[PATCH bpf 0/2] samples: bpf: fix build issues with Clang/LLVM

Samples, at least XDP ones, can be built only with the compiler used
to build the kernel itself.
However, XDP sample infra introduced in Aug'21 was probably tested
with GCC/Binutils only as it's not really compilable for now with
Clang/LLVM.
These two are trivial fixes addressing this.

Alexander Lobakin (2):
  samples: bpf: fix xdp_sample_user.o linking with Clang
  samples: bpf: fix 'unknown warning group' build warning on Clang

 samples/bpf/Makefile          | 5 +++++
 samples/bpf/Makefile.target   | 2 +-
 samples/bpf/xdp_sample_user.h | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

-- 
2.33.1

Clang (13) doesn't get the jokes about specifying libraries to link in
cclags of individual .o objects:

clang-13: warning: -lm: 'linker' input unused [-Wunused-command-line-argument]
[ ... ]
  LD  samples/bpf/xdp_redirect_cpu
  LD  samples/bpf/xdp_redirect_map_multi
  LD  samples/bpf/xdp_redirect_map
  LD  samples/bpf/xdp_redirect
  LD  samples/bpf/xdp_monitor
/usr/bin/ld: samples/bpf/xdp_sample_user.o: in function `sample_summary_print':
xdp_sample_user.c:(.text+0x84c): undefined reference to `floor'
/usr/bin/ld: xdp_sample_user.c:(.text+0x870): undefined reference to `ceil'
/usr/bin/ld: xdp_sample_user.c:(.text+0x8cf): undefined reference to `floor'
/usr/bin/ld: xdp_sample_user.c:(.text+0x8f3): undefined reference to `ceil'
[ more ]

Specify '-lm' as ldflags for all xdp_sample_user.o users in the main
Makefile and remove it from ccflags of ^ in Makefile.target -- just
like it's done for all other samples. This works with all compilers.

Fixes: 6e1051a54e31 ("samples: bpf: Convert xdp_monitor to XDP samples helper")
Fixes: b926c55d856c ("samples: bpf: Convert xdp_redirect to XDP samples helper")
Fixes: e531a220cc59 ("samples: bpf: Convert xdp_redirect_cpu to XDP samples helper")
Fixes: bbe65865aa05 ("samples: bpf: Convert xdp_redirect_map to XDP samples helper")
Fixes: 594a116b2aa1 ("samples: bpf: Convert xdp_redirect_map_multi to XDP samples helper")
Signed-off-by: Alexander Lobakin <redacted>
---
 samples/bpf/Makefile        | 5 +++++
 samples/bpf/Makefile.target | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index a886dff1ba89..e5b049ad5447 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile

@@ -215,6 +215,11 @@ TPROGS_LDFLAGS := -L$(SYSROOT)/usr/lib
 endif
 
 TPROGS_LDLIBS			+= $(LIBBPF) -lelf -lz
+TPROGLDLIBS_xdp_monitor		+= -lm
+TPROGLDLIBS_xdp_redirect	+= -lm
+TPROGLDLIBS_xdp_redirect_cpu	+= -lm
+TPROGLDLIBS_xdp_redirect_map	+= -lm
+TPROGLDLIBS_xdp_redirect_map_multi += -lm
 TPROGLDLIBS_tracex4		+= -lrt
 TPROGLDLIBS_trace_output	+= -lrt
 TPROGLDLIBS_map_perf_test	+= -lrt

diff --git a/samples/bpf/Makefile.target b/samples/bpf/Makefile.target
index 5a368affa038..379560f11db4 100644
--- a/samples/bpf/Makefile.target
+++ b/samples/bpf/Makefile.target

@@ -76,7 +76,7 @@ $(tprog-cobjs): $(obj)/%.o: $(src)/%.c FORCE
 
 # Override includes for xdp_sample_user.o because $(srctree)/usr/include in
 # TPROGS_CFLAGS causes conflicts
-XDP_SAMPLE_CFLAGS += -Wall -O2 -lm \
+XDP_SAMPLE_CFLAGS += -Wall -O2 \
 		     -I./tools/include \
 		     -I./tools/include/uapi \
 		     -I./tools/lib \

-- 
2.33.1

Clang doesn't have 'stringop-truncation' group like GCC does, and
complains about it when building samples which use xdp_sample_user
infra:

 samples/bpf/xdp_sample_user.h:48:32: warning: unknown warning group '-Wstringop-truncation', ignored [-Wunknown-warning-option]
 #pragma GCC diagnostic ignored "-Wstringop-truncation"
                                ^
[ repeat ]

Those are harmless, but avoidable when guarding it with ifdef.
I could guard push/pop as well, but this would require one more
ifdef cruft around a single line which I don't think is reasonable.

Fixes: 156f886cf697 ("samples: bpf: Add basic infrastructure for XDP samples")
Signed-off-by: Alexander Lobakin <redacted>
---
 samples/bpf/xdp_sample_user.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/samples/bpf/xdp_sample_user.h b/samples/bpf/xdp_sample_user.h
index d97465ff8c62..5f44b877ecf5 100644
--- a/samples/bpf/xdp_sample_user.h
+++ b/samples/bpf/xdp_sample_user.h

@@ -45,7 +45,9 @@ const char *get_driver_name(int ifindex);
 int get_mac_addr(int ifindex, void *mac_addr);
 
 #pragma GCC diagnostic push
+#ifndef __clang__
 #pragma GCC diagnostic ignored "-Wstringop-truncation"
+#endif
 __attribute__((unused))
 static inline char *safe_strncpy(char *dst, const char *src, size_t size)
 {

-- 
2.33.1

On Sat, Dec 04, 2021 at 01:20:03AM IST, Alexander Lobakin wrote:

Clang (13) doesn't get the jokes about specifying libraries to link in
cclags of individual .o objects:

clang-13: warning: -lm: 'linker' input unused [-Wunused-command-line-argument]
[ ... ]
  LD  samples/bpf/xdp_redirect_cpu
  LD  samples/bpf/xdp_redirect_map_multi
  LD  samples/bpf/xdp_redirect_map
  LD  samples/bpf/xdp_redirect
  LD  samples/bpf/xdp_monitor
/usr/bin/ld: samples/bpf/xdp_sample_user.o: in function `sample_summary_print':
xdp_sample_user.c:(.text+0x84c): undefined reference to `floor'
/usr/bin/ld: xdp_sample_user.c:(.text+0x870): undefined reference to `ceil'
/usr/bin/ld: xdp_sample_user.c:(.text+0x8cf): undefined reference to `floor'
/usr/bin/ld: xdp_sample_user.c:(.text+0x8f3): undefined reference to `ceil'
[ more ]

Specify '-lm' as ldflags for all xdp_sample_user.o users in the main
Makefile and remove it from ccflags of ^ in Makefile.target -- just
like it's done for all other samples. This works with all compilers.

Fixes: 6e1051a54e31 ("samples: bpf: Convert xdp_monitor to XDP samples helper")
Fixes: b926c55d856c ("samples: bpf: Convert xdp_redirect to XDP samples helper")
Fixes: e531a220cc59 ("samples: bpf: Convert xdp_redirect_cpu to XDP samples helper")
Fixes: bbe65865aa05 ("samples: bpf: Convert xdp_redirect_map to XDP samples helper")
Fixes: 594a116b2aa1 ("samples: bpf: Convert xdp_redirect_map_multi to XDP samples helper")
Signed-off-by: Alexander Lobakin <redacted>
---

Thanks, something to remember to test for next time.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

--
Kartikeya

On Sat, Dec 04, 2021 at 01:20:04AM IST, Alexander Lobakin wrote:

Clang doesn't have 'stringop-truncation' group like GCC does, and
complains about it when building samples which use xdp_sample_user
infra:

 samples/bpf/xdp_sample_user.h:48:32: warning: unknown warning group '-Wstringop-truncation', ignored [-Wunknown-warning-option]
 #pragma GCC diagnostic ignored "-Wstringop-truncation"
                                ^
[ repeat ]

Those are harmless, but avoidable when guarding it with ifdef.
I could guard push/pop as well, but this would require one more
ifdef cruft around a single line which I don't think is reasonable.

Fixes: 156f886cf697 ("samples: bpf: Add basic infrastructure for XDP samples")
Signed-off-by: Alexander Lobakin <redacted>
---

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

[...]

--
Kartikeya

On Fri, Dec 3, 2021 at 11:55 AM Alexander Lobakin
[off-list ref] wrote:

Samples, at least XDP ones, can be built only with the compiler used
to build the kernel itself.
However, XDP sample infra introduced in Aug'21 was probably tested
with GCC/Binutils only as it's not really compilable for now with
Clang/LLVM.
These two are trivial fixes addressing this.

Alexander Lobakin (2):
  samples: bpf: fix xdp_sample_user.o linking with Clang
  samples: bpf: fix 'unknown warning group' build warning on Clang

There were conflicts when applying, but luckily I was the one who
caused this conflict in XDP_SAMPLE_CFLAGS, so I just fixed it up
locally and pushed to bpf-next. Thanks.

 samples/bpf/Makefile          | 5 +++++
 samples/bpf/Makefile.target   | 2 +-
 samples/bpf/xdp_sample_user.h | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

--
2.33.1