[Buildroot] [PATCH] linux: Add helping kernel gdb functions compilation

[Yann E. MORIN]

Michael, All,

On 2023-12-09 11:10 +0100, Michael Trimarchi spake thusly:
> In order to use all the features of KGDB it's nice to have
> the possibility to source the vmlinux-gdb.py file. The
> generation of this file it's a target of linux kernel.

It is automatically generated when the kernel is configured with
CONFIG_GDB_SCRIPTS, so I think the best approach would be something
along the lines of:

    package/gdb/gdb.mk:

    define HOST_GDB_LINUX_CONFIG_FIXUPS
        $(call KCONFIG_ENABLE_OPT,CONFIG_GDB_SCRIPTS)
    endef

See:
    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile#n1748
and:
    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile#n1752

Regards,
Yann E. MORIN.

> Add it
> in order to use gdb of vmlinux in output directory including
> tx-* linux script
> 
> gdb-multiarch --tui output/build/<linux dir>/vmlinux
> add-auto-load-safe-path output/build/<linux dir>
> source output/build/<linux dir>/vmlinux-gdb.py
> 
> Linux needs to be compiled with DEBUG_INFO (without restrict
> DEBUG_INFO) and kernel cmdline should be modified to wait
> of kgdb if needed. As example
> 
> kgdboc_earlycon=ns16550a kgdboc=/dev/ttyS2 kgdbwait nokaslr
> 
> The test was done on am62x board over serial line. In order
> to have it running properly we need to compile the agent-proxy
> 
> ./output/host/bin/agent-proxy 4440 4441 0 /dev/ttyUSB0 115200
> 
> gdb can now having the debugging uart available using:
> 
> target remote localhost:4441
> 
> the 4440 is used by the console and 4441 is used to debug
> 
> Tested-by: Michael Trimarchi <michael at amarulasolutions.com>
> Signed-off-by: Michael Trimarchi <michael at amarulasolutions.com>
> ---
>  linux/Config.in | 7 +++++++
>  linux/linux.mk  | 7 +++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/linux/Config.in b/linux/Config.in
> index ae734c49a0..71ab27bbcb 100644
> --- a/linux/Config.in
> +++ b/linux/Config.in
> @@ -486,6 +486,13 @@ config BR2_LINUX_KERNEL_NEEDS_HOST_PAHOLE
>  	  such as "BTF: .tmp_vmlinux.btf: pahole (pahole) is not
>  	  available".
>  
> +config BR2_LINUX_KERNEL_ADD_HOST_GDB_SCRIPTS
> +	bool "Need tools for debugging with kgdb"
> +	help
> +	  Add helping script to be used with gdb and kgdb in order to
> +	  debug linux kernel. Those convinients scripts add some feature
> +	  command to gdb with specific python script
> +
>  # Linux extensions
>  source "linux/Config.ext.in"
>  
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 1db5c6046d..e8cdb26793 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -488,6 +488,12 @@ LINUX_APPEND_DTB += ; \
>  endif
>  endif
>  
> +ifeq ($(BR2_LINUX_KERNEL_ADD_HOST_GDB_SCRIPTS),y)
> +define LINUX_BUILD_GDB_SCRIPTS
> +	$(LINUX_MAKE_ENV) $(BR2_MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) scripts_gdb
> +endef
> +endif
> +
>  # Compilation. We make sure the kernel gets rebuilt when the
>  # configuration has changed. We call the 'all' and
>  # '$(LINUX_TARGET_NAME)' targets separately because calling them in
> @@ -503,6 +509,7 @@ define LINUX_BUILD_CMDS
>  	$(LINUX_MAKE_ENV) $(BR2_MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) all
>  	$(LINUX_MAKE_ENV) $(BR2_MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) $(LINUX_TARGET_NAME)
>  	$(LINUX_BUILD_DTB)
> +	$(LINUX_BUILD_GDB_SCRIPTS)
>  	$(LINUX_APPEND_DTB)
>  endef
>  
> -- 
> 2.40.1
> 
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