Re: -Werror enabled by default on GNU/Hurd

* Andrea Monaco via Gdb <[email protected]> [2021-12-29 19:06:04 +0100]:

> 
>   > with this patch I am now able to build GDB on GNU/Hurd (i686).  This
>   > might help you out.
> 
> Thanks, that solves a warning.  But the build still fails with this
> output:
> 
> 
>   CXX    msg_U.o
> cc1: warning: command-line option '-Wno-mismatched-tags' is valid for C++/ObjC++ but not for C
> cc1: warning: command-line option '-Wsuggest-override' is valid for C++/ObjC++ but not for C
> cc1: warning: command-line option '-Wdeprecated-copy' is valid for C++/ObjC++ but not for C
> cc1: warning: command-line option '-Wdeprecated-copy-dtor' is valid for C++/ObjC++ but not for C
> cc1: warning: command-line option '-Wredundant-move' is valid for C++/ObjC++ but not for C
> cc1: warning: command-line option '-Wstrict-null-sentinel' is valid for C++/ObjC++ but not for C
> msg_U.c: In function 'msg_set_init_ports':
> msg_U.c:1044:22: error: conversion from 'unsigned int' to 'short unsigned int' changes value from '4294967295' to '65535' [-Werror=overflow]
>  1044 |   /* msgtl_name = */ MACH_MSG_TYPE_POLYMORPHIC,
>       |                      ^~~~~~~~~~~~~~~~~~~~~~~~~
> msg_U.c: In function 'msg_set_dtable':
> msg_U.c:1838:22: error: conversion from 'unsigned int' to 'short unsigned int' changes value from '4294967295' to '65535' [-Werror=overflow]
>  1838 |   /* msgtl_name = */ MACH_MSG_TYPE_POLYMORPHIC,
>       |                      ^~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> Makefile:1684: recipe for target 'msg_U.o' failed
> make: *** [msg_U.o] Error 1

I don't claim to know anything about GNU/Hurd, this was the first time
I ever installed it.

The file msg_U.c is generated using the mig tool, and the .defs files
binutils-gdb/gdb/msg.defs.  The .defs file just includes
/usr/include/hurd/msg.h.  And the makefile fragment that builds the
msg_U.c is found in binutils-gdb/gdb/config/i386/i386gnu.mn.

I notice in the above, that my version of those two lines is slightly
different, like this:

  /* msgtl_name = */      (unsigned short) MACH_MSG_TYPE_POLYMORPHIC,

Which would solve the error you're seeing.  Finally, here's the
version number information for the mig tool I'm using:

  $ mig --version
  i686-gnu-mig (GNU MIG) 1.8+git20200618

Remembering that you probably understand all this far better than me,
I wonder if you need to update your version of mig?

As a last resort if you patch your generated file, adding the cast
that I see, is this enough to finish building GDB?  Clearly this isn't
a long term solution, but it feels like the above warning is a tooling
issue, rather than a problem with the GDB source.

Thanks,
Andrew