RE: [PATCH] Enable building GDB without installed libtermcap

[Bernd Edlinger <bernd dot edlinger at hotmail dot de>]

Hi,

ping...

patch looks good for me.


On Thu, 26 Feb 2015 19:14:41, Pedro Alves wrote:
>
> On 02/26/2015 06:55 PM, Eli Zaretskii wrote:
>>> From: Pedro Alves <palves@redhat.com>
>>> Given that this stub file never needed these variables while it was
>>> Windows-only, how about we simply not define the variables if
>>> compiling for mingw/cygwin, but define them as weak everywhere else?
>>
>> Works for me, thanks.
>
> Alright. I recalled that Cygwin doesn't really care about old gcc's,
> so I filed it under not-a-problem and limited the #ifdefery to mingw.
>
> I'd like to hear more opinions on this (whole thing) before
> pushing ahead.
>
> From b99d25c7fc2b10d93b51743f44c08558bf06dfd6 Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Thu, 26 Feb 2015 17:01:06 +0000
> Subject: [PATCH] Fallback to stub-termcap.c on all hosts
>
> Currently building gdb is impossible without an installed termcap or
> curses library. But, GDB already has a very minimal termcap in the
> tree to handle this situation for Windows -- gdb/stub-termcap.c. This
> patch makes that the fallback for all hosts.
>
> Testing this on GNU/Linux (by simply hacking away the termcap/curses
> detection in gdb/configure.ac), I tripped on:
>
> ../readline/libreadline.a(terminal.o): In function `_rl_init_terminal_io':
> /home/pedro/gdb/mygit/src/readline/terminal.c:527: undefined reference to `PC'
> /home/pedro/gdb/mygit/src/readline/terminal.c:528: undefined reference to `BC'
> /home/pedro/gdb/mygit/src/readline/terminal.c:529: undefined reference to `UP'
> /home/pedro/gdb/mygit/src/readline/terminal.c:538: undefined reference to `PC'
> /home/pedro/gdb/mygit/src/readline/terminal.c:539: undefined reference to `BC'
> /home/pedro/gdb/mygit/src/readline/terminal.c:540: undefined reference to `UP'
>
> These are globals that are normally defined by termcap (or ncurses'
> termcap emulation).
>
> Now, we could just define replacements in stub-termcap.c, but
> readline/terminal.c (at least the copy in our tree) has this "beauty":
>
> #if !defined (__linux__) && !defined (NCURSES_VERSION)
> # if defined (__EMX__) || defined (NEED_EXTERN_PC)
> extern
> # endif /* __EMX__ || NEED_EXTERN_PC */
> char PC, *BC, *UP;
> #endif /* !__linux__ && !NCURSES_VERSION */
>
> which can result in readline defining the globals too. That will
> usually work out in C, given that "-fcommon" is usually the default
> for C compilers, but that won't work for C++, or C with -fno-common
> (link fails with "multiple definition" errors)...
>
> Mirroring those #ifdef conditions in the stub termcap screams
> "brittle" to me -- I can see them changing in latter readline
> versions.
>
> My idea to work around that is to simply use __attribute__((weak)).
> Of all supported hosts
> (https://sourceware.org/gdb/wiki/Systems#Supported_Hosts), except Windows.
>
> Windows/PE/COFF's do support weak, but not on gcc 3.4 based toolchains
> (4.8.x does work). Given the file never needed the variables while it
> was Windows-only, just continue not defining them there.
>
> gdb/ChangeLog:
> 2015-02-26 Bernd Edlinger <bernd.edlinger@hotmail.de>
> Pedro Alves <palves@redhat.com>
>
> * configure.ac: Remove the mingw32-specific stub-termcap.o
> fallback, and instead fallback to the stub termcap on all hosts.
> * configure: Regenerate.
> * stub-termcap.c (PC, BC, UP): Define as weak symbols.
> ---
> gdb/configure.ac | 7 +------
> gdb/stub-termcap.c | 21 ++++++++++++++++++++-
> 2 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/gdb/configure.ac b/gdb/configure.ac
> index 6ac8adb..79fc115 100644
> --- a/gdb/configure.ac
> +++ b/gdb/configure.ac
> @@ -610,18 +610,13 @@ case $host_os in
> go32* | *djgpp*)
> ac_cv_search_tgetent="none required"
> ;;
> - *mingw32*)
> - if test x"$curses_found" != xyes; then
> - ac_cv_search_tgetent="none required"
> - CONFIG_OBS="$CONFIG_OBS stub-termcap.o"
> - fi ;;
> esac
>
> # These are the libraries checked by Readline.
> AC_SEARCH_LIBS(tgetent, [termcap tinfo curses ncurses])
>
> if test "$ac_cv_search_tgetent" = no; then
> - AC_MSG_ERROR([no termcap library found])
> + CONFIG_OBS="$CONFIG_OBS stub-termcap.o"
> fi
>
> AC_ARG_WITH([system-readline],
> diff --git a/gdb/stub-termcap.c b/gdb/stub-termcap.c
> index cc8632c..df5f888 100644
> --- a/gdb/stub-termcap.c
> +++ b/gdb/stub-termcap.c
> @@ -32,9 +32,28 @@ extern char* tgetstr (char *name, char **area);
> extern int tputs (char *string, int nlines, int (*outfun) ());
> extern char *tgoto (const char *cap, int col, int row);
>
> +/* These globals below are global termcap variables that readline
> + references.
> +
> + Actually, depending on preprocessor conditions that we don't want
> + to mirror here (as they may change depending on readline versions),
> + readline may define these globals as well, relying on the linker
> + merging them if needed (-fcommon). That doesn't work with
> + -fno-common or C++, so instead we define the symbols as weak.
> + Don't do this on Windows though, as MinGW gcc 3.4.2 doesn't support
> + weak (later versions, e.g., 4.8, do support it). Given this stub
> + file originally was Windows only, and we only needed this when we
> + made it work on other hosts, it should be OK. */
> +#ifndef __MINGW32__
> +char PC __attribute__((weak));
> +char *BC __attribute__((weak));
> +char *UP __attribute__((weak));
> +#endif
> +
> /* Each of the files below is a minimal implementation of the standard
> termcap function with the same name, suitable for use in a Windows
> - console window. */
> + console window, or when a real termcap/curses library isn't
> + available. */
>
> int
> tgetent (char *buffer, char *termtype)
> --
> 1.9.3
>
>