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Re: [PATCH] hw/net/i82596: Correct command bitmask (CID 1419392)


From: Peter Maydell
Subject: Re: [PATCH] hw/net/i82596: Correct command bitmask (CID 1419392)
Date: Fri, 13 Mar 2020 11:01:48 +0000

On Fri, 14 Feb 2020 at 00:48, Philippe Mathieu-Daudé <address@hidden> wrote:
>
> The command is 32-bit, but we are loading the 16 upper bits with
> the 'get_uint16(s->scb + 2)' call.
>
> Once shifted by 16, the command bits match the status bits:
>
> - Command
>   Bit 31 ACK-CX   Acknowledges that the CU completed an Action Command.
>   Bit 30 ACK-FR   Acknowledges that the RU received a frame.
>   Bit 29 ACK-CNA  Acknowledges that the Command Unit became not active.
>   Bit 28 ACK-RNR  Acknowledges that the Receive Unit became not ready.
>
> - Status
>   Bit 15 CX       The CU finished executing a command with its I(interrupt) 
> bit set.
>   Bit 14 FR       The RU finished receiving a frame.
>   Bit 13 CNA      The Command Unit left the Active state.
>   Bit 12 RNR      The Receive Unit left the Ready state.
>
> Add the SCB_COMMAND_ACK_MASK definition to simplify the code.
>
> This fixes Coverity 1419392 (CONSTANT_EXPRESSION_RESULT):
>
>   /hw/net/i82596.c: 352 in examine_scb()
>   346         cuc = (command >> 8) & 0x7;
>   347         ruc = (command >> 4) & 0x7;
>   348         DBG(printf("MAIN COMMAND %04x  cuc %02x ruc %02x\n", command, 
> cuc, ruc));
>   349         /* and clear the scb command word */
>   350         set_uint16(s->scb + 2, 0);
>   351
>   >>>     CID 1419392:    (CONSTANT_EXPRESSION_RESULT)
>   >>>     "command & (2147483648UL /* 1UL << 31 */)" is always 0 regardless 
> of the values of its operands. This occurs as the logical operand of "if".
>   352         if (command & BIT(31))      /* ACK-CX */
>   353             s->scb_status &= ~SCB_STATUS_CX;
>   >>>     CID 1419392:    (CONSTANT_EXPRESSION_RESULT)
>   >>>     "command & (1073741824UL /* 1UL << 30 */)" is always 0 regardless 
> of the values of its operands. This occurs as the logical operand of "if".
>   354         if (command & BIT(30))      /*ACK-FR */
>   355             s->scb_status &= ~SCB_STATUS_FR;
>   >>>     CID 1419392:    (CONSTANT_EXPRESSION_RESULT)
>   >>>     "command & (536870912UL /* 1UL << 29 */)" is always 0 regardless of 
> the values of its operands. This occurs as the logical operand of "if".
>   356         if (command & BIT(29))      /*ACK-CNA */
>   357             s->scb_status &= ~SCB_STATUS_CNA;
>   >>>     CID 1419392:    (CONSTANT_EXPRESSION_RESULT)
>   >>>     "command & (268435456UL /* 1UL << 28 */)" is always 0 regardless of 
> the values of its operands. This occurs as the logical operand of "if".
>   358         if (command & BIT(28))      /*ACK-RNR */
>   359             s->scb_status &= ~SCB_STATUS_RNR;
>
> Fixes: Covertiy CID 1419392 (commit 376b851909)

("Coverity")

> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>

Reviewed-by: Peter Maydell <address@hidden>

Jason, are you planning to pick this one up?

thanks
-- PMM



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