boot/syslinux: fix install with top-level parallel build

syslinux is... special. It is a target package, but it is installed in
HOST_DIR *in the target install commands*: in addition to the boot files
that run on the target, syslinux installs a set of host tools that are
to be used at build time (e.g. extlinux, to prepare bootable media, like
an iso96660 image). Then, from HOST_DIR, the actual boot files are
copied into BINARIES_DIR (i.e. images/); we do it that way because the
boot files are scattered about everywhere in the build tree, while they
are all packed together in a single directory once installed.

However, there is no dependency between the target and image install
steps. So, when using top-level parallel builds, there is no guarantee
that the target install commands are finished before the image install
commands are started.

We fix that by first installing into a temporary location, as part of
the build step, and by then copying from there as part of the install
step. This ensures that the boot files are easily available, without
needing a dependency on the target install step, that we can't express.

Note that we do not change the actual installation into HOST_DIR: it can
be set up differently that our temporary location, and we do not want
to duplicate that setup here (it's going to diverge over time).

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 90e76818a135417d97869b6292cf0590452c3686)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

boot/syslinux/syslinux.mk

@@ -56,6 +56,11 @@ SYSLINUX_POST_PATCH_HOOKS += SYSLINUX_CLEANUP
 # syslinux build system has no convenient way to pass CFLAGS,
 # and the internal zlib should take precedence so -I shouldn't
 # be used.
+# Install in a temporary location that eases final install into
+# images/ (see corresponding command, below).
+# Repeat the target, otherwise syslinux will try to build everything
+# Repeat LD (and CC) as it happens that some binaries are linked at
+# install-time.
 define SYSLINUX_BUILD_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE1) \
 		ASCIIDOC_OK=-1 \
@@ -70,6 +75,10 @@ define SYSLINUX_BUILD_CMDS
 		LDFLAGS_FOR_BUILD="$(HOST_LDFLAGS)" \
 		PYTHON=$(HOST_DIR)/bin/python3 \
 		$(SYSLINUX_EFI_ARGS) -C $(@D) $(SYSLINUX_TARGET)
+	$(TARGET_MAKE_ENV) $(MAKE1) $(SYSLINUX_EFI_ARGS) INSTALLROOT=$(@D)/br-root.temp \
+		CC="$(TARGET_CC)" \
+		LD="$(TARGET_LD)" \
+		-C $(@D) $(SYSLINUX_TARGET) install
 endef
 
 # While the actual bootloader is compiled for the target, several
@@ -77,6 +86,8 @@ endef
 # Repeat the target, otherwise syslinux will try to build everything
 # Repeat LD (and CC) as it happens that some binaries are linked at
 # install-time.
+# Don't use the temporarily-installed br-root.temp: HOST_DIR may be setup
+# differently (merged usr, merged bin...)
 define SYSLINUX_INSTALL_TARGET_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE1) $(SYSLINUX_EFI_ARGS) INSTALLROOT=$(HOST_DIR) \
 		CC="$(TARGET_CC)" \
@@ -99,15 +110,15 @@ SYSLINUX_IMAGES-$(BR2_TARGET_SYSLINUX_EFI) += $(SYSLINUX_EFI_BITS)/efi/syslinux.
 
 SYSLINUX_C32 = $(call qstrip,$(BR2_TARGET_SYSLINUX_C32))
 
-# We install the c32 modules from the host-installed tree, where they
-# are all neatly installed in a single location, while they are
+# We install the c32 modules from the temporarily installed tree, where
+# they are all neatly installed in a single location, while they are
 # scattered around everywhere in the build tree.
 define SYSLINUX_INSTALL_IMAGES_CMDS
 	for i in $(SYSLINUX_IMAGES-y); do \
 		$(INSTALL) -D -m 0755 $(@D)/$$i $(BINARIES_DIR)/syslinux/$${i##*/}; \
 	done
 	for i in $(SYSLINUX_C32); do \
-		$(INSTALL) -D -m 0755 $(HOST_DIR)/share/syslinux/$${i} \
+		$(INSTALL) -D -m 0755 $(@D)/br-root.temp/usr/share/syslinux/$${i} \
 			$(BINARIES_DIR)/syslinux/$${i}; \
 	done
 endef