From 055f48d1d602be99b04fffe8e2aa8d9481fe10a5 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Mon, 27 Jun 2022 17:15:37 +0200
Subject: [PATCH] Probe instruction set

Kernel supports few instruction sets [1], and the default one (which is
apparently being used at the moment in falco) is going to be the
`generic` or `v1`, which has certain limitations and requires
workarounds. It's possible to instruct `llc` to search the latest
supported instruction set via `-mcpu` parameter, which generally
speaking should result in more compact and potentially more performant
generated instructions for the same code. For the support table see
great blog post [2] about the topic. The gist for the support is:

v2: Linux v4.14 [3], LLVM v6.0 [4]
v3: Linux v5.1 [5], LLVM [6]

[1]: https://www.kernel.org/doc/html/latest/bpf/bpf_devel_QA.html#q-new-bpf-instruction-for-kernel-and-llvm
[2]: https://pchaigno.github.io/bpf/2021/10/20/ebpf-instruction-sets.html
[3]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=92b31a9af73b3a3fc801899335d6c47966351830
[4]: https://reviews.llvm.org/rL311522
[5]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=092ed0968bb648cd18e8a0430cd0a8a71727315c
[6]: https://reviews.llvm.org/rL353384
---
 driver/bpf/Makefile | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/driver/bpf/Makefile b/driver/bpf/Makefile
index 90516a4e1..5472fd468 100644
--- a/driver/bpf/Makefile
+++ b/driver/bpf/Makefile
@@ -64,4 +64,9 @@ $(obj)/probe.o: $(src)/probe.c \
 		-fno-stack-protector \
 		-Wno-tautological-compare \
 		-O2 $(BPF_DEBUG_SYMBOLS) -emit-llvm -c $< -o $(patsubst %.o,%.ll,$@)
-	$(LLC) -march=bpf -filetype=obj -o $@ $(patsubst %.o,%.ll,$@)
+	$(LLC) \
+		-march=bpf \
+		-mcpu=probe \
+		-mattr=+alu32 \
+		-filetype=obj \
+		-o $@ $(patsubst %.o,%.ll,$@)