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

Tom de Vries
2025-12-11T08:40:59Z

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