[Buildroot] [RFC next 1/2] linux: fix builds for kernels < 5.6 and host-gcc >= 10

[Julien Olivain]

During a linux-backports update, it was found that kernel v3.10.108 was
failing to compile. See:
https://lists.buildroot.org/pipermail/buildroot/2022-August/649507.html

This issue was introduced by commit 9b41b54be07711c10ad13ce157be272ed1cf402e
"linux: fix build with host-gcc 10+", which removes all declarations of
"yylloc" symbols in the dtc parser. This symbol is generated by bison, if the
"%locations" directive is provided in the parser. See:
https://git.savannah.gnu.org/cgit/bison.git/tree/doc/bison.texi?h=v3.8.2#n5984

Kernel versions < 5.6 did not include this directive, so removing all
yylloc declararions in the parser also was failing for those version.

In the kernel, dtc was updated to v1.5.1-22-gc40aeb60b47a in:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cec114e36606412908a35695a5db944cec2e3db
This commit is included in kernel v5.6.

This dtc update include the dtc commit:
https://git.kernel.org/pub/scm/utils/dtc/dtc.git/commit/?id=7150286225476345bd6e7312331e3baf4d621c32
which adds the '%locations' directive.

This commit fixes the issue by programmatically adding the '%locations'
Bison directive, if it's not found in the parser file.

Fixes:
- https://bugs.busybox.net/show_bug.cgi?id=14971

Signed-off-by: Julien Olivain <ju.o at free.fr>
---
Tested by:
- Building a recent kernel:
  qemu_aarch64_virt_defconfig (Kernel v5.15.18)
- Building an old kernel:
  qemu_arm_vexpress_defconfig with kernel 3.10.108
---
 linux/linux.mk | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/linux/linux.mk b/linux/linux.mk
index 3d9ac37959..f3eb9c32cb 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -155,6 +155,7 @@ LINUX_MAKE_FLAGS = \
 	INSTALL_MOD_PATH=$(TARGET_DIR) \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
 	WERROR=0 \
+	REGENERATE_PARSERS=1 \
 	DEPMOD=$(HOST_DIR)/sbin/depmod
 
 ifeq ($(BR2_REPRODUCIBLE),y)
@@ -286,6 +287,19 @@ define LINUX_DROP_YYLLOC
 endef
 LINUX_POST_PATCH_HOOKS += LINUX_DROP_YYLLOC
 
+# Kernel version < 5.6 breaks if host-gcc version is >= 10 and
+# 'yylloc' symbol is removed in previous hook, due to missing
+# '%locations' bison directive in dtc-parser.y.  See:
+# https://bugs.busybox.net/show_bug.cgi?id=14971
+define LINUX_ADD_DTC_LOCATIONS
+	$(Q)DTC_PARSER=$(@D)/scripts/dtc/dtc-parser.y; \
+	if test -e "$${DTC_PARSER}" \
+		&& ! grep -Eq '^%locations$$' "$${DTC_PARSER}" ; then \
+		$(SED) '/^%{$$/i %locations' "$${DTC_PARSER}"; \
+	fi
+endef
+LINUX_POST_PATCH_HOOKS += LINUX_ADD_DTC_LOCATIONS
+
 # Older linux kernels use deprecated perl constructs in timeconst.pl
 # that were removed for perl 5.22+ so it breaks on newer distributions
 # Try a dry-run patch to see if this applies, if it does go ahead
-- 
2.37.2