build: automatically generate header dependencies

Instead of manually specifying which source files depend on which
headers, use compiler flags to automatically generate depfiles (.d),
which declare the correct header (make) dependencies for each source
file (.c).

Use `-MMD` (which ignores system headers) to generate the dependencies
and `-MP` to prevent make from complaining when a header file is removed
while it is listed as a dependency in a depfile.

If depfiles exist, just include them.  If not, make each object file
(.o) unconditionally depend on all header files in its source directory
and in src/include, to ensure that rebuilds are done when needed.  The
latter case applies to the first build after `make clean` (which would
build everything anyway) and when the compiler does not support
generating depfiles.

Note that both gcc and clang have supported these options for a long
time.

Misc: This depends on the changes from commit 5b1bd33c7 ("build: use
full paths on compile/link targets", 2023-07-02) / PR #6158 to avoid
issues with make dependency tracking.

24 files changed, 77 insertions, 52 deletions

diff --git a/.gitignore b/.gitignore
index fd35dde40..3413abd55 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+*.d
 *.o
 *.so
 *~
diff --git a/config.mk.in b/config.mk.in
index 63d7fb981..1521a2633 100644
--- a/config.mk.in
+++ b/config.mk.in
@@ -81,6 +81,7 @@ LDFLAGS=@LDFLAGS@
 
 # Project variables
 EXTRA_CFLAGS  =@EXTRA_CFLAGS@
+DEPS_CFLAGS   =@DEPS_CFLAGS@
 COMMON_CFLAGS = \
         -ggdb -O2 -DVERSION='"$(VERSION)"' \
         -Wall -Wextra $(HAVE_FATAL_WARNINGS) \
@@ -88,16 +89,18 @@ COMMON_CFLAGS = \
         -fstack-protector-all -D_FORTIFY_SOURCE=2 \
         -DPREFIX='"$(prefix)"' -DSYSCONFDIR='"$(sysconfdir)/firejail"' \
         -DLIBDIR='"$(libdir)"' -DBINDIR='"$(bindir)"' \
-        -DVARDIR='"/var/lib/firejail"' \
+        -DVARDIR='"/var/lib/firejail"'
 
 PROG_CFLAGS = \
         $(COMMON_CFLAGS) \
         $(HAVE_GCOV) $(MANFLAGS) \
         $(EXTRA_CFLAGS) \
+        $(DEPS_CFLAGS) \
         -fPIE
 
 SO_CFLAGS = \
         $(COMMON_CFLAGS) \
+        $(DEPS_CFLAGS) \
         -fPIC
 
 EXTRA_LDFLAGS =@EXTRA_LDFLAGS@
@@ -105,4 +108,4 @@ PROG_LDFLAGS  = -Wl,-z,relro -Wl,-z,now -fPIE -pie $(EXTRA_LDFLAGS)
 SO_LDFLAGS    = -Wl,-z,relro -Wl,-z,now -fPIC
 LIBS =@LIBS@
 
-CLEANFILES = *.o *.gcov *.gcda *.gcno *.plist
+CLEANFILES = *.d *.o *.gcov *.gcda *.gcno *.plist
diff --git a/configure b/configure
index 767d1da00..adcd6162b 100755
--- a/configure
+++ b/configure
@@ -682,6 +682,7 @@ PKG_CONFIG_PATH
 PKG_CONFIG
 HAVE_APPARMOR
 HAVE_IDS
+DEPS_CFLAGS
 OBJEXT
 EXEEXT
 ac_ct_CC
@@ -3270,8 +3271,51 @@ ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
-HAVE_SPECTRE="no"
+DEPS_CFLAGS=""
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -MMD -MP" >&5
+printf %s "checking whether C compiler accepts -MMD -MP... " >&6; }
+if test ${ax_cv_check_cflags___MMD__MP+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS  -MMD -MP"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main (void)
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"
+then :
+  ax_cv_check_cflags___MMD__MP=yes
+else $as_nop
+  ax_cv_check_cflags___MMD__MP=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags___MMD__MP" >&5
+printf "%s\n" "$ax_cv_check_cflags___MMD__MP" >&6; }
+if test "x$ax_cv_check_cflags___MMD__MP" = xyes
+then :
+
+        DEPS_CFLAGS="$DEPS_CFLAGS -MMD -MP"
+
+else $as_nop
+  :
+fi
 
+
+HAVE_SPECTRE="no"
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -mindirect-branch=thunk" >&5
 printf %s "checking whether C compiler accepts -mindirect-branch=thunk... " >&6; }
 if test ${ax_cv_check_cflags___mindirect_branch_thunk+y}
@@ -5311,6 +5355,7 @@ Compile options:
    CPPFLAGS: $CPPFLAGS
    LDFLAGS: $LDFLAGS
    EXTRA_CFLAGS: $EXTRA_CFLAGS
+   DEPS_CFLAGS: $DEPS_CFLAGS
    EXTRA_LDFLAGS: $EXTRA_LDFLAGS
    LIBS: $LIBS
    fatal warnings: $HAVE_FATAL_WARNINGS
diff --git a/configure.ac b/configure.ac
index d3b05d839..7a2c379fe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -20,6 +20,12 @@ AC_CONFIG_MACRO_DIR([m4])
 
 AC_PROG_CC
 
+DEPS_CFLAGS=""
+AC_SUBST([DEPS_CFLAGS])
+AX_CHECK_COMPILE_FLAG([-MMD -MP], [
+        DEPS_CFLAGS="$DEPS_CFLAGS -MMD -MP"
+])
+
 HAVE_SPECTRE="no"
 AX_CHECK_COMPILE_FLAG([-mindirect-branch=thunk], [
         HAVE_SPECTRE="yes"
@@ -279,6 +285,7 @@ Compile options:
    CPPFLAGS: $CPPFLAGS
    LDFLAGS: $LDFLAGS
    EXTRA_CFLAGS: $EXTRA_CFLAGS
+   DEPS_CFLAGS: $DEPS_CFLAGS
    EXTRA_LDFLAGS: $EXTRA_LDFLAGS
    LIBS: $LIBS
    fatal warnings: $HAVE_FATAL_WARNINGS
diff --git a/src/etc-cleanup/Makefile b/src/etc-cleanup/Makefile
index 23121c521..d9dcdbea8 100644
--- a/src/etc-cleanup/Makefile
+++ b/src/etc-cleanup/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/etc_groups.h
-
 include $(ROOT)/src/prog.mk
diff --git a/src/fbuilder/Makefile b/src/fbuilder/Makefile
index f0e374a52..70c5fb008 100644
--- a/src/fbuilder/Makefile
+++ b/src/fbuilder/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/syscall.h
-
 include $(ROOT)/src/prog.mk
diff --git a/src/fcopy/Makefile b/src/fcopy/Makefile
index a9f706eb8..4897980e7 100644
--- a/src/fcopy/Makefile
+++ b/src/fcopy/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/syscall.h
 EXTRA_OBJS = ../lib/common.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fids/Makefile b/src/fids/Makefile
index 7bdbe0590..dadb17a1b 100644
--- a/src/fids/Makefile
+++ b/src/fids/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h
-
 include $(ROOT)/src/prog.mk
diff --git a/src/firecfg/Makefile b/src/firecfg/Makefile
index cc7a27c52..6cbd1b5ba 100644
--- a/src/firecfg/Makefile
+++ b/src/firecfg/Makefile
@@ -7,13 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = \
-../include/common.h \
-../include/euid_common.h \
-../include/libnetlink.h \
-../include/firejail_user.h \
-../include/pid.h
-
 EXTRA_OBJS = ../lib/common.o ../lib/firejail_user.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/firejail/Makefile b/src/firejail/Makefile
index 1c4b1b5c2..e7b334cd8 100644
--- a/src/firejail/Makefile
+++ b/src/firejail/Makefile
@@ -7,19 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = \
-../include/rundefs.h \
-../include/common.h \
-../include/ldd_utils.h \
-../include/euid_common.h \
-../include/pid.h \
-../include/seccomp.h \
-../include/syscall_i386.h \
-../include/syscall_x86_64.h \
-../include/firejail_user.h \
-../include/etc_groups.h
-
-
 EXTRA_OBJS = \
 ../lib/common.o \
 ../lib/ldd_utils.o \
diff --git a/src/firemon/Makefile b/src/firemon/Makefile
index 0e39f8b01..02e3b6eed 100644
--- a/src/firemon/Makefile
+++ b/src/firemon/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/pid.h
 EXTRA_OBJS = ../lib/common.o ../lib/pid.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fldd/Makefile b/src/fldd/Makefile
index 246cbc183..3e48b43ab 100644
--- a/src/fldd/Makefile
+++ b/src/fldd/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/syscall.h ../include/ldd_utils.h
 EXTRA_OBJS = ../lib/common.o ../lib/ldd_utils.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fnet/Makefile b/src/fnet/Makefile
index c98326dc4..dfeefdc47 100644
--- a/src/fnet/Makefile
+++ b/src/fnet/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/libnetlink.h
 EXTRA_OBJS = ../lib/common.o ../lib/libnetlink.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fnetfilter/Makefile b/src/fnetfilter/Makefile
index c8992c3d6..778de3a8b 100644
--- a/src/fnetfilter/Makefile
+++ b/src/fnetfilter/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/syscall.h
 EXTRA_OBJS = ../lib/common.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fsec-optimize/Makefile b/src/fsec-optimize/Makefile
index caead9d54..babed1fdb 100644
--- a/src/fsec-optimize/Makefile
+++ b/src/fsec-optimize/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/seccomp.h ../include/syscall.h
 EXTRA_OBJS = ../lib/common.o ../lib/errno.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fsec-print/Makefile b/src/fsec-print/Makefile
index 43cc42fed..bf383d2d0 100644
--- a/src/fsec-print/Makefile
+++ b/src/fsec-print/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/seccomp.h ../include/syscall.h
 EXTRA_OBJS = ../lib/common.o ../lib/errno.o ../lib/syscall.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fseccomp/Makefile b/src/fseccomp/Makefile
index 89b12f629..66bb58444 100644
--- a/src/fseccomp/Makefile
+++ b/src/fseccomp/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/syscall.h
 EXTRA_OBJS = ../lib/common.o ../lib/errno.o ../lib/syscall.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/fzenity/Makefile b/src/fzenity/Makefile
index 3c1aa0574..4cebe7ac5 100644
--- a/src/fzenity/Makefile
+++ b/src/fzenity/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h
-
 include $(ROOT)/src/prog.mk
diff --git a/src/jailcheck/Makefile b/src/jailcheck/Makefile
index 1823ee9d0..431a21c8e 100644
--- a/src/jailcheck/Makefile
+++ b/src/jailcheck/Makefile
@@ -7,7 +7,6 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h ../include/pid.h
 EXTRA_OBJS = ../lib/common.o ../lib/pid.o
 
 include $(ROOT)/src/prog.mk
diff --git a/src/libpostexecseccomp/Makefile b/src/libpostexecseccomp/Makefile
index f66fdd0d7..a8d3fd8b7 100644
--- a/src/libpostexecseccomp/Makefile
+++ b/src/libpostexecseccomp/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 SO = $(MOD_DIR)/$(MOD).so
 TARGET = $(SO)
 
-EXTRA_HDRS = ../include/seccomp.h ../include/rundefs.h
-
 include $(ROOT)/src/so.mk
diff --git a/src/libtracelog/Makefile b/src/libtracelog/Makefile
index a83726167..e9330236c 100644
--- a/src/libtracelog/Makefile
+++ b/src/libtracelog/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 SO = $(MOD_DIR)/$(MOD).so
 TARGET = $(SO)
 
-EXTRA_HDRS = ../include/rundefs.h
-
 include $(ROOT)/src/so.mk
diff --git a/src/profstats/Makefile b/src/profstats/Makefile
index 8f33ce1de..213b1476d 100644
--- a/src/profstats/Makefile
+++ b/src/profstats/Makefile
@@ -7,6 +7,4 @@ MOD_DIR = $(ROOT)/src/$(MOD)
 PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
-EXTRA_HDRS = ../include/common.h
-
 include $(ROOT)/src/prog.mk
diff --git a/src/prog.mk b/src/prog.mk
index debdf3572..a639e87fc 100644
--- a/src/prog.mk
+++ b/src/prog.mk
@@ -3,16 +3,22 @@
 # Note: $(ROOT)/config.mk must be included before this file.
 #
 # The includer should probably define PROG and TARGET and may also want to
-# define EXTRA_HDRS and EXTRA_OBJS and extend CLEANFILES.
+# define EXTRA_OBJS and extend CLEANFILES.
 
-HDRS := $(sort $(wildcard $(MOD_DIR)/*.h))
+HDRS :=
 SRCS := $(sort $(wildcard $(MOD_DIR)/*.c))
 OBJS := $(SRCS:.c=.o)
+DEPS := $(sort $(wildcard $(OBJS:.o=.d)))
+
+ifeq ($(DEPS),)
+HDRS := $(sort $(wildcard $(MOD_DIR)/*.h $(ROOT)/src/include/*.h))
+endif
 
 .PHONY: all
 all: $(TARGET)
+-include $(DEPS)
 
-%.o : %.c $(HDRS) $(EXTRA_HDRS) $(ROOT)/config.mk
+%.o : %.c $(HDRS) $(ROOT)/config.mk
         $(CC) $(PROG_CFLAGS) $(CFLAGS) $(CPPFLAGS) -c $< -o $@
 
 $(PROG): $(OBJS) $(EXTRA_OBJS) $(ROOT)/config.mk
diff --git a/src/so.mk b/src/so.mk
index 95b524081..ac76ffc30 100644
--- a/src/so.mk
+++ b/src/so.mk
@@ -3,16 +3,22 @@
 # Note: $(ROOT)/config.mk must be included before this file.
 #
 # The includer should probably define SO and TARGET and may also want to define
-# EXTRA_HDRS and EXTRA_OBJS and extend CLEANFILES.
+# EXTRA_OBJS and extend CLEANFILES.
 
-HDRS := $(sort $(wildcard $(MOD_DIR)/*.h))
+HDRS :=
 SRCS := $(sort $(wildcard $(MOD_DIR)/*.c))
 OBJS := $(SRCS:.c=.o)
+DEPS := $(sort $(wildcard $(OBJS:.o=.d)))
+
+ifeq ($(DEPS),)
+HDRS := $(sort $(wildcard $(MOD_DIR)/*.h $(ROOT)/src/include/*.h))
+endif
 
 .PHONY: all
 all: $(TARGET)
+-include $(DEPS)
 
-%.o : %.c $(HDRS) $(EXTRA_HDRS) $(ROOT)/config.mk
+%.o : %.c $(HDRS) $(ROOT)/config.mk
         $(CC) $(SO_CFLAGS) $(CFLAGS) $(CPPFLAGS) -c $< -o $@
 
 $(SO): $(OBJS) $(EXTRA_OBJS) $(ROOT)/config.mk