Re: linux-next: build failure after merge of the net-next tree

David Miller
2018-01-12T03:12:00Z

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Wed, 10 Jan 2018 17:58:54 -0800

> On Thu, Jan 11, 2018 at 11:53:55AM +1100, Stephen Rothwell wrote:
>> Hi all,
>>
>> After merging the net-next tree, today's linux-next build (x86_64
>> allmodconfig) failed like this:
>>
>> kernel/bpf/verifier.o: In function `bpf_check':
>> verifier.c:(.text+0xd86e): undefined reference to `bpf_patch_call_args'
>>
>> Caused by commit
>>
>> 1ea47e01ad6e ("bpf: add support for bpf_call to interpreter")
>>
>> interacting with commit
>>
>> 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config")
>>
>> from the bpf and net trees.
>>
>> I have just reverted commit 290af86629b2 for today. A better solution
>> would be nice (lie fixing this in a merge between the net-next and net
>> trees).
>
> that's due to 'endif' from 290af86629b2 needs to be moved above
> bpf_patch_call_args() definition.

That doesn't fix it, because then you'd need to expose
interpreters_args as well and obviously that can't be right.

Instead, we should never call bpf_patch_call_args() when JIT always on
is enabled. So if we fail to JIT the subprogs we should fail
immediately.

This is the net --> net-next merge resolution I am about to use to fix
this:

...
+static int fixup_call_args(struct bpf_verifier_env *env)
+{
+ struct bpf_prog *prog = env->prog;
+ struct bpf_insn *insn = prog->insnsi;
- int i, depth;
++ int i, depth, err;
+
- if (env->prog->jit_requested)
- if (jit_subprogs(env) == 0)
++ err = 0;
++ if (env->prog->jit_requested) {
++ err = jit_subprogs(env);
++ if (err == 0)
+ return 0;
-
++ }
++#ifndef CONFIG_BPF_JIT_ALWAYS_ON
+ for (i = 0; i < prog->len; i++, insn++) {
+ if (insn->code != (BPF_JMP | BPF_CALL) ||
+ insn->src_reg != BPF_PSEUDO_CALL)
+ continue;
+ depth = get_callee_stack_depth(env, insn, i);
+ if (depth < 0)
+ return depth;
+ bpf_patch_call_args(insn, depth);
+ }
- return 0;
++ err = 0;
++#endif
++ return err;
+}
+
/* fixup insn->imm field of bpf_call instructions
* and inline eligible helpers as explicit sequence of BPF instructions
*