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* [PATCH v2 bpf-next] bpf: Fix build without BPF_SYSCALL, but with BPF_JIT.
@ 2020-08-31 15:51 Alexei Starovoitov
  2020-08-31 16:15 ` Paul E. McKenney
  2020-08-31 20:07 ` Daniel Borkmann
  0 siblings, 2 replies; 4+ messages in thread
From: Alexei Starovoitov @ 2020-08-31 15:51 UTC (permalink / raw)
  To: davem; +Cc: daniel, paulmck, netdev, bpf, kernel-team

From: Alexei Starovoitov <ast@kernel.org>

When CONFIG_BPF_SYSCALL is not set, but CONFIG_BPF_JIT=y
the kernel build fails:
In file included from ../kernel/bpf/trampoline.c:11:
../kernel/bpf/trampoline.c: In function ‘bpf_trampoline_update’:
../kernel/bpf/trampoline.c:220:39: error: ‘call_rcu_tasks_trace’ undeclared
../kernel/bpf/trampoline.c: In function ‘__bpf_prog_enter_sleepable’:
../kernel/bpf/trampoline.c:411:2: error: implicit declaration of function ‘rcu_read_lock_trace’
../kernel/bpf/trampoline.c: In function ‘__bpf_prog_exit_sleepable’:
../kernel/bpf/trampoline.c:416:2: error: implicit declaration of function ‘rcu_read_unlock_trace’

This is due to:
obj-$(CONFIG_BPF_JIT) += trampoline.o
obj-$(CONFIG_BPF_JIT) += dispatcher.o
There is a number of functions that arch/x86/net/bpf_jit_comp.c is
using from these two files, but none of them will be used when
only cBPF is on (which is the case for BPF_SYSCALL=n BPF_JIT=y).

Add rcu_trace functions to rcupdate_trace.h. The JITed code won't execute them
and BPF trampoline logic won't be used without BPF_SYSCALL.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/rcupdate_trace.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index d9015aac78c6..aaaac8ac927c 100644
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -82,7 +82,14 @@ static inline void rcu_read_unlock_trace(void)
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
 void synchronize_rcu_tasks_trace(void);
 void rcu_barrier_tasks_trace(void);
-
+#else
+/*
+ * The BPF JIT forms these addresses even when it doesn't call these
+ * functions, so provide definitions that result in runtime errors.
+ */
+static inline void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) { BUG(); }
+static inline void rcu_read_lock_trace(void) { BUG(); }
+static inline void rcu_read_unlock_trace(void) { BUG(); }
 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
 
 #endif /* __LINUX_RCUPDATE_TRACE_H */
-- 
2.23.0


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2020-08-31 20:07 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-31 15:51 [PATCH v2 bpf-next] bpf: Fix build without BPF_SYSCALL, but with BPF_JIT Alexei Starovoitov
2020-08-31 16:15 ` Paul E. McKenney
2020-08-31 16:19   ` Alexei Starovoitov
2020-08-31 20:07 ` Daniel Borkmann

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