Don't compile programs using fork() on MMU-less systems

Systems that lack a MMU cannot use fork() to create the child process.
The patch does not compile the affected programs on MMU-less systems.

Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

CMakeLists.txt

@@ -2,6 +2,7 @@ cmake_minimum_required(VERSION 3.3)
 
 project(can-utils LANGUAGES C)
 
+include (CheckFunctionExists)
 include (CheckSymbolExists)
 include (GNUInstallDirs)
 
@@ -25,12 +26,13 @@ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DSCM_TXTIME=SO_TXTIME")
 include_directories (.)
 include_directories (./include)
 
+check_function_exists(fork HAVE_FORK)
+
 set(PROGRAMS_CANLIB
     asc2log
     canbusload
     candump
     cangen
-    canlogserver
     canplayer
     cansend
     cansequence
@@ -39,6 +41,10 @@ set(PROGRAMS_CANLIB
     slcanpty
 )
 
+if(HAVE_FORK)
+    list(APPEND PROGRAMS_CANLIB canlogserver)
+endif()
+
 set(PROGRAMS_J1939
     j1939acd
     j1939cat
@@ -49,7 +55,6 @@ set(PROGRAMS_J1939
 
 set(PROGRAMS
     ${PROGRAMS_CANLIB}
-    bcmserver
     canfdtest
     cangw
     cansniffer
@@ -57,13 +62,17 @@ set(PROGRAMS
     isotpperf
     isotprecv
     isotpsend
-    isotpserver
     isotpsniffer
     isotptun
     slcan_attach
     slcand
 )
 
+if(HAVE_FORK)
+    list(APPEND PROGRAMS bcmserver)
+    list(APPEND PROGRAMS isotpserver)
+endif()
+
 add_executable(can-calc-bit-timing
     calc-bit-timing/can-calc-bit-timing.c
 )

GNUmakefile.am

@@ -75,14 +75,12 @@ EXTRA_DIST += \
 
 bin_PROGRAMS = \
 	asc2log \
-	bcmserver \
 	can-calc-bit-timing \
 	canbusload \
 	candump \
 	canfdtest \
 	cangen \
 	cangw \
-	canlogserver \
 	canplayer \
 	cansend \
 	cansequence \
@@ -91,7 +89,6 @@ bin_PROGRAMS = \
 	isotpperf \
 	isotprecv \
 	isotpsend \
-	isotpserver \
 	isotpsniffer \
 	isotptun \
 	j1939acd \
@@ -106,6 +103,13 @@ bin_PROGRAMS = \
 	slcanpty \
 	testj1939
 
+if HAVE_FORK
+bin_PROGRAMS += \
+	bcmserver \
+	canlogserver \
+	isotpserver
+endif
+
 j1939acd_LDADD = libj1939.la
 j1939cat_LDADD = libj1939.la
 j1939spy_LDADD = libj1939.la

Makefile

@@ -45,6 +45,8 @@ MAKEFLAGS := -k
 
 CFLAGS := -O2 -Wall -Wno-parentheses
 
+HAVE_FORK := $(shell ./check_cc.sh "$(CC)" fork_test.c)
+
 CPPFLAGS += \
 	-I. \
 	-Iinclude \
@@ -66,10 +68,14 @@ PROGRAMS_ISOTP := \
 	isotpperf \
 	isotprecv \
 	isotpsend \
-	isotpserver \
 	isotpsniffer \
 	isotptun
 
+ifeq ($(HAVE_FORK),1)
+PROGRAMS_ISOTP += \
+	isotpserver
+endif
+
 PROGRAMS_J1939 := \
 	j1939acd \
 	j1939cat \
@@ -87,14 +93,12 @@ PROGRAMS := \
 	$(PROGRAMS_J1939) \
 	$(PROGRAMS_SLCAN) \
 	asc2log \
-	bcmserver \
 	can-calc-bit-timing \
 	canbusload \
 	candump \
 	canfdtest \
 	cangen \
 	cansequence \
-	canlogserver \
 	canplayer \
 	cansend \
 	cansniffer \
@@ -103,6 +107,12 @@ PROGRAMS := \
 	mcp251xfd-dump \
 	slcanpty
 
+ifeq ($(HAVE_FORK),1)
+PROGRAMS += \
+	canlogserver \
+	bcmserver
+endif
+
 all: $(PROGRAMS)
 
 clean:

check_cc.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+# check_cc.sh - Helper to test userspace compilation support
+# Copyright (c) 2015 Andrew Lutomirski
+
+CC="$1"
+TESTPROG="$2"
+shift 2
+
+if [ -n "$CC" ] && $CC -o /dev/null "$TESTPROG" -O0 "$@"; then
+    echo 1
+else
+    echo 0
+fi
+
+exit 0

configure.ac

@@ -76,6 +76,8 @@ AC_CHECK_FUNCS([ \
 	strtoul \
 ])
 
+AM_CONDITIONAL(HAVE_FORK, test "$ac_cv_func_fork_works" = "yes")
+
 # glibc versions before 2.17 needs to link with -lrt for clock_nanosleep
 AC_SEARCH_LIBS([clock_nanosleep], [rt])
 

fork_test.c

@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 Dario Binacchi <dario.binacchi@amarulasolutions.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the version 2 of the GNU General Public License
+ * as published by the Free Software Foundation
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+	fork();
+
+	return 0;
+}