Add atomvm:posix_kill/2

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added `filename:dirname/1`, `filename:basename/1,2`, `filename:extension/1`, `filename:rootname/1,2` and `filename:join/2`
 - Added `init:get_arguments/0`
+- Added `atomvm:posix_kill/2` to send a signal to a process, typically one started with `atomvm:subprocess/4`
 - Added Erlang distribution over serial (uart)
 - Added WASM32 JIT backend for Emscripten platform
 - Added `network:wifi_scan/0,1` to ESP32 network driver to scan available APs when in sta or sta+ap mode.

libs/eavmlib/src/atomvm.erl

@@ -56,7 +56,8 @@
     posix_closedir/1,
     posix_readdir/1,
     get_creation/0,
-    subprocess/4
+    subprocess/4,
+    posix_kill/2
 ]).
 
 -export_type([
@@ -518,3 +519,26 @@ get_creation() ->
     {ok, non_neg_integer(), posix_fd()} | {error, posix_error()}.
 subprocess(_Path, _Args, _Env, _Options) ->
     erlang:nif_error(undefined).
+
+%%-----------------------------------------------------------------------------
+%% @param   OsPid   operating system process id, as returned by `subprocess/4'
+%% @param   Signal  signal number to send, e.g. 15 for SIGTERM
+%% @returns `ok' or an error tuple
+%% @doc     Send a signal to a process using kill(2). Typically used to
+%%          terminate a process started with `subprocess/4'.
+%%
+%%          A return value of `ok' means kill(2) accepted the request; it does
+%%          not guarantee that the target terminated, as the signal may be
+%%          caught, blocked, or ignored. Signal `0' sends no signal and merely
+%%          performs a POSIX existence/permission check.
+%%
+%%          `OsPid' follows kill(2) semantics: a positive value targets a single
+%%          process, `0' targets the caller's process group, `-1' targets every
+%%          process the caller may signal, and a value less than `-1' targets the
+%%          process group whose id is the absolute value.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec posix_kill(OsPid :: integer(), Signal :: non_neg_integer()) ->
+    ok | {error, posix_error()}.
+posix_kill(_OsPid, _Signal) ->
+    erlang:nif_error(undefined).

src/libAtomVM/CMakeLists.txt

@@ -258,6 +258,7 @@ define_if_function_exists(libAtomVM fstat "sys/stat.h" PRIVATE HAVE_FSTAT)
 define_if_function_exists(libAtomVM unlink "unistd.h" PRIVATE HAVE_UNLINK)
 define_if_function_exists(libAtomVM rmdir "unistd.h" PRIVATE HAVE_RMDIR)
 define_if_function_exists(libAtomVM execve "unistd.h" PRIVATE HAVE_EXECVE)
+define_if_function_exists(libAtomVM kill "signal.h" PRIVATE HAVE_KILL)
 define_if_function_exists(libAtomVM tcgetattr "termios.h" PRIVATE HAVE_TCGETATTR)
 define_if_function_exists(libAtomVM closefrom "unistd.h" PRIVATE HAVE_CLOSEFROM)
 define_if_function_exists(libAtomVM getcwd "unistd.h" PUBLIC HAVE_GETCWD)

src/libAtomVM/nifs.c

@@ -1033,6 +1033,11 @@ DEFINE_MATH_NIF(tanh)
 #define IF_HAVE_OPEN_CLOSE(expr) NULL
 #define IF_HAVE_EXECVE(expr) NULL
 #endif
+#if HAVE_KILL
+#define IF_HAVE_KILL(expr) (expr)
+#else
+#define IF_HAVE_KILL(expr) NULL
+#endif
 #if HAVE_OPEN && HAVE_CLOSE && HAVE_LSEEK
 #define IF_HAVE_LSEEK(expr) (expr)
 #else

src/libAtomVM/nifs.gperf

@@ -190,6 +190,7 @@ atomvm:posix_select_read/3, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_read_nif)
 atomvm:posix_select_write/3, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_write_nif)
 atomvm:posix_select_stop/1, IF_HAVE_OPEN_CLOSE(&atomvm_posix_select_stop_nif)
 atomvm:subprocess/4, IF_HAVE_EXECVE(&atomvm_subprocess_nif)
+atomvm:posix_kill/2, IF_HAVE_KILL(&atomvm_posix_kill_nif)
 atomvm:posix_seek/3, IF_HAVE_LSEEK(&atomvm_posix_seek_nif)
 atomvm:posix_pread/3, IF_HAVE_PREAD(&atomvm_posix_pread_nif)
 atomvm:posix_pwrite/3, IF_HAVE_PWRITE(&atomvm_posix_pwrite_nif)

src/libAtomVM/posix_nifs.c

@@ -56,6 +56,11 @@
 #include <spawn.h>
 #endif
 
+#if HAVE_KILL
+#include <limits.h>
+#include <signal.h>
+#endif
+
 #include "defaultatoms.h"
 #include "erl_nif_priv.h"
 #include "globalcontext.h"
@@ -69,7 +74,7 @@
 
 term posix_errno_to_term(int err, GlobalContext *glb)
 {
-#if HAVE_OPEN && HAVE_CLOSE || defined(HAVE_CLOCK_SETTIME) || defined(HAVE_SETTIMEOFDAY)
+#if HAVE_OPEN && HAVE_CLOSE || defined(HAVE_CLOCK_SETTIME) || defined(HAVE_SETTIMEOFDAY) || HAVE_KILL
     // These are defined in SUSv1
     term result;
     switch (err) {
@@ -198,7 +203,7 @@
     return result;
 }
 
 static term errno_to_error_tuple_maybe_gc(Context *ctx)
 {
     return error_tuple_maybe_gc(errno, ctx);
 }
@@ -954,6 +959,43 @@
 #endif
 #endif
 
+#if HAVE_KILL
+static bool term_is_valid_pid(term t)
+{
+    if (!term_is_int64(t)) {
+        return false;
+    }
+    // The value must round-trip through pid_t: a larger integer would be
+    // silently truncated and target a different (possibly own) process.
+    int64_t value = term_to_int64(t);
+    return ((int64_t) (pid_t) value) == value;
+}
+
+static bool term_is_signal_number(term t)
+{
+    if (!term_is_int64(t)) {
+        return false;
+    }
+    int64_t value = term_to_int64(t);
+    return value >= 0 && value <= INT_MAX;
+}
+
+static term nif_atomvm_posix_kill(Context *ctx, int argc, term argv[])
+{
+    UNUSED(argc);
+    VALIDATE_VALUE(argv[0], term_is_valid_pid);
+    VALIDATE_VALUE(argv[1], term_is_signal_number);
+
+    pid_t pid = (pid_t) term_to_int64(argv[0]);
+    int signo = (int) term_to_int64(argv[1]);
+
+    if (UNLIKELY(kill(pid, signo) != 0)) {
+        return errno_to_error_tuple_maybe_gc(ctx);
+    }
+    return OK_ATOM;
+}
+#endif
+
 #if HAVE_MKFIFO
 static term nif_atomvm_posix_mkfifo(Context *ctx, int argc, term argv[])
 {
@@ -1836,6 +1878,12 @@
 };
 #endif
 #endif
+#if HAVE_KILL
+const struct Nif atomvm_posix_kill_nif = {
+    .base.type = NIFFunctionType,
+    .nif_ptr = nif_atomvm_posix_kill
+};
+#endif
 #if HAVE_OPEN && HAVE_CLOSE && HAVE_LSEEK
 const struct Nif atomvm_posix_seek_nif = {
     .base.type = NIFFunctionType,

src/libAtomVM/posix_nifs.h

@@ -47,6 +47,9 @@ extern const struct Nif atomvm_posix_select_stop_nif;
 extern const struct Nif atomvm_subprocess_nif;
 #endif
 #endif
+#if HAVE_KILL
+extern const struct Nif atomvm_posix_kill_nif;
+#endif
 #if HAVE_OPEN && HAVE_CLOSE && HAVE_LSEEK
 extern const struct Nif atomvm_posix_seek_nif;
 #endif

src/platforms/esp32/CMakeLists.txt

@@ -28,6 +28,8 @@ set(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")
 set(HAVE_MKFIFO "" CACHE INTERNAL "Have symbol mkfifo" FORCE)
 # Likewise with EXECVE
 set(HAVE_EXECVE "" CACHE INTERNAL "Have symbol execve" FORCE)
+# kill links to a newlib stub but there are no OS processes to signal
+set(HAVE_KILL "" CACHE INTERNAL "Have symbol kill" FORCE)
 # Force HAVE_SOCKET
 # Automatically detecting it requires to put too many components include dirs
 # in CMAKE_REQUIRED_INCLUDES as lwip includes freetos and many esp system components

src/platforms/esp32/test/CMakeLists.txt

@@ -41,6 +41,8 @@ set(HAVE_MKFIFO NO)
 set(HAVE_MKFIFO "" CACHE INTERNAL "Have symbol mkfifo" FORCE)
 set(HAVE_EXECVE NO)
 set(HAVE_EXECVE "" CACHE INTERNAL "Have symbol execve" FORCE)
+set(HAVE_KILL NO)
+set(HAVE_KILL "" CACHE INTERNAL "Have symbol kill" FORCE)
 # Force HAVE_SOCKET
 # Automatically detecting it requires to put too many components include dirs
 # in CMAKE_REQUIRED_INCLUDES as lwip includes freetos and many esp system components

src/platforms/rp2/CMakeLists.txt

@@ -54,6 +54,8 @@ set(HAVE_MKFIFO "" CACHE INTERNAL "Have symbol mkfifo" FORCE)
 set(HAVE_UNLINK "" CACHE INTERNAL "Have symbol unlink" FORCE)
 # Likewise with EXECVE
 set(HAVE_EXECVE "" CACHE INTERNAL "Have symbol execve" FORCE)
+# kill is declared in newlib's signal.h but not linkable on bare-metal
+set(HAVE_KILL "" CACHE INTERNAL "Have symbol kill" FORCE)
 # getcwd is defined in newlib header but not implemented
 set(HAVE_GETCWD "" CACHE INTERNAL "Have symbol getcwd" FORCE)
 # pread, pwrite, fsync, ftruncate, mkdir and rmdir are

src/platforms/stm32/CMakeLists.txt

@@ -103,6 +103,7 @@ endif ()
 set(HAVE_MKFIFO "" CACHE INTERNAL "Have symbol mkfifo" FORCE)
 set(HAVE_UNLINK "" CACHE INTERNAL "Have symbol unlink" FORCE)
 set(HAVE_EXECVE "" CACHE INTERNAL "Have symbol execve" FORCE)
+set(HAVE_KILL "" CACHE INTERNAL "Have symbol kill" FORCE)
 set(HAVE_OPEN "" CACHE INTERNAL "Have symbol open" FORCE)
 set(HAVE_CLOSE "" CACHE INTERNAL "Have symbol close" FORCE)
 set(HAVE_OPENDIR "" CACHE INTERNAL "Have symbol opendir" FORCE)

tests/libs/eavmlib/CMakeLists.txt

@@ -29,6 +29,7 @@ set(ERLANG_MODULES
     test_http_server
     test_mdns
     test_port
+    test_subprocess
     test_timer_manager
 )
 

tests/libs/eavmlib/test_subprocess.erl

@@ -0,0 +1,96 @@
+%
+% This file is part of AtomVM.
+%
+% Copyright 2026 Paul Guyot <pguyot@kallisys.net>
+%
+% Licensed under the Apache License, Version 2.0 (the "License");
+% you may not use this file except in compliance with the License.
+% You may obtain a copy of the License at
+%
+%    http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS,
+% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+% See the License for the specific language governing permissions and
+% limitations under the License.
+%
+% SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
+%
+
+-module(test_subprocess).
+
+-export([test/0]).
+
+test() ->
+    case erlang:system_info(machine) of
+        "ATOM" ->
+            test_atomvm();
+        _ ->
+            %% atomvm:subprocess/posix_kill are only available on AtomVM
+            ok
+    end.
+
+test_atomvm() ->
+    case atomvm:platform() of
+        generic_unix ->
+            ok = test_posix_kill(),
+            ok = test_posix_kill_badarg(),
+            ok = test_posix_kill_esrch(),
+            ok;
+        _ ->
+            %% atomvm:subprocess/posix_kill are only available on generic_unix
+            ok
+    end.
+
+%% A subprocess that would outlive the test unless killed: posix_kill
+%% terminates it, observed as EOF on its stdout pipe (the write end is
+%% closed when the process dies).
+test_posix_kill() ->
+    %% exec so the subprocess pid is sleep itself, not the wrapping shell:
+    %% killing the shell would not reliably reach sleep, which inherits the
+    %% stdout pipe and would keep read_until_eof/1 blocked.
+    {ok, OsPid, Fd} = atomvm:subprocess(
+        "/bin/sh", ["sh", "-c", "exec sleep 30"], undefined, [stdout]
+    ),
+    true = is_integer(OsPid),
+    %% SIGTERM
+    ok = atomvm:posix_kill(OsPid, 15),
+    eof = read_until_eof(Fd),
+    ok = atomvm:posix_close(Fd),
+    ok.
+
+test_posix_kill_badarg() ->
+    ok = expect_badarg(fun() -> atomvm:posix_kill(not_a_pid, 15) end),
+    ok = expect_badarg(fun() -> atomvm:posix_kill(1, not_a_signal) end),
+    %% Oversized signal must be rejected rather than truncated to a valid one.
+    ok = expect_badarg(fun() -> atomvm:posix_kill(1, 1 bsl 40) end),
+    ok.
+
+expect_badarg(Fun) ->
+    try Fun() of
+        _ -> fail
+    catch
+        error:badarg -> ok
+    end.
+
+%% Signalling a pid that cannot exist fails with esrch.
+test_posix_kill_esrch() ->
+    {error, esrch} = atomvm:posix_kill(536870911, 0),
+    ok.
+
+read_until_eof(Fd) ->
+    case atomvm:posix_read(Fd, 64) of
+        eof ->
+            eof;
+        {ok, _Data} ->
+            read_until_eof(Fd);
+        {error, eagain} ->
+            ok = atomvm:posix_select_read(Fd, self(), undefined),
+            receive
+                {select, _FdRes, undefined, ready_input} -> ok
+            after 5000 ->
+                exit(posix_kill_eof_timeout)
+            end,
+            read_until_eof(Fd)
+    end.

tests/libs/eavmlib/tests.erl

@@ -29,6 +29,7 @@ start() ->
         test_http_server,
         test_mdns,
         test_port,
+        test_subprocess,
         test_timer_manager,
         test_ahttp_client
     ]).

tests/libs/estdlib/test_serial_dist_socat.erl

@@ -223,7 +223,7 @@ test_multi_port_ping(OsPid1, SocatFd1, PtyA1, PtyB, OsPid2, SocatFd2, PtyA2, Pty
 start_socat() ->
     {ok, OsPid, Fd} = atomvm:subprocess(
         "/bin/sh",
-        ["sh", "-c", "socat -d -d pty,raw,echo=0 pty,raw,echo=0 2>&1"],
+        ["sh", "-c", "exec socat -d -d pty,raw,echo=0 pty,raw,echo=0 2>&1"],
         undefined,
         [stdout]
     ),
@@ -235,11 +235,13 @@ start_socat() ->
     {OsPid, Fd, PtyA, PtyB}.
 
 stop_socat(OsPid, Fd) ->
-    atomvm:posix_close(Fd),
-    {ok, _, KillFd} = atomvm:subprocess(
-        "/bin/kill", ["kill", integer_to_list(OsPid)], undefined, [stdout]
-    ),
-    atomvm:posix_close(KillFd).
+    %% SIGTERM; exec in start_socat makes OsPid socat itself. Tolerate esrch so
+    %% an already-exited socat does not mask the real test failure.
+    case atomvm:posix_kill(OsPid, 15) of
+        ok -> ok;
+        {error, esrch} -> ok
+    end,
+    atomvm:posix_close(Fd).
 
 start_peer(PtyPath, TestName) ->
     AvmBin = find_atomvm_binary(),