Re: [PATCH] Increase size of main_type::nfields

[Simon Marchi <simark@simark.ca>]

On 1/11/23 15:44, Tom Tromey via Gdb-patches wrote:
> main_type::nfields is a 'short', and has been for many years.  PR
> c++/29985 points out that 'short' is too narrow for an enum that
> contains more than 2^15 constants.
> 
> This patch bumps the size of 'nfields'.  To verify that the field
> isn't directly used, it is also renamed.  Note that this does not
> affect the size of main_type on x86-64 Fedora 36.  And, if it does
> have a negative effect somewhere, it's worth considering that types
> could be shrunk more drastically by using subclasses for the different
> codes.
> 
> I wasn't sure whether a test case for this would be desirable.  It
> would be a bit large.

We could make a test case that generates a source file on the fly in
standard_output_directory and compiles it.

> ---
>  gdb/gdb-gdb.py.in | 4 ++--
>  gdb/gdbtypes.h    | 6 +++---
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/gdb/gdb-gdb.py.in b/gdb/gdb-gdb.py.in
> index dbc4d773e0b..95b7d84966f 100644
> --- a/gdb/gdb-gdb.py.in
> +++ b/gdb/gdb-gdb.py.in
> @@ -261,8 +261,8 @@ class StructMainTypePrettyPrinter:
>          fields.append("flags = [%s]" % self.flags_to_string())
>          fields.append("owner = %s" % self.owner_to_string())
>          fields.append("target_type = %s" % self.val["m_target_type"])
> -        if self.val["nfields"] > 0:
> -            for fieldno in range(self.val["nfields"]):
> +        if self.val["m_nfields"] > 0:
> +            for fieldno in range(self.val["m_nfields"]):
>                  fields.append(self.struct_field_img(fieldno))
>          if self.val["code"] == gdb.TYPE_CODE_RANGE:
>              fields.append(self.bounds_img())
> diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
> index a9abb0d8071..da1d0f79d1f 100644
> --- a/gdb/gdbtypes.h
> +++ b/gdb/gdbtypes.h
> @@ -836,7 +836,7 @@ struct main_type
>    /* * Number of fields described for this type.  This field appears
>       at this location because it packs nicely here.  */
>  
> -  short nfields;
> +  int m_nfields;

Should it be unsigned?  I don't recall this field needing to be
negative.

Otherwise, LGTM.

Simon