Re: [PATCH] Fix regression in pointer-to-member printing

[Joel Brobecker <brobecker@adacore.com>]

Hi Tom,

On Tue, Oct 18, 2022 at 11:53:04AM -0600, Tom Tromey via Gdb-patches wrote:
> PR c++/29243 points out that "info func" on a certain C++ executable
> will cause an infinite loop in gdb.
> 
> I tracked this down to a bug introduced by commit 6b5a7bc76 ("Handle
> member pointers directly in generic_value_print").  Before this
> commit, the C++ code to print a member pointer would wind up calling
> value_print_scalar_formatted; but afterward it simply calls
> generic_value_print and gets into a loop.

Thanks for the fix :-).

The patch looks good to me. Thanks also for including a regression
test!

> This patch restores the previous behavior and adds a regression test.
> ---
>  gdb/testsuite/gdb.cp/member-ptr.cc  | 8 ++++++++
>  gdb/testsuite/gdb.cp/member-ptr.exp | 4 ++++
>  gdb/valprint.c                      | 2 +-
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/testsuite/gdb.cp/member-ptr.cc b/gdb/testsuite/gdb.cp/member-ptr.cc
> index 22ffcc58d39..a563d2e6af3 100644
> --- a/gdb/testsuite/gdb.cp/member-ptr.cc
> +++ b/gdb/testsuite/gdb.cp/member-ptr.cc
> @@ -142,6 +142,11 @@ int Diamond::vget_base ()
>    return this->Left::x + 2000;
>  }
>  
> +struct Container
> +{
> +  PMI member;
> +};
> +
>  int
>  func (int x)
>  {
> @@ -205,6 +210,9 @@ int main ()
>    null_pmi = NULL;
>    null_pmf = NULL;
>  
> +  Container contain;
> +  contain.member = &A::j;
> +
>    pmi = NULL; /* Breakpoint 1 here.  */
>  
>    (diamond.*diamond_pfunc_ptr) (20);
> diff --git a/gdb/testsuite/gdb.cp/member-ptr.exp b/gdb/testsuite/gdb.cp/member-ptr.exp
> index 110497b893b..5b91bcb493a 100644
> --- a/gdb/testsuite/gdb.cp/member-ptr.exp
> +++ b/gdb/testsuite/gdb.cp/member-ptr.exp
> @@ -628,3 +628,7 @@ gdb_test "print null_pmi = 0" "$vhn = NULL"
>  gdb_test "print null_pmf" "$vhn = NULL"
>  gdb_test "print null_pmf = &A::foo" "$vhn = \\(int \\(A::\\*\\)\\(A \\*( const)?, int\\)\\) $hex <A::foo ?\\(int\\)>"
>  gdb_test "print null_pmf = 0" "$vhn = NULL"
> +
> +# Print with a format, bypassing the direct call to the scalar
> +# printer.  See PR c++/29243.
> +gdb_test "print/x contain" " = {member = $hex}"
> diff --git a/gdb/valprint.c b/gdb/valprint.c
> index f079f31fa7b..585af69cb27 100644
> --- a/gdb/valprint.c
> +++ b/gdb/valprint.c
> @@ -879,7 +879,7 @@ generic_value_print_memberptr
>        cp_print_class_member (valaddr, type, stream, "&");
>      }
>    else
> -    generic_value_print (val, stream, recurse, options, decorations);
> +    value_print_scalar_formatted (val, options, 0, stream);
>  }
>  
>  /* See valprint.h.  */
> -- 
> 2.34.3
> 

-- 
Joel