On Wed, Jan 15, 2020 at 2:06 PM Toke Høiland-Jørgensen toke@redhat.com wrote:
Andrii Nakryiko andrii.nakryiko@gmail.com writes:
On Wed, Jan 15, 2020 at 6:13 AM Toke Høiland-Jørgensen toke@redhat.com wrote:
From: Toke Høiland-Jørgensen toke@redhat.com
The runqslower tool refuses to build without a file to read vmlinux BTF from. The build fails with an error message to override the location by setting the VMLINUX_BTF variable if autodetection fails. However, the Makefile doesn't actually work with that override - the error message is still emitted.
Do you have example command with VMLINUX_BTF override that didn't work (and what error message was emitted)?
Before this patch:
$ cd ~/build/linux/tools/bpf/runqslower $ make Makefile:18: *** "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly". Stop.
$ make VMLINUX_BTF=~/build/linux/vmlinux Makefile:18: *** "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly". Stop.
Ok, so this is strange. Try make clean and run with V=1, it might help to debug this. This could happen if ~/build/linux/vmlinux doesn't exist, but I assume you double-checked that. It works for me just fine (Makefile won't do VMLINUX_BTF := assignment, if it's defined through make invocation, so your change should be a no-op in that regard):
$ make clean $ make VMLINUX_BTF=~/linux-build/default/vmlinux V=1 ... .output/sbin/bpftool btf dump file ~/linux-build/default/vmlinux format c > .output/vmlinux.h ...
Wonder what your output looks like?
Fix this by only doing auto-detection if no override is set. And while we're at it, also look for a vmlinux file in the current kernel build dir if none if found on the running kernel.
Fixes: 9c01546d26d2 ("tools/bpf: Add runqslower tool to tools/bpf") Signed-off-by: Toke Høiland-Jørgensen toke@redhat.com
tools/bpf/runqslower/Makefile | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile index cff2fbcd29a8..fb93ce2bf2fe 100644 --- a/tools/bpf/runqslower/Makefile +++ b/tools/bpf/runqslower/Makefile @@ -10,12 +10,16 @@ CFLAGS := -g -Wall
# Try to detect best kernel BTF source KERNEL_REL := $(shell uname -r) -ifneq ("$(wildcard /sys/kernel/btf/vmlinux)","") -VMLINUX_BTF := /sys/kernel/btf/vmlinux -else ifneq ("$(wildcard /boot/vmlinux-$(KERNEL_REL))","") -VMLINUX_BTF := /boot/vmlinux-$(KERNEL_REL) -else -$(error "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly") +ifeq ("$(VMLINUX_BTF)","")
- ifneq ("$(wildcard /sys/kernel/btf/vmlinux)","")
- VMLINUX_BTF := /sys/kernel/btf/vmlinux
- else ifneq ("$(wildcard /boot/vmlinux-$(KERNEL_REL))","")
- VMLINUX_BTF := /boot/vmlinux-$(KERNEL_REL)
- else ifneq ("$(wildcard $(abspath ../../../vmlinux))","")
- VMLINUX_BTF := $(abspath ../../../vmlinux)
I'm planning to mirror runqslower into libbpf Github repo and this ../../../vmlinux piece will be completely out of place in that context. Also it only will help when building kernel in-tree. So I'd rather not add this.
Well building the kernel in-tree is something people sometimes want to do ;)
Specifically, the selftests depend on this, so we should at least fix those; but I guess it could work to just pass in VMLINUX_BTF as part of the make -C from the selftests dir? I'll try that...
Yes, it can be handled through VMLINUX_BTF override for selftests. As I said, this will be a self-contained example in libbpf's Github repo, so this "in kernel tree" assumption doesn't stand there.
-Toke