[PATCH] bpf/core.c - silence warning messages

Compiling kernel/bpf/core.c with W=1 causes a flood of warnings:

kernel/bpf/core.c:1198:65: warning: initialized field overwritten [-Woverride-init]
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~
kernel/bpf/core.c:1198:65: note: (near initialization for 'public_insntable[12]')
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~

98 copies of the above.

The attached patch silences the warnings, because we *know* we're overwriting
the default initializer. That leaves bpf/core.c with only 6 other warnings,
which become more visible in comparison.

Signed-off-by: Valdis Kletnieks <redacted>

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 4c2fa3ac56f6..2606665f2cb5 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile

@@ -21,3 +21,4 @@ obj-$(CONFIG_CGROUP_BPF) += cgroup.o
 ifeq ($(CONFIG_INET),y)
 obj-$(CONFIG_BPF_SYSCALL) += reuseport_array.o
 endif
+CFLAGS_core.o          += $(call cc-disable-warning, override-init)

On Sun, Jan 27, 2019 at 8:43 PM [off-list ref] wrote:

Compiling kernel/bpf/core.c with W=1 causes a flood of warnings:

kernel/bpf/core.c:1198:65: warning: initialized field overwritten [-Woverride-init]
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~
kernel/bpf/core.c:1198:65: note: (near initialization for 'public_insntable[12]')
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~

98 copies of the above.

The attached patch silences the warnings, because we *know* we're overwriting
the default initializer. That leaves bpf/core.c with only 6 other warnings,
which become more visible in comparison.

My concern is that this will also mute the warning for other parts of
bpf/core.c.

Maybe we should move bpf_opcode_in_insntable() to a separate file, and mute
warning for that file?

Daniel and Alexei, what do you think?

Thanks,
Song

On 01/28/2019 06:18 PM, Song Liu wrote:

On Sun, Jan 27, 2019 at 8:43 PM [off-list ref] wrote:

quoted

Compiling kernel/bpf/core.c with W=1 causes a flood of warnings:

kernel/bpf/core.c:1198:65: warning: initialized field overwritten [-Woverride-init]
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~
kernel/bpf/core.c:1198:65: note: (near initialization for 'public_insntable[12]')
 1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
      |                                                                 ^~~~
kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
 1087 |  INSN_3(ALU, ADD,  X),   \
      |  ^~~~~~
kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
 1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
      |   ^~~~~~~~~~~~

98 copies of the above.

The attached patch silences the warnings, because we *know* we're overwriting
the default initializer. That leaves bpf/core.c with only 6 other warnings,
which become more visible in comparison.

My concern is that this will also mute the warning for other parts of
bpf/core.c.

Agree, valid concern.

Maybe we should move bpf_opcode_in_insntable() to a separate file, and mute
warning for that file?

I think moving in separate file would be overkill, imho. However, lets get
the kdoc and prototype warning fixed.

Thanks,
Daniel

On Mon, 28 Jan 2019 09:18:45 -0800, Song Liu said:

On Sun, Jan 27, 2019 at 8:43 PM [off-list ref] wrote:

quoted

The attached patch silences the warnings, because we *know* we're overwriting
the default initializer. That leaves bpf/core.c with only 6 other warnings,
which become more visible in comparison.

My concern is that this will also mute the warning for other parts of
bpf/core.c.

I checked and there weren't any warnings for other parts of the file.  Also, this message
doesn't even happen unless you build with W=1, which apparently happens so rarely
that nobody else has submitted a patch.

Is there a high likelihood that another overwrite of an initializer is going to
be included in the source?

Maybe we should move bpf_opcode_in_insntable() to a separate file, and mute
warning for that file?

Seems to be overkill - the intent of this patch was mostly to make the *other*
warnings issued with W=1 more noticable.

On Tue, 29 Jan 2019 00:22:26 +0100, Daniel Borkmann said:

I think moving in separate file would be overkill, imho. However, lets get
the kdoc and prototype warning fixed.

I have a bunch of spare time at the moment, so the kdoc and prototype
warnings are on my to-do list.

On 01/29/2019 12:48 AM, valdis.kletnieks@vt.edu wrote:

On Tue, 29 Jan 2019 00:22:26 +0100, Daniel Borkmann said:

quoted

I think moving in separate file would be overkill, imho. However, lets get
the kdoc and prototype warning fixed.

I have a bunch of spare time at the moment, so the kdoc and prototype
warnings are on my to-do list.

Great, thanks!

On Mon, Jan 28, 2019 at 3:35 PM [off-list ref] wrote:

On Mon, 28 Jan 2019 09:18:45 -0800, Song Liu said:

quoted

On Sun, Jan 27, 2019 at 8:43 PM [off-list ref] wrote:

quoted

quoted

The attached patch silences the warnings, because we *know* we're overwriting
the default initializer. That leaves bpf/core.c with only 6 other warnings,
which become more visible in comparison.

My concern is that this will also mute the warning for other parts of
bpf/core.c.

I checked and there weren't any warnings for other parts of the file.  Also, this message
doesn't even happen unless you build with W=1, which apparently happens so rarely
that nobody else has submitted a patch.

Is there a high likelihood that another overwrite of an initializer is going to
be included in the source?

quoted

Maybe we should move bpf_opcode_in_insntable() to a separate file, and mute
warning for that file?

Seems to be overkill - the intent of this patch was mostly to make the *other*
warnings issued with W=1 more noticable.

Yeah, I also felt this might be overkill while asking initially.

Acked-by: Song Liu <redacted>