>   };
>   
>   /* * C++ language-specific information for TYPE_CODE_STRUCT and