[PATCH bpf-next 0/3] samples/bpf: Allow building as PIE

[PATCH bpf-next 0/3] samples/bpf: Allow building as PIE

[Viktor Malik]

Hi,

when trying to build samples/bpf as PIE in Fedora, we came across
several issues, mainly related to the way compiler/linker flags are
handled in samples/bpf/Makefile. The first 2 commits in this patchset
address these issues (see commit messages for details).

At the same time, this proposes to allow passing an already built
bpftool to samples/bpf/Makefile. The reason is to remove a redundant
build step but also because I was not able to find a correct combination
of build flags to build libbpf.a for samples/bpf/bpftool/ with -fPIE.

Viktor Malik (3):
  samples/bpf: Allow building with custom CFLAGS/LDFLAGS
  samples/bpf: Fix passing LDFLAGS to libbpf
  samples/bpf: Allow building with custom bpftool

 samples/bpf/Makefile | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

-- 
2.41.0

[PATCH bpf-next 1/3] samples/bpf: Allow building with custom CFLAGS/LDFLAGS

[Viktor Malik]

Currently, it is not possible to specify custom flags when building
samples/bpf. The flags are defined in TPROGS_CFLAGS/TPROGS_LDFLAGS
variables, however, when trying to override those from the make command,
compilation fails.

For example, when trying to build with PIE:

    $ make -C samples/bpf TPROGS_CFLAGS="-fpie" TPROGS_LDFLAGS="-pie"

This is because samples/bpf/Makefile updates these variables, especially
appends include paths to TPROGS_CFLAGS and these updates are overridden
by setting the variables from the make command.

This patch introduces variables TPROGS_USER_CFLAGS/TPROGS_USER_LDFLAGS
for this purpose, which can be set from the make command and their
values are propagated to TPROGS_CFLAGS/TPROGS_LDFLAGS.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
---
 samples/bpf/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 90af76fa9dd8..5a9805edec93 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -150,6 +150,9 @@ always-y += ibumad_kern.o
 always-y += hbm_out_kern.o
 always-y += hbm_edt_kern.o
 
+TPROGS_CFLAGS = $(TPROGS_USER_CFLAGS)
+TPROGS_LDFLAGS = $(TPROGS_USER_LDFLAGS)
+
 ifeq ($(ARCH), arm)
 # Strip all except -D__LINUX_ARM_ARCH__ option needed to handle linux
 # headers when arm instruction set identification is requested.
@@ -316,7 +319,7 @@ XDP_SAMPLE_CFLAGS += -Wall -O2 \
 		     -I$(LIBBPF_INCLUDE) \
 		     -I$(src)/../../tools/testing/selftests/bpf
 
-$(obj)/$(XDP_SAMPLE): TPROGS_CFLAGS = $(XDP_SAMPLE_CFLAGS)
+$(obj)/$(XDP_SAMPLE): TPROGS_CFLAGS = $(XDP_SAMPLE_CFLAGS) $(TPROGS_USER_CFLAGS)
 $(obj)/$(XDP_SAMPLE): $(src)/xdp_sample_user.h $(src)/xdp_sample_shared.h
 # Override includes for trace_helpers.o because __must_check won't be defined
 # in our include path.
-- 
2.41.0

[PATCH bpf-next 2/3] samples/bpf: Fix passing LDFLAGS to libbpf

[Viktor Malik]

samples/bpf/Makefile passes LDFLAGS=$(TPROGS_LDFLAGS) to libbpf build
without surrounding quotes, which may cause compilation errors when
passing custom TPROGS_USER_LDFLAGS.

For example:

    $ make -C samples/bpf/ TPROGS_USER_LDFLAGS="-Wl,--as-needed -specs=/usr/lib/gcc/x86_64-redhat-linux/13/libsanitizer.spec"
    make: Entering directory './samples/bpf'
    make -C ../../ M=./samples/bpf BPF_SAMPLES_PATH=./samples/bpf
    make[1]: Entering directory '.'
    make -C ./samples/bpf/../../tools/lib/bpf RM='rm -rf' EXTRA_CFLAGS="-Wall -O2 -Wmissing-prototypes -Wstrict-prototypes  -I./usr/include -I./tools/testing/selftests/bpf/ -I./samples/bpf/libbpf/include -I./tools/include -I./tools/perf -I./tools/lib -DHAVE_ATTR_TEST=0" \
            LDFLAGS=-Wl,--as-needed -specs=/usr/lib/gcc/x86_64-redhat-linux/13/libsanitizer.spec srctree=./samples/bpf/../../ \
            O= OUTPUT=./samples/bpf/libbpf/ DESTDIR=./samples/bpf/libbpf prefix= \
            ./samples/bpf/libbpf/libbpf.a install_headers
    make: invalid option -- 'c'
    make: invalid option -- '='
    make: invalid option -- '/'
    make: invalid option -- 'u'
    make: invalid option -- '/'
    [...]

Fix the error by properly quoting $(TPROGS_LDFLAGS).

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Suggested-by: Donald Zickus <dzickus@redhat.com>
---
 samples/bpf/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 5a9805edec93..378b9f3e9321 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -254,7 +254,7 @@ clean:
 $(LIBBPF): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUTPUT)
 # Fix up variables inherited from Kbuild that tools/ build system won't like
 	$(MAKE) -C $(LIBBPF_SRC) RM='rm -rf' EXTRA_CFLAGS="$(TPROGS_CFLAGS)" \
-		LDFLAGS=$(TPROGS_LDFLAGS) srctree=$(BPF_SAMPLES_PATH)/../../ \
+		LDFLAGS="$(TPROGS_LDFLAGS)" srctree=$(BPF_SAMPLES_PATH)/../../ \
 		O= OUTPUT=$(LIBBPF_OUTPUT)/ DESTDIR=$(LIBBPF_DESTDIR) prefix= \
 		$@ install_headers
 
-- 
2.41.0

[PATCH bpf-next 3/3] samples/bpf: Allow building with custom bpftool

[Viktor Malik]

samples/bpf build its own bpftool boostrap to generate vmlinux.h as well
as some BPF objects. This is a redundant step if bpftool has been
already built, so update samples/bpf/Makefile such that it accepts a
path to bpftool passed via the BPFTOOL variable. The approach is
practically the same as tools/testing/selftests/bpf/Makefile uses.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
---
 samples/bpf/Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 378b9f3e9321..933f6c3fe6b0 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -260,8 +260,9 @@ $(LIBBPF): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
 
 BPFTOOLDIR := $(TOOLS_PATH)/bpf/bpftool
 BPFTOOL_OUTPUT := $(abspath $(BPF_SAMPLES_PATH))/bpftool
-BPFTOOL := $(BPFTOOL_OUTPUT)/bootstrap/bpftool
-$(BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT)
+DEFAULT_BPFTOOL := $(BPFTOOL_OUTPUT)/bootstrap/bpftool
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT)
 	$(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../ 		\
 		OUTPUT=$(BPFTOOL_OUTPUT)/ bootstrap
 
-- 
2.41.0

Re: [PATCH bpf-next 0/3] samples/bpf: Allow building as PIE

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Wed, 25 Oct 2023 08:19:11 +0200 you wrote:
> Hi,
> 
> when trying to build samples/bpf as PIE in Fedora, we came across
> several issues, mainly related to the way compiler/linker flags are
> handled in samples/bpf/Makefile. The first 2 commits in this patchset
> address these issues (see commit messages for details).
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/3] samples/bpf: Allow building with custom CFLAGS/LDFLAGS
    https://git.kernel.org/bpf/bpf-next/c/870f09f1ba30
  - [bpf-next,2/3] samples/bpf: Fix passing LDFLAGS to libbpf
    https://git.kernel.org/bpf/bpf-next/c/f56bcfadf7d6
  - [bpf-next,3/3] samples/bpf: Allow building with custom bpftool
    https://git.kernel.org/bpf/bpf-next/c/37db10bc247d

You are awesome, thank you!
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