bpf: silence warning messages in core [Linux 4.4.187]

This Linux kernel change "bpf: silence warning messages in core" is included in the Linux 4.4.187 release. This change is authored by Valdis Klētnieks <valdis.kletnieks [at] vt.edu> on Thu Jun 6 22:39:27 2019 -0400. The commit for this change in Linux stable tree is 7dd2dc6 (patch) which is from upstream commit aee450c. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream aee450c.

bpf: silence warning messages in core

[ Upstream commit aee450cbe482a8c2f6fa5b05b178ef8b8ff107ca ]

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 <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

There is one line of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 kernel/bpf/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 13272582..677991f 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -1,4 +1,5 @@
 obj-y := core.o
+CFLAGS_core.o += $(call cc-disable-warning, override-init)

 obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o

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