Re: [PATCH v6 bpf-next 17/17] selftests/bpf: add C-level selftests for indirect jumps

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 25/10/21 05:27PM, Eduard Zingerman wrote:
> On Sun, 2025-10-19 at 20:21 +0000, Anton Protopopov wrote:
> 
> [...]
> 
> > diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c b/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c
> > new file mode 100644
> > index 000000000000..4394654ac75a
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c
> > @@ -0,0 +1,185 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <test_progs.h>
> > +
> > +#include <linux/if_ether.h>
> > +#include <linux/in.h>
> > +#include <linux/ip.h>
> > +#include <linux/ipv6.h>
> > +#include <linux/in6.h>
> > +#include <linux/udp.h>
> > +#include <linux/tcp.h>
> > +
> > +#include <sys/syscall.h>
> > +#include <bpf/bpf.h>
> > +
> > +#include "bpf_gotox.skel.h"
> > +
> > +/* Disable tests for now, as CI runs with LLVM-20 */
> > +#if 0
> 
> I removed all the `#if 0` and tried to compile this test using LLVM at commit
> 1a9aba29b09e ("[RISCV] Remove unreachable break statements. NFC (#164481)").
> 
> LLVM refuses to compile showing errors like below:
> 
>   CLNG-BPF [test_progs-cpuv4] bpf_gotox.bpf.o
> fatal error: error in backend: Cannot select: <U+001B>[0;31mt15<U+001B>[0m: ch = brind <U+001B>[0;30mt7<U+001B>[0m, <U+001B>[0;30mt14<U+001B>[0m
>   <U+001B>[0;30mt14<U+001B>[0m: i64,ch = load<(invariant load (s64) from %ir.arrayidx)> <U+001B>[0;30mt0<U+001B>[0m, <U+001B>[0;36mt13<U+001B>[0m, undef:i64, progs/bpf_gotox.c:202:8
>     <U+001B>[0;36mt13<U+001B>[0m: i64 = add nuw <U+001B>[0;33mt17<U+001B>[0m, <U+001B>[0;35mt12<U+001B>[0m, progs/bpf_gotox.c:202:8
>       <U+001B>[0;33mt17<U+001B>[0m: i64 = LDIMM64 TargetGlobalAddress:i64<ptr @__const.big_jump_table.jt> 0, progs/bpf_gotox.c:202:8
>       <U+001B>[0;35mt12<U+001B>[0m: i64 = shl nuw nsw <U+001B>[0;32mt9<U+001B>[0m, Constant:i64<3>, progs/bpf_gotox.c:202:8
>         <U+001B>[0;32mt9<U+001B>[0m: i64 = and <U+001B>[0;35mt5<U+001B>[0m, Constant:i64<255>, progs/bpf_gotox.c:202:18
>           <U+001B>[0;35mt5<U+001B>[0m: i64,ch = load<(load (s64) from %ir.ctx)> <U+001B>[0;30mt0<U+001B>[0m, <U+001B>[0;32mt2<U+001B>[0m, undef:i64, progs/bpf_gotox.c:202:16
>             <U+001B>[0;32mt2<U+001B>[0m: i64,ch = CopyFromReg <U+001B>[0;30mt0<U+001B>[0m, Register:i64 %5
> In function: big_jump_table
> 
> CC'ing Yonghong.

Looks like no -mcpu=v4. I had to hack Makefile (set v3 -> v4) to build it.

Even when one tries to build test_progs-cpuv4, the v3 version is
also built.  In the bpf prog this is easy to ifdef it: x86_64 +
__clang + one can define a variable like BPF_CPU=4 in Makefile.
But the prog_tests can't easily see was the skeleton compiled
with v3 or v4, so I just ended up with putting #if 0 there for now...

> [...]