[PATCH] make debug symbols of kernel build relocatable

[PATCH] make debug symbols of kernel build relocatable

[Felix Moessbauer]

This patch adds support to inject custom KCFLAGS into
the linux-custom kernel build.
Using this infrastructure, we add the debug-prefix-map
flag to strip off the absolute prefix of the sources location.
This makes the debug information relocatable.

By that, we also fix low ccache hit rates in combination with ssbuild
due to the random builddir that sbuild uses.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 meta/recipes-kernel/linux/files/debian/isar/build.tmpl | 2 +-
 meta/recipes-kernel/linux/files/debian/rules.tmpl      | 3 ++-
 meta/recipes-kernel/linux/linux-custom.inc             | 4 ++++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
index b7749cec..8fe816b3 100644
--- a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
@@ -22,7 +22,7 @@ do_build() {
     set -x
 
     # Build the Linux kernel
-    ${MAKE} O=${KERNEL_BUILD_DIR} ${PARALLEL_MAKE} || exit ${?}
+    ${MAKE} O=${KERNEL_BUILD_DIR} ${PARALLEL_MAKE} KCFLAGS="${KCFLAGS}" || exit ${?}
 
     # Stop tracing
     set +x
diff --git a/meta/recipes-kernel/linux/files/debian/rules.tmpl b/meta/recipes-kernel/linux/files/debian/rules.tmpl
index a1166287..8063c495 100755
--- a/meta/recipes-kernel/linux/files/debian/rules.tmpl
+++ b/meta/recipes-kernel/linux/files/debian/rules.tmpl
@@ -13,7 +13,8 @@ isar_env=$(strip \
 	export DEB_HOST_GNU_TYPE='$(DEB_HOST_GNU_TYPE)' && \
 	export MAKE='$(MAKE)' && \
 	export O='${O}' && \
-	export S='${S}' \
+	export S='${S}' && \
+	export CURDIR='$(CURDIR)' \
 )
 
 %:
diff --git a/meta/recipes-kernel/linux/linux-custom.inc b/meta/recipes-kernel/linux/linux-custom.inc
index a6b1cdab..55bf0418 100644
--- a/meta/recipes-kernel/linux/linux-custom.inc
+++ b/meta/recipes-kernel/linux/linux-custom.inc
@@ -78,11 +78,15 @@ TEMPLATE_VARS += "                \
     LINUX_VERSION_EXTENSION       \
     KERNEL_NAME_PROVIDED          \
     KERNEL_CONFIG_FRAGMENTS       \
+    KCFLAGS                       \
 "
 
 inherit dpkg
 inherit template
 
+# Add custom cflags to the kernel build
+KCFLAGS ?= "-fdebug-prefix-map=${CURDIR}=."
+
 # Derive name of the kernel packages from the name of this recipe
 KERNEL_NAME_PROVIDED ?= "${@ d.getVar('PN', True).partition('linux-')[2]}"
 
-- 
2.30.2

Re: [PATCH] make debug symbols of kernel build relocatable

[Uladzimir Bely]

In the email from Monday, 18 July 2022 18:50:56 +03 user Felix Moessbauer 
wrote:
> This patch adds support to inject custom KCFLAGS into
> the linux-custom kernel build.
> Using this infrastructure, we add the debug-prefix-map
> flag to strip off the absolute prefix of the sources location.
> This makes the debug information relocatable.
> 
> By that, we also fix low ccache hit rates in combination with ssbuild
> due to the random builddir that sbuild uses.

Hello.

I also came to the similar solution while debugging the issue, but I tried to 
use `-fdebug-prefix-map` directly in the build scripts.

The idea with placing it on recipe side and passing to the builder via KCFLAGS 
looks better and more extendable.

A small typo 'ssbuild' in commit message could be fixed during merge.

> 
> Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
> ---
>  meta/recipes-kernel/linux/files/debian/isar/build.tmpl | 2 +-
>  meta/recipes-kernel/linux/files/debian/rules.tmpl      | 3 ++-
>  meta/recipes-kernel/linux/linux-custom.inc             | 4 ++++
>  3 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl index
> b7749cec..8fe816b3 100644
> --- a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> +++ b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> @@ -22,7 +22,7 @@ do_build() {
>      set -x
> 
>      # Build the Linux kernel
> -    ${MAKE} O=${KERNEL_BUILD_DIR} ${PARALLEL_MAKE} || exit ${?}
> +    ${MAKE} O=${KERNEL_BUILD_DIR} ${PARALLEL_MAKE} KCFLAGS="${KCFLAGS}" ||
> exit ${?}
> 
>      # Stop tracing
>      set +x
> diff --git a/meta/recipes-kernel/linux/files/debian/rules.tmpl
> b/meta/recipes-kernel/linux/files/debian/rules.tmpl index
> a1166287..8063c495 100755
> --- a/meta/recipes-kernel/linux/files/debian/rules.tmpl
> +++ b/meta/recipes-kernel/linux/files/debian/rules.tmpl
> @@ -13,7 +13,8 @@ isar_env=$(strip \
>  	export DEB_HOST_GNU_TYPE='$(DEB_HOST_GNU_TYPE)' && \
>  	export MAKE='$(MAKE)' && \
>  	export O='${O}' && \
> -	export S='${S}' \
> +	export S='${S}' && \
> +	export CURDIR='$(CURDIR)' \
>  )
> 
>  %:
> diff --git a/meta/recipes-kernel/linux/linux-custom.inc
> b/meta/recipes-kernel/linux/linux-custom.inc index a6b1cdab..55bf0418
> 100644
> --- a/meta/recipes-kernel/linux/linux-custom.inc
> +++ b/meta/recipes-kernel/linux/linux-custom.inc
> @@ -78,11 +78,15 @@ TEMPLATE_VARS += "                \
>      LINUX_VERSION_EXTENSION       \
>      KERNEL_NAME_PROVIDED          \
>      KERNEL_CONFIG_FRAGMENTS       \
> +    KCFLAGS                       \
>  "
> 
>  inherit dpkg
>  inherit template
> 
> +# Add custom cflags to the kernel build
> +KCFLAGS ?= "-fdebug-prefix-map=${CURDIR}=."
> +
>  # Derive name of the kernel packages from the name of this recipe
>  KERNEL_NAME_PROVIDED ?= "${@ d.getVar('PN', True).partition('linux-')[2]}"


-- 
Uladzimir Bely

Re: [PATCH] make debug symbols of kernel build relocatable

[Anton Mikanovich]

18.07.2022 18:50, Felix Moessbauer wrote:
> This patch adds support to inject custom KCFLAGS into
> the linux-custom kernel build.
> Using this infrastructure, we add the debug-prefix-map
> flag to strip off the absolute prefix of the sources location.
> This makes the debug information relocatable.
>
> By that, we also fix low ccache hit rates in combination with ssbuild
> due to the random builddir that sbuild uses.
>
> Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>

Hello, can you please rebase this patch on the latest next?