[Buildroot] [PATCH v2] toolchain: add gdb wrapper that automatically passes the gdbinit file

[Buildroot] [PATCH v2] toolchain: add gdb wrapper that automatically passes the gdbinit file

[Thomas De Schampheleire]

From: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>

Buildroot already provided a gdbinit file to set the right sysroot, but
required users to pass this file explicitly when invoking gdb.

Make the process a bit more user-friendly by creating a gdb wrapper that
passes the gdbinit file to the real gdb program.

The code needs to take into account several cases (internal toolchain,
external toolchain, ...) because the name and type of the real gdb program
differs.

The documentation is updated to reflect this change.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
---
v2:
- use "$@" instead of $@ in shell wrapper
- update release in manual to match 2016.05

 docs/manual/using-buildroot-debugger.txt           |  7 +++--
 package/gdb/gdb.mk                                 |  2 +-
 toolchain/helpers.mk                               | 36 +++++++++++++++++++---
 toolchain/toolchain-external/toolchain-external.mk | 10 +++---
 4 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/docs/manual/using-buildroot-debugger.txt b/docs/manual/using-buildroot-debugger.txt
index b5063ca..c3a1215 100644
--- a/docs/manual/using-buildroot-debugger.txt
+++ b/docs/manual/using-buildroot-debugger.txt
@@ -35,7 +35,7 @@ Then, on the host, you should start the cross gdb using the following
 command line:
 
 ----------------------------
-<buildroot>/output/host/usr/bin/<tuple>-gdb -x <buildroot>/output/staging/usr/share/buildroot/gdbinit foo
+<buildroot>/output/host/usr/bin/<tuple>-gdb foo
 ----------------------------
 
 Of course, +foo+ must be available in the current directory, built
@@ -43,8 +43,9 @@ with debugging symbols. Typically you start this command from the
 directory where +foo+ is built (and not from +output/target/+ as the
 binaries in that directory are stripped).
 
-The +<buildroot>/output/staging/usr/share/buildroot/gdbinit+ file will tell the
-cross gdb where to find the libraries of the target.
+Since Buildroot 2016.05, the above gdb program is actually a wrapper script
+that passes a gdbinit file. The gdbinit file tells the cross gdb where to find
+the libraries of the target.
 
 Finally, to connect to the target from the cross gdb:
 
diff --git a/package/gdb/gdb.mk b/package/gdb/gdb.mk
index 0a7af1e..5edb1aa 100644
--- a/package/gdb/gdb.mk
+++ b/package/gdb/gdb.mk
@@ -187,7 +187,7 @@ endef
 
 HOST_GDB_POST_INSTALL_HOOKS += HOST_GDB_ADD_SYMLINK
 
-HOST_GDB_POST_INSTALL_HOOKS += gen_gdbinit_file
+HOST_GDB_POST_INSTALL_HOOKS += setup_gdb_wrapper
 
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))
diff --git a/toolchain/helpers.mk b/toolchain/helpers.mk
index d28a2ca..be649f3 100644
--- a/toolchain/helpers.mk
+++ b/toolchain/helpers.mk
@@ -387,8 +387,36 @@ check_unusable_toolchain = \
 	fi
 
 #
-# Generate gdbinit file for use with Buildroot
-#
-gen_gdbinit_file = \
+# Create a gdb wrapper that sources a minimal gdbinit file. We don't need to
+# create a gdbtui wrapper because that one actually calls gdb.
+# For internal toolchains:
+# - if BR2_PACKAGE_HOST_GDB is set, gdb is built by buildroot and a real file at
+#   $(TARGET_CROSS)gdb ( == $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb )
+# For external toolchains:
+# - if BR2_PACKAGE_HOST_GDB is not set, gdb is provided by the external
+#   toolchain and $(TARGET_CROSS)gdb is a symlink.
+# - if BR2_PACKAGE_HOST_GDB is set, gdb is built by buildroot and a real file at
+#   $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb
+#
+define setup_gdb_wrapper
 	mkdir -p $(STAGING_DIR)/usr/share/buildroot/ ; \
-	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit
+	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit ; \
+	if [ -f $(TARGET_CROSS)gdb -a ! -e $(TARGET_CROSS)gdb.real ]; then \
+		gdb_wrapper=$(TARGET_CROSS)gdb ; \
+		real_gdb=$${gdb_wrapper}.real ; \
+		mv $${gdb_wrapper} $${real_gdb} ; \
+	elif [ -L $(TARGET_CROSS)gdb ]; then \
+		gdb_wrapper=$(TARGET_CROSS)gdb ; \
+		real_gdb=`readlink -f $(TARGET_CROSS)gdb`; \
+		rm $(TARGET_CROSS)gdb ; \
+	elif [ -f $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb ]; then \
+		gdb_wrapper=$(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb ; \
+		real_gdb=$${gdb_wrapper}.real ; \
+		mv $${gdb_wrapper} $${real_gdb} ; \
+	fi ; \
+	if [ -n "$${gdb_wrapper}" ]; then \
+		echo "#!/bin/sh" > $${gdb_wrapper} ; \
+		echo "$${real_gdb} -x $(STAGING_DIR)/usr/share/buildroot/gdbinit \"\$$@\"" >> $${gdb_wrapper} ; \
+		chmod +x $${gdb_wrapper} ; \
+	fi
+endef
diff --git a/toolchain/toolchain-external/toolchain-external.mk b/toolchain/toolchain-external/toolchain-external.mk
index 2422b6d..b964d73 100644
--- a/toolchain/toolchain-external/toolchain-external.mk
+++ b/toolchain/toolchain-external/toolchain-external.mk
@@ -741,12 +741,12 @@ define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER
 endef
 
 #
-# Generate gdbinit file for use with Buildroot
+# Generate gdb wrapper and gdbinit file for use with Buildroot
 #
-define TOOLCHAIN_EXTERNAL_INSTALL_GDBINIT
+define TOOLCHAIN_EXTERNAL_INSTALL_GDB_WRAPPER
 	$(Q)if test -f $(TARGET_CROSS)gdb ; then \
-		$(call MESSAGE,"Installing gdbinit"); \
-		$(gen_gdbinit_file); \
+		$(call MESSAGE,"Creating gdb wrapper and gdbinit file"); \
+		$(setup_gdb_wrapper); \
 	fi
 endef
 
@@ -771,7 +771,7 @@ define TOOLCHAIN_EXTERNAL_INSTALL_STAGING_CMDS
 	$(TOOLCHAIN_EXTERNAL_INSTALL_SYSROOT_LIBS)
 	$(TOOLCHAIN_EXTERNAL_INSTALL_SYSROOT_LIBS_BFIN_FDPIC)
 	$(TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER)
-	$(TOOLCHAIN_EXTERNAL_INSTALL_GDBINIT)
+	$(TOOLCHAIN_EXTERNAL_INSTALL_GDB_WRAPPER)
 endef
 
 # Even though we're installing things in both the staging, the host
-- 
2.7.3

[Buildroot] [PATCH v2] toolchain: add gdb wrapper that automatically passes the gdbinit file

[Yann E. MORIN]

Thomas, All,

On 2016-04-29 20:03 +0200, Thomas De Schampheleire spake thusly:
> From: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
> 
> Buildroot already provided a gdbinit file to set the right sysroot, but
> required users to pass this file explicitly when invoking gdb.
> 
> Make the process a bit more user-friendly by creating a gdb wrapper that
> passes the gdbinit file to the real gdb program.
> 
> The code needs to take into account several cases (internal toolchain,
> external toolchain, ...) because the name and type of the real gdb program
> differs.
> 
> The documentation is updated to reflect this change.
> 
> Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
> ---
[--SNIP--]
> diff --git a/toolchain/helpers.mk b/toolchain/helpers.mk
> index d28a2ca..be649f3 100644
> --- a/toolchain/helpers.mk
> +++ b/toolchain/helpers.mk
> @@ -387,8 +387,36 @@ check_unusable_toolchain = \
>  	fi
>  
>  #
> -# Generate gdbinit file for use with Buildroot
> -#
> -gen_gdbinit_file = \
> +# Create a gdb wrapper that sources a minimal gdbinit file. We don't need to
> +# create a gdbtui wrapper because that one actually calls gdb.
> +# For internal toolchains:
> +# - if BR2_PACKAGE_HOST_GDB is set, gdb is built by buildroot and a real file at
> +#   $(TARGET_CROSS)gdb ( == $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb )
> +# For external toolchains:
> +# - if BR2_PACKAGE_HOST_GDB is not set, gdb is provided by the external
> +#   toolchain and $(TARGET_CROSS)gdb is a symlink.
> +# - if BR2_PACKAGE_HOST_GDB is set, gdb is built by buildroot and a real file at
> +#   $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb
> +#
> +define setup_gdb_wrapper
>  	mkdir -p $(STAGING_DIR)/usr/share/buildroot/ ; \
> -	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit
> +	echo "set sysroot $(STAGING_DIR)" > $(STAGING_DIR)/usr/share/buildroot/gdbinit ; \

You don't need a continuation line here.

> +	if [ -f $(TARGET_CROSS)gdb -a ! -e $(TARGET_CROSS)gdb.real ]; then \
> +		gdb_wrapper=$(TARGET_CROSS)gdb ; \
> +		real_gdb=$${gdb_wrapper}.real ; \
> +		mv $${gdb_wrapper} $${real_gdb} ; \
> +	elif [ -L $(TARGET_CROSS)gdb ]; then \
> +		gdb_wrapper=$(TARGET_CROSS)gdb ; \
> +		real_gdb=`readlink -f $(TARGET_CROSS)gdb`; \
> +		rm $(TARGET_CROSS)gdb ; \
> +	elif [ -f $(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb ]; then \
> +		gdb_wrapper=$(HOST_DIR)/usr/bin/$(GNU_TARGET_NAME)-gdb ; \
> +		real_gdb=$${gdb_wrapper}.real ; \
> +		mv $${gdb_wrapper} $${real_gdb} ; \
> +	fi ; \

I was surprised to see that we did not already have code to locate the
cross-gdb, especially for external toolchains...

I could not find where we copy gcc et al. either... :-/

> +	if [ -n "$${gdb_wrapper}" ]; then \
> +		echo "#!/bin/sh" > $${gdb_wrapper} ; \
> +		echo "$${real_gdb} -x $(STAGING_DIR)/usr/share/buildroot/gdbinit \"\$$@\"" >> $${gdb_wrapper} ; \

Please do not introduce another hard-coded abslute path. You should
derive the path to the gdbinit file relative to the gdb executable, if
at all possible.

Regards,
Yann E. MORIN.

-- 
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[Buildroot] [PATCH v2] toolchain: add gdb wrapper that automatically passes the gdbinit file

[Thomas Petazzoni]

Hello,

On Fri, 29 Apr 2016 20:03:07 +0200, Thomas De Schampheleire wrote:
> From: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
> 
> Buildroot already provided a gdbinit file to set the right sysroot, but
> required users to pass this file explicitly when invoking gdb.
> 
> Make the process a bit more user-friendly by creating a gdb wrapper that
> passes the gdbinit file to the real gdb program.
> 
> The code needs to take into account several cases (internal toolchain,
> external toolchain, ...) because the name and type of the real gdb program
> differs.
> 
> The documentation is updated to reflect this change.
> 
> Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
> ---
> v2:
> - use "$@" instead of $@ in shell wrapper
> - update release in manual to match 2016.05

After discussing at the Buildroot meeting, we decided to reject this
patch. Indeed, we believe this additional wrapper is not really needed,
and hides some more magic which we prefer to keep visible to the user.

What we could do is to make it a bit easier for users to find the
gdbinit file by having a "staging" symlink pointing to the sysroot,
installed in the host directory. This way, even if your toolchain is
installed in /opt/br-baz/, you can do:

/opt/br-baz/usr/bin/<blah>-gdb -x /opt/br-baz/usr/staging/usr/share/buildroot/gdbinit

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com