Re: [PATCH v2 2/4] selftests: Fix seccomp to support relocatable build (O=objdir)

[Shuah Khan]

On 3/5/20 10:42 AM, Kees Cook wrote:
> On Thu, Mar 05, 2020 at 09:41:34AM -0700, Shuah Khan wrote:
> > On 3/4/20 7:20 PM, Kees Cook wrote:
> > > Instead of the TEST_CUSTOM_PROGS+all dance, you can just add an explicit
> > > dependency, with the final seccomp/Makefile looking like this:
> > >
> > >
> > > # SPDX-License-Identifier: GPL-2.0
> > > CFLAGS += -Wl,-no-as-needed -Wall
> > > LDFLAGS += -lpthread
> > >
> > > TEST_GEN_PROGS := seccomp_bpf seccomp_benchmark
> >
> > TEST_CUSTOM_PROGS is for differentiating test programs that
> > can't use lib.mk generic rules. It is appropriate to use
> > for seccomp_bpf
>
> I don't follow? This suggested Makefile works for me (i.e. it can use
> the lib.mk generic rules since CFLAGS and LDFLAGS can be customized
> first, and it just adds an additional dependency).

Yeah. TEST_CUSTOM_PROGS isn't really needed for this custom case.
I can refine it and get rid of the dependency.

> > > include ../lib.mk
> > >
> > > # Additional dependencies
> > > $(OUTPUT)/seccomp_bpf: ../kselftest_harness.h
>
> BTW, I see a lot of other targets that use kselftest_harness.h appear to
> be missing this Makefile dependency, but that's a different problem. :)
>
> > > (Though this fails in the same way as above when run from the top-level
> > > directory.)
> >
> > I didn't see this because I have been the same directory I used
> > for relocated cross-build kernel. :(
> >
> > Thanks for testing this. I know the problem here. all is a dependency
> > for install step and $(OUTPUT) is referencing the objdir before it
> > gets created. It is a Makefile/lib.mk problem to fix.

I was way off with my analysis. :(

> > I will do a separate patch for this. This will show up in any test
> > that is using $(OUTPUT) to relocate objects mainly the ones that
> > require custom build rule like seeccomp.
>
> Okay, cool. It looked to me like it lost track of the top level source
> directory (i.e. "make: entering $output" ... "can't find
> ../other/files")

Odd that you would have empty objdir in the cross-compile case.

In the cross-compile case, you would have cross-built kernel first in
the object directory. Your objdir won't be empty.

This is no different from kselftest build dependency on kernel build
even when srcdir=objdir

So for cross-build case, the following  is the workflow to build kernel
first and then the tests:

make O=/../objdir ARCH=arm64 HOSTCC=gcc CROSS_COMPILE=aarch64-linux-gnu- 
defconfig

make O=/../objdir ARCH=arm64 HOSTCC=gcc CROSS_COMPILE=aarch64-linux-gnu- all

make kselftest-install O=/../objdir ARCH=arm64 HOSTCC=gcc 
CROSS_COMPILE=aarch64-linux-gnu- TARGETS=seccomp

You can isolate a single test when you are do native build:

make kselftest-install O=/../objdir TARGETS=seccomp

The above won't fail even if objdir doesn't exist and/or empty.

thanks,
-- Shuah