[Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Roy Kollen Svendsen]

readline builds its shared library without linking the curses/termcap
library, so termcap symbols (UP, BC, PC) are left undefined.

host-gdb pulls in host-readline, installing this libreadline.so into the
host directory. buildroot runs its fakeroot finalization script with
/bin/sh, and fakeroot puts $(HOST_DIR)/lib in LD_LIBRARY_PATH; so when
/bin/sh is linked against readline (e.g. bash) it loads this host
libreadline.so rather than the system one, and because UP is a data
symbol the loader aborts before /bin/sh can start:

  /bin/sh: symbol lookup error: libreadline.so.8: undefined symbol: UP

This only happens when the host's /bin/sh links readline and host-gdb is
enabled; otherwise the host libreadline.so is never loaded, which is why
it is not seen on every build host.

Pass SHLIB_LIBS so readline's own build links the host shared library
against the libncursesw that host-ncurses already provides (it carries
the termcap symbols), making the host libreadline.so self-contained.
Only the host library is changed: the target library is never loaded
during the build, so it cannot break image generation.

Fixes: d98e15a3639d ("package/gdb: really fix build with GCC 15.x by using external readline")
Signed-off-by: Roy Kollen Svendsen <roykollensvendsen@gmail.com>
---
 package/readline/readline.mk | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/package/readline/readline.mk b/package/readline/readline.mk
index f69cbe45e2..99d3711e7b 100644
--- a/package/readline/readline.mk
+++ b/package/readline/readline.mk
@@ -30,5 +30,14 @@ define READLINE_INSTALL_INPUTRC
 endef
 READLINE_POST_INSTALL_TARGET_HOOKS += READLINE_INSTALL_INPUTRC
 
+# readline does not link its shared library against the curses/termcap
+# library, leaving termcap symbols (UP, BC, PC) undefined. fakeroot runs
+# its finalization script with $(HOST_DIR)/lib in LD_LIBRARY_PATH, so a
+# readline-linked /bin/sh loads this host libreadline.so during root
+# filesystem generation and aborts on the undefined symbols. Link it
+# against the libncursesw that host-ncurses provides (it carries those
+# symbols) via readline's SHLIB_LIBS.
+HOST_READLINE_MAKE_OPTS += SHLIB_LIBS="-L$(HOST_DIR)/lib -lncursesw"
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))
-- 
2.54.0

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Re: [Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Alexander Sverdlin]

Hi Roy,

thanks for looking into this!
I've just stubled upon the same issue, however...

On Tue, 2026-06-02 at 13:47 +0200, Roy Kollen Svendsen wrote:
> readline builds its shared library without linking the curses/termcap
> library, so termcap symbols (UP, BC, PC) are left undefined.
> 
> host-gdb pulls in host-readline, installing this libreadline.so into the
> host directory. buildroot runs its fakeroot finalization script with
> /bin/sh, and fakeroot puts $(HOST_DIR)/lib in LD_LIBRARY_PATH; so when
> /bin/sh is linked against readline (e.g. bash) it loads this host
> libreadline.so rather than the system one, and because UP is a data
> symbol the loader aborts before /bin/sh can start:
> 
>   /bin/sh: symbol lookup error: libreadline.so.8: undefined symbol: UP
> 
> This only happens when the host's /bin/sh links readline and host-gdb is
> enabled; otherwise the host libreadline.so is never loaded, which is why
> it is not seen on every build host.
> 
> Pass SHLIB_LIBS so readline's own build links the host shared library
> against the libncursesw that host-ncurses already provides (it carries
> the termcap symbols), making the host libreadline.so self-contained.
> Only the host library is changed: the target library is never loaded
> during the build, so it cannot break image generation.
> 
> Fixes: d98e15a3639d ("package/gdb: really fix build with GCC 15.x by using external readline")

One can argue that the problem was introduced even earlier by commit
baa81362ef ("package/readline: Use configure options to link with ncurses"),
but wasn't triggered until d98e15a3639d...

> Signed-off-by: Roy Kollen Svendsen <roykollensvendsen@gmail.com>
> ---
>  package/readline/readline.mk | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/package/readline/readline.mk b/package/readline/readline.mk
> index f69cbe45e2..99d3711e7b 100644
> --- a/package/readline/readline.mk
> +++ b/package/readline/readline.mk
> @@ -30,5 +30,14 @@ define READLINE_INSTALL_INPUTRC
>  endef
>  READLINE_POST_INSTALL_TARGET_HOOKS += READLINE_INSTALL_INPUTRC
>  
> +# readline does not link its shared library against the curses/termcap
> +# library, leaving termcap symbols (UP, BC, PC) undefined. fakeroot runs
> +# its finalization script with $(HOST_DIR)/lib in LD_LIBRARY_PATH, so a
> +# readline-linked /bin/sh loads this host libreadline.so during root
> +# filesystem generation and aborts on the undefined symbols. Link it
> +# against the libncursesw that host-ncurses provides (it carries those
> +# symbols) via readline's SHLIB_LIBS.
> +HOST_READLINE_MAKE_OPTS += SHLIB_LIBS="-L$(HOST_DIR)/lib -lncursesw"

This assumes that host-ncurses always builds the wide variant... Should we
just mimic commit baa81362ef instead? Something like

HOST_READLINE_CONF_ENV = $(READLINE_CONF_ENV)
HOST_READLINE_CONF_OPTS = $(READLINE_CONF_OPTS)

?

> +
>  $(eval $(autotools-package))
>  $(eval $(host-autotools-package))

-- 
Alexander Sverdlin.
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Re: [Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Thomas Petazzoni via buildroot]

On Sun, Oct 11, 2026 at 10:28:11AM +0200, Alexander Sverdlin wrote:

> This assumes that host-ncurses always builds the wide variant... Should we
> just mimic commit baa81362ef instead? Something like
> 
> HOST_READLINE_CONF_ENV = $(READLINE_CONF_ENV)
> HOST_READLINE_CONF_OPTS = $(READLINE_CONF_OPTS)

I don't have the full context, but doing this is almost always a bad
idea. It easily breaks as people change target variable (CONF_ENV,
CONF_OPTS) without realizing it also affects the host package.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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Re: [Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Alexander Sverdlin]

Hi Thomas,

On Sun, 2026-10-11 at 10:50 +0200, Thomas Petazzoni wrote:
> > This assumes that host-ncurses always builds the wide variant... Should we
> > just mimic commit baa81362ef instead? Something like
> > 
> > HOST_READLINE_CONF_ENV = $(READLINE_CONF_ENV)
> > HOST_READLINE_CONF_OPTS = $(READLINE_CONF_OPTS)
> 
> I don't have the full context, but doing this is almost always a bad
> idea. It easily breaks as people change target variable (CONF_ENV,
> CONF_OPTS) without realizing it also affects the host package.

we might want to copy-paste both variables as well; in any case, maybe we
want to rely on configure figuring out ncurses deps instead of mangling
configure result on make step.

-- 
Alexander Sverdlin.
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Re: [Buildroot] [PATCH] package/readline: link host shared library against ncurses

[Arnout Vandecappelle via buildroot]

  Hi Roy,

On 02/06/2026 13:47, Roy Kollen Svendsen wrote:
> readline builds its shared library without linking the curses/termcap
> library, so termcap symbols (UP, BC, PC) are left undefined.

  We can achieve the same, I think, by setting

HOST_READLINE_CONF_OPTS = --with-curses --with-shared-termcap-library

(which is what we do on the target). That would be much simpler and more 
understandle.

  Regards,
  Arnout

> host-gdb pulls in host-readline, installing this libreadline.so into the
> host directory. buildroot runs its fakeroot finalization script with
> /bin/sh, and fakeroot puts $(HOST_DIR)/lib in LD_LIBRARY_PATH; so when
> /bin/sh is linked against readline (e.g. bash) it loads this host
> libreadline.so rather than the system one, and because UP is a data
> symbol the loader aborts before /bin/sh can start:
> 
>    /bin/sh: symbol lookup error: libreadline.so.8: undefined symbol: UP
> 
> This only happens when the host's /bin/sh links readline and host-gdb is
> enabled; otherwise the host libreadline.so is never loaded, which is why
> it is not seen on every build host.
> 
> Pass SHLIB_LIBS so readline's own build links the host shared library
> against the libncursesw that host-ncurses already provides (it carries
> the termcap symbols), making the host libreadline.so self-contained.
> Only the host library is changed: the target library is never loaded
> during the build, so it cannot break image generation.
> 
> Fixes: d98e15a3639d ("package/gdb: really fix build with GCC 15.x by using external readline")
> Signed-off-by: Roy Kollen Svendsen <roykollensvendsen@gmail.com>
> ---
>   package/readline/readline.mk | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/package/readline/readline.mk b/package/readline/readline.mk
> index f69cbe45e2..99d3711e7b 100644
> --- a/package/readline/readline.mk
> +++ b/package/readline/readline.mk
> @@ -30,5 +30,14 @@ define READLINE_INSTALL_INPUTRC
>   endef
>   READLINE_POST_INSTALL_TARGET_HOOKS += READLINE_INSTALL_INPUTRC
>   
> +# readline does not link its shared library against the curses/termcap
> +# library, leaving termcap symbols (UP, BC, PC) undefined. fakeroot runs
> +# its finalization script with $(HOST_DIR)/lib in LD_LIBRARY_PATH, so a
> +# readline-linked /bin/sh loads this host libreadline.so during root
> +# filesystem generation and aborts on the undefined symbols. Link it
> +# against the libncursesw that host-ncurses provides (it carries those
> +# symbols) via readline's SHLIB_LIBS.
> +HOST_READLINE_MAKE_OPTS += SHLIB_LIBS="-L$(HOST_DIR)/lib -lncursesw"
> +
>   $(eval $(autotools-package))
>   $(eval $(host-autotools-package))

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