Re: [PATCH] Fix "unset local-environment" when clearenv not available

[Tom de Vries <tdevries@suse.de>]

On 12/10/25 5:24 PM, Tom Tromey wrote:
> Tom de Vries pointed out that clearenv isn't available on all hosts.
> Since this seems like a niche command at best, it seemed fine to
> disable this command on such platforms.

Hi Tom,

thanks for fixing this.

I've applied this patch to the cross-build setup 
(--host=x86_64-w64-mingw32) where I ran into this problem, and it fixes 
the build.

I've also applied it to an x86_64-linux build, and ran the test-case 
using make-check-all.sh.

There is one failure with remote host configuration:
...
FAIL: gdb.base/local-env.exp: show environment displayed variable
...
because that relies on setenv, but that's a pre-existing problem.

[ I came across this here ( 
https://man7.org/linux/man-pages/man3/clearenv.3.html ):
...
On systems where clearenv() is unavailable, the assignment

            environ = NULL;

        will probably do.
...
but I think that the disable-command approach is safer. ]

LGTM.

Reviewed-By: Tom de Vries <tdevries@suse.de>

Thanks,
- Tom

> ---
>   gdb/config.in                        |  3 +++
>   gdb/configure                        |  1 +
>   gdb/configure.ac                     |  1 +
>   gdb/infcmd.c                         | 15 ++++++++++++++-
>   gdb/testsuite/gdb.base/local-env.exp | 24 +++++++++++++++++++-----
>   5 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/gdb/config.in b/gdb/config.in
> index 9e2bba42e28..62d9e0eda6d 100644
> --- a/gdb/config.in
> +++ b/gdb/config.in
> @@ -110,6 +110,9 @@
>      the CoreFoundation framework. */
>   #undef HAVE_CFPREFERENCESCOPYAPPVALUE
>   
> +/* Define to 1 if you have the `clearenv' function. */
> +#undef HAVE_CLEARENV
> +
>   /* Define if compiling support to gdb compile. */
>   #undef HAVE_COMPILE
>   
> diff --git a/gdb/configure b/gdb/configure
> index cc446c6e4c8..dcf4fee40dd 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -30123,6 +30123,7 @@ $as_echo "#define AC_APPLE_UNIVERSAL_BUILD 1" >>confdefs.h
>   
>   for ac_func in  \
>     btowc \
> +  clearenv \
>     getgid \
>     getpgid \
>     getrlimit \
> diff --git a/gdb/configure.ac b/gdb/configure.ac
> index 1b9939b0754..3f44d9e684b 100644
> --- a/gdb/configure.ac
> +++ b/gdb/configure.ac
> @@ -1458,6 +1458,7 @@ AC_C_BIGENDIAN
>   
>   AC_CHECK_FUNCS([ \
>     btowc \
> +  clearenv \
>     getgid \
>     getpgid \
>     getrlimit \
> diff --git a/gdb/infcmd.c b/gdb/infcmd.c
> index 3ba286738a0..ed4fb819faf 100644
> --- a/gdb/infcmd.c
> +++ b/gdb/infcmd.c
> @@ -2146,12 +2146,25 @@ unset_var_in_environment (gdb_environ *env, const char *var, int from_tty)
>   {
>     if (var == 0)
>       {
> +      /* If there is no clearenv, don't bother asking the question.  */
> +#ifndef HAVE_CLEARENV
> +      if (env == nullptr)
> +	from_tty = 0;
> +#endif
> +
>         /* If there is no argument, delete all environment variables.
>   	 Ask for confirmation if reading from the terminal.  */
>         if (!from_tty || query (_("Delete all environment variables? ")))
>   	{
> +	  /* This was handled above.  */
>   	  if (env == nullptr)
> -	    clearenv ();
> +	    {
> +#ifdef HAVE_CLEARENV
> +	      clearenv ();
> +#else
> +	      error (_("Cannot clear the local environment on this host."));
> +#endif
> +	    }
>   	  else
>   	    env->clear ();
>   	}
> diff --git a/gdb/testsuite/gdb.base/local-env.exp b/gdb/testsuite/gdb.base/local-env.exp
> index fedcf9bc3e4..5bb639e2842 100644
> --- a/gdb/testsuite/gdb.base/local-env.exp
> +++ b/gdb/testsuite/gdb.base/local-env.exp
> @@ -59,12 +59,26 @@ gdb_test "show local-environment EDITOR" \
>       "confirm unset environment variable worked"
>   
>   # Verify that we can unset all environment variables.
> -gdb_test "unset local-environment" "" "unset all environment variables" \
> -    "Delete all environment variables. .y or n. $" \
> -    "y"
> +# Note that on some platforms this is not possible.
> +set can_unset_all 0
> +# Disable confirmation so we don't have to deal with the question.
> +gdb_test_multiple "with confirm off -- unset local-environment" \
> +    "unset all environment variables" {
> +	-re -wrap "Cannot clear the local environment on this host." {
> +	    # Nothing.
> +	    pass $gdb_test_name
> +	}
> +
> +	-re "\r\n$gdb_prompt $" {
> +	    set can_unset_all 1
> +	    pass $gdb_test_name
> +	}
> +    }
>   
> -gdb_test_no_output "show local-environment" \
> -    "all environment variables have been unset"
> +if {$can_unset_all} {
> +    gdb_test_no_output "show local-environment" \
> +	"all environment variables have been unset"
> +}
>   
>   # Verify that we can set a specific environment variable.
>   test_set_show_env_var "EDITOR" "emacs" "set environment variable"
> 
> base-commit: 7979dbef836b1c8035b9fe9dd6e09c342d85a5e2