[Buildroot] [PATCHv2] toolchain/external: allow custom toolchains to use newer headers

* [Buildroot] [PATCHv2] toolchain/external: allow custom toolchains to use newer headers
@ 2020-01-06 20:10 Yann E. MORIN
  2020-01-06 20:41 ` Yann E. MORIN
  0 siblings, 1 reply; 3+ messages in thread
From: Yann E. MORIN @ 2020-01-06 20:10 UTC (permalink / raw)
  To: buildroot

From: Vincent Fazio <vfazio@xes-inc.com>

When Buildroot is released, it knows up to a certain kernel header
version, and no later. However, it is possible that an external
toolchain will be used, that uses headers newer than the latest
version Buildroot knows about.

This may also happen when testing a development, rc-class kernel
version.

In the current state, Buildroot would refuse to use such toolchains,
because the test is for strict equality.

We'd like to make that situation possible, but we also want the user
not to be lenient at the same time, and select the right headers
version when it is known.

So, we add a new Kconfig blind option that the latest kernel headers
version selects. This options is then used to decide whether we do a
strict or loose check of the kernel headers.

Suggested-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>
[yann.morin.1998 at free.fr: only do a loose check for the latest version]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

---
Changes v1 -> v2:  (Yann)
  - make it loose only for the latest version
---
 package/linux-headers/linux-headers.mk        |  3 +-
 support/scripts/check-kernel-headers.sh       | 31 ++++++++++++++++---
 toolchain/helpers.mk                          |  3 +-
 .../pkg-toolchain-external.mk                 |  3 +-
 .../Config.in.options                         | 15 +++++++++
 5 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/package/linux-headers/linux-headers.mk b/package/linux-headers/linux-headers.mk
index 676c8c44ea..ee1a6c27d7 100644
--- a/package/linux-headers/linux-headers.mk
+++ b/package/linux-headers/linux-headers.mk
@@ -135,7 +135,8 @@ define LINUX_HEADERS_CHECK_VERSION
 	$(call check_kernel_headers_version,\
 		$(BUILD_DIR),\
 		$(STAGING_DIR),\
-		$(call qstrip,$(BR2_TOOLCHAIN_HEADERS_AT_LEAST)))
+		$(call qstrip,$(BR2_TOOLCHAIN_HEADERS_AT_LEAST)),
+		strict)
 endef
 LINUX_HEADERS_POST_INSTALL_STAGING_HOOKS += LINUX_HEADERS_CHECK_VERSION
 endif
diff --git a/support/scripts/check-kernel-headers.sh b/support/scripts/check-kernel-headers.sh
index 9d23c00feb..aafa7785c1 100755
--- a/support/scripts/check-kernel-headers.sh
+++ b/support/scripts/check-kernel-headers.sh
@@ -1,9 +1,29 @@
 #!/bin/sh
 
+# This script (and the embedded C code) will check that the actual
+# headers version match the user told us they were:
+#
+# - if both versions are the same, all is well.
+#
+# - if the actual headers are older than the user told us, this is
+#   an error.
+#
+# - if the actual headers are more recent than the user told us, and
+#   we are doing a strict check, then this is an error.
+#
+# - if the actual headers are more recent than the user told us, and
+#   we are doing a loose check, then a warning is printed, but this is
+#   not an error.
+#
+# That last conditions allows a user to provide a pre-built external
+# toolchain that uses kernel headers more recent than what Buildroot
+# knew when it was released.
+
 BUILDDIR="${1}"
 SYSROOT="${2}"
 # Make sure we have enough version components
 HDR_VER="${3}.0.0"
+CHECK="${4}"  # 'strict' or 'loose'
 
 HDR_M="${HDR_VER%%.*}"
 HDR_V="${HDR_VER#*.}"
@@ -32,16 +52,19 @@ ${HOSTCC} -imacros "${SYSROOT}/usr/include/linux/version.h" \
 int main(int argc __attribute__((unused)),
          char** argv __attribute__((unused)))
 {
-    if((LINUX_VERSION_CODE & ~0xFF)
-        != KERNEL_VERSION(${HDR_M},${HDR_m},0))
+    int ret = 0;
+    int l = LINUX_VERSION_CODE & ~0xFF;
+    int h = KERNEL_VERSION(${HDR_M},${HDR_m},0);
+
+    if(l != h)
     {
         printf("Incorrect selection of kernel headers: ");
         printf("expected %d.%d.x, got %d.%d.x\n", ${HDR_M}, ${HDR_m},
                ((LINUX_VERSION_CODE>>16) & 0xFF),
                ((LINUX_VERSION_CODE>>8) & 0xFF));
-        return 1;
+        ret = ((l >= h ) && ("${CHECK}"[0] == 'l')) ? 0 : 1;
     }
-    return 0;
+    return ret;
 }
 _EOF_
 
diff --git a/toolchain/helpers.mk b/toolchain/helpers.mk
index 996cc70d44..9a1f0495a5 100644
--- a/toolchain/helpers.mk
+++ b/toolchain/helpers.mk
@@ -161,9 +161,10 @@ copy_toolchain_sysroot = \
 # $1: build directory
 # $2: sysroot directory
 # $3: kernel version string, in the form: X.Y
+# $4: test to do, 'strict' or 'loose'
 #
 check_kernel_headers_version = \
-	if ! support/scripts/check-kernel-headers.sh $(1) $(2) $(3); then \
+	if ! support/scripts/check-kernel-headers.sh $(1) $(2) $(3) $(4); then \
 		exit 1; \
 	fi
 
diff --git a/toolchain/toolchain-external/pkg-toolchain-external.mk b/toolchain/toolchain-external/pkg-toolchain-external.mk
index 1c43409514..0f1a7a5cd3 100644
--- a/toolchain/toolchain-external/pkg-toolchain-external.mk
+++ b/toolchain/toolchain-external/pkg-toolchain-external.mk
@@ -542,7 +542,8 @@ define $(2)_CONFIGURE_CMDS
 	$$(call check_kernel_headers_version,\
 		$$(BUILD_DIR)\
 		$$(call toolchain_find_sysroot,$$(TOOLCHAIN_EXTERNAL_CC)),\
-		$$(call qstrip,$$(BR2_TOOLCHAIN_HEADERS_AT_LEAST))); \
+		$$(call qstrip,$$(BR2_TOOLCHAIN_HEADERS_AT_LEAST)),
+		$(if $(BR2_TOOLCHAIN_EXTERNAL_HEADERS_LATEST),loose,strict)); \
 	$$(call check_gcc_version,$$(TOOLCHAIN_EXTERNAL_CC),\
 		$$(call qstrip,$$(BR2_TOOLCHAIN_GCC_AT_LEAST))); \
 	if test "$$(BR2_arm)" = "y" ; then \
diff --git a/toolchain/toolchain-external/toolchain-external-custom/Config.in.options b/toolchain/toolchain-external/toolchain-external-custom/Config.in.options
index 665765a104..ed0a1b4421 100644
--- a/toolchain/toolchain-external/toolchain-external-custom/Config.in.options
+++ b/toolchain/toolchain-external/toolchain-external-custom/Config.in.options
@@ -92,6 +92,13 @@ config BR2_TOOLCHAIN_EXTERNAL_GCC_OLD
 
 endchoice
 
+# This should be selected by a single version, below, to indicate that
+# Buildroot does not know of mor erecent headers than the ones selected.
+# This allows using toolchains with headers more recent than Buildroot
+# knows about, while still enforcing strict check for older headers.
+config BR2_TOOLCHAIN_EXTERNAL_HEADERS_LATEST
+	bool
+
 choice
 	bool "External toolchain kernel headers series"
 	default BR2_TOOLCHAIN_EXTERNAL_HEADERS_REALLY_OLD
@@ -109,9 +116,17 @@ choice
 	    m = ( LINUX_VERSION_CODE >> 8  ) & 0xFF
 	    p = ( LINUX_VERSION_CODE >> 0  ) & 0xFF
 
+	  If your toolchain uses headers newer than the latest version
+	  in the choice, then select the latest version.
+
+# Note: when adding a new version here, be sure to move the
+# 'select BR2_TOOLCHAIN_EXTERNAL_HEADERS_LATEST' from the
+# current "latest version" to that new "latest version".
+
 config BR2_TOOLCHAIN_EXTERNAL_HEADERS_5_4
 	bool "5.4.x"
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_4
+	select BR2_TOOLCHAIN_EXTERNAL_HEADERS_LATEST
 
 config BR2_TOOLCHAIN_EXTERNAL_HEADERS_5_3
 	bool "5.3.x"
-- 
2.20.1

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