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[PATCH] nfp: bpf: improve handling for disabled BPF syscall

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  [PATCH] nfp: bpf: improve handling for disabled BPF syscall Arnd Bergmann <arnd@arndb.de> - 2016-09-23 22:30 +0200
    Re: [PATCH] nfp: bpf: improve handling for disabled BPF syscall Jakub Kicinski <jakub.kicinski@netronome.com> - 2016-09-25 18:00 +0200
    Re: [PATCH] nfp: bpf: improve handling for disabled BPF syscall David Miller <davem@davemloft.net> - 2016-09-26 08:30 +0200

#1490439 — [PATCH] nfp: bpf: improve handling for disabled BPF syscall

I stumbled over a new warning during randconfig testing,
with CONFIG_BPF_SYSCALL disabled:

drivers/net/ethernet/netronome/nfp/nfp_net_offload.c: In function 'nfp_net_bpf_offload':
drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: '*((void *)&res+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: 'res.n_instr' may be used uninitialized in this function [-Werror=maybe-uninitialized]

As far as I can tell, this is a false positive caused by the compiler
getting confused about a function that is partially inlined, but it's
easy to avoid while improving the code:

The nfp_bpf_jit() stub helper for that configuration is unusual as it
is defined in a header file but not marked 'static inline'. By moving
the compile-time check into the caller using the IS_ENABLED() macro,
we can remove that stub and simplify the nfp_net_bpf_offload_prepare()
function enough to unconfuse the compiler.

Fixes: 7533fdc0f77f ("nfp: bpf: add hardware bpf offload")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/netronome/nfp/nfp_bpf.h         | 10 ----------
 drivers/net/ethernet/netronome/nfp/nfp_net_offload.c |  3 +++
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_bpf.h b/drivers/net/ethernet/netronome/nfp/nfp_bpf.h
index fc220cd04115..87aa8a3e9112 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_bpf.h
+++ b/drivers/net/ethernet/netronome/nfp/nfp_bpf.h
@@ -192,20 +192,10 @@ struct nfp_bpf_result {
 	bool dense_mode;
 };
 
-#ifdef CONFIG_BPF_SYSCALL
 int
 nfp_bpf_jit(struct bpf_prog *filter, void *prog, enum nfp_bpf_action_type act,
 	    unsigned int prog_start, unsigned int prog_done,
 	    unsigned int prog_sz, struct nfp_bpf_result *res);
-#else
-int
-nfp_bpf_jit(struct bpf_prog *filter, void *prog, enum nfp_bpf_action_type act,
-	    unsigned int prog_start, unsigned int prog_done,
-	    unsigned int prog_sz, struct nfp_bpf_result *res)
-{
-	return -ENOTSUPP;
-}
-#endif
 
 int nfp_prog_verify(struct nfp_prog *nfp_prog, struct bpf_prog *prog);
 
diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_offload.c b/drivers/net/ethernet/netronome/nfp/nfp_net_offload.c
index 43f42f842eda..8acfb631a0ea 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_offload.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_offload.c
@@ -148,6 +148,9 @@ nfp_net_bpf_offload_prepare(struct nfp_net *nn,
 	unsigned int max_mtu;
 	int ret;
 
+	if (!IS_ENABLED(CONFIG_BPF_SYSCALL))
+		return -ENOTSUPP;
+
 	ret = nfp_net_bpf_get_act(nn, cls_bpf);
 	if (ret < 0)
 		return ret;
-- 
2.9.0

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#1490926

On Fri, 23 Sep 2016 22:23:59 +0200, Arnd Bergmann wrote:
> I stumbled over a new warning during randconfig testing,
> with CONFIG_BPF_SYSCALL disabled:
> 
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c: In function 'nfp_net_bpf_offload':
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: '*((void *)&res+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: 'res.n_instr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> As far as I can tell, this is a false positive caused by the compiler
> getting confused about a function that is partially inlined, but it's
> easy to avoid while improving the code:
> 
> The nfp_bpf_jit() stub helper for that configuration is unusual as it
> is defined in a header file but not marked 'static inline'. By moving
> the compile-time check into the caller using the IS_ENABLED() macro,
> we can remove that stub and simplify the nfp_net_bpf_offload_prepare()
> function enough to unconfuse the compiler.
> 
> Fixes: 7533fdc0f77f ("nfp: bpf: add hardware bpf offload")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks Arnd!  static inline definitely missing there but if we can
depend on dead code elimination to remove the symbol that's even cooler!

Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>

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#1491088

From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 23 Sep 2016 22:23:59 +0200

> I stumbled over a new warning during randconfig testing,
> with CONFIG_BPF_SYSCALL disabled:
> 
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c: In function 'nfp_net_bpf_offload':
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: '*((void *)&res+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> drivers/net/ethernet/netronome/nfp/nfp_net_offload.c:263:3: error: 'res.n_instr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> As far as I can tell, this is a false positive caused by the compiler
> getting confused about a function that is partially inlined, but it's
> easy to avoid while improving the code:
> 
> The nfp_bpf_jit() stub helper for that configuration is unusual as it
> is defined in a header file but not marked 'static inline'. By moving
> the compile-time check into the caller using the IS_ENABLED() macro,
> we can remove that stub and simplify the nfp_net_bpf_offload_prepare()
> function enough to unconfuse the compiler.
> 
> Fixes: 7533fdc0f77f ("nfp: bpf: add hardware bpf offload")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Applied, thanks.

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