linux-kernel - Re: [PATCH] amdgpu: fix gcc -Wrestrict warning

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Date:   Wed, 24 Mar 2021 14:33:30 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Huang Rui <ray.huang@....com>,
        Jinzhou Su <Jinzhou.Su@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] amdgpu: fix gcc -Wrestrict warning

On Tue, Mar 23, 2021 at 4:57 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> On 23/03/2021 14.04, Arnd Bergmann wrote:
> >                       if (securedisplay_cmd->status == TA_SECUREDISPLAY_STATUS__SUCCESS) {
> > +                             int pos = 0;
> >                               memset(i2c_output,  0, sizeof(i2c_output));
> >                               for (i = 0; i < TA_SECUREDISPLAY_I2C_BUFFER_SIZE; i++)
> > -                                     sprintf(i2c_output, "%s 0x%X", i2c_output,
> > +                                     pos += sprintf(i2c_output + pos, " 0x%X",
> >                                               securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
> >                               dev_info(adev->dev, "SECUREDISPLAY: I2C buffer out put is :%s\n", i2c_output);
>
> Eh, why not get rid of the 256 byte stack allocation and just replace
> all of this by
>
>   dev_info(adev->dev, ""SECUREDISPLAY: I2C buffer out put is: %*ph\n",
> TA_SECUREDISPLAY_I2C_BUFFER_SIZE,
> securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf);
>
> That's much less code (both in #LOC and .text), and avoids adding yet
> another place that will be audited over and over for "hm, yeah, that
> sprintf() is actually not gonna overflow".
>
> Yeah, it'll lose the 0x prefixes for each byte and use lowercase hex chars.

Ah, I didn't know the kernel's sprintf could do that, that's really nice.

I'll send a follow-up patch, as Alex has already applied the first one.

Alex, feel free to merge the two into one, or just keep as they are.

      Arnd