[Bug c/78512] [7 Regression] r242674 miscompiles Linux kernel

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78512

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2016-11-24
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
I have yet to look into the details of this issue but just a quick clarifying
comment:

-fprintf-return-value is almost entirely based on the C requirements, with the
exception of %p where it does make use of its knowledge of the underlying
implementation.  The option cannot match a non-conforming implementation
without a corresponding target hook that describes it so when one is being
targeted the options should not be used  The option should be disabled
automatically when either -fno-builtin-sprintf or its equivalent such
-ffreestanding is specified (if it isn't it's a bug).

That said, I don't think the Linux kernel uses either of these options.  That
suggests that the Linux printf should be conforming and the miscompilation may
be a bug.  Otherwise, it the Linux printf isn't conforming and we want it to
benefit from the option (as I would expect us to since the request for the
related -Wformat-length warning came from someone either contributing to or
building the kernel) GCC might want to add a target hook describing the Linux
printf specifics and a new option and to let the kernel enable it.