netdev - Re: [PATCH net-next 3/3] eth: bnxt: handle invalid Tx completions more gracefully

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Message-ID: <20230711181919.50f27180@kernel.org>
Date: Tue, 11 Jul 2023 18:19:19 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 michael.chan@...adcom.com
Subject: Re: [PATCH net-next 3/3] eth: bnxt: handle invalid Tx completions
 more gracefully

On Tue, 11 Jul 2023 12:10:28 +0200 Paolo Abeni wrote:
> On Mon, 2023-07-10 at 13:56 -0700, Jakub Kicinski wrote:
> > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.h b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > index 080e73496066..08ce9046bfd2 100644
> > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > @@ -1008,6 +1008,7 @@ struct bnxt_napi {
> >  					  int);
> >  	int			tx_pkts;
> >  	u8			events;
> > +	u8			tx_fault:1;  
> 
> Since there are still a few holes avail, I would use a plain u8 (or
> bool) to help the compiler emit better code.

Is that still true or was it only true for old compilers?
With gcc version 13.1.1 20230614 :

$ cat /tmp/t.c 
#include <strings.h>

struct some {
    void (*f)(void);
    unsigned char b;
#ifdef BLA
    _Bool a;
#else
    unsigned char a:1;
#endif
};

int bla(struct some *s)
{
    if (s->a)
        s->f();
    return 0;
}

$ gcc -W -Wall -O2  /tmp/t.c -o /tmp/t -c
$ objdump -S /tmp/t > /tmp/a
$ gcc -DBLA -W -Wall -O2  /tmp/t.c -o /tmp/t -c
$ objdump -S /tmp/t > /tmp/b
$ diff /tmp/a /tmp/b
8c8
<    0:	f6 47 09 01          	testb  $0x1,0x9(%rdi)
---
>    0:	80 7f 09 00          	cmpb   $0x0,0x9(%rdi)

$ gcc -V

Shouldn't matter, right?