[systemd-devel] [PATCH] fix strict aliasing violations in src/udev/udev-builtin-usb_id.c

[Shawn Landden]

Oh wait, I c, yes I had same question.

On Wed, Mar 4, 2015 at 8:07 PM, Shawn Landden <shawn at churchofgit.com> wrote:

> On Wed, Mar 4, 2015 at 7:58 PM, Zbigniew Jędrzejewski-Szmek <
> zbyszek at in.waw.pl> wrote:
>
>> On Tue, Mar 03, 2015 at 04:21:30PM -0800, Shawn Landden wrote:
>> > also switch to <inttypes.h>
>> > ---
>> >  src/udev/udev-builtin-usb_id.c | 35 ++++++++++++++++++-----------------
>> >  1 file changed, 18 insertions(+), 17 deletions(-)
>> >
>> > diff --git a/src/udev/udev-builtin-usb_id.c
>> b/src/udev/udev-builtin-usb_id.c
>> > index ab0d96e..0223421 100644
>> > --- a/src/udev/udev-builtin-usb_id.c
>> > +++ b/src/udev/udev-builtin-usb_id.c
>> > @@ -28,6 +28,7 @@
>> >  #include <ctype.h>
>> >  #include <fcntl.h>
>> >  #include <errno.h>
>> > +#include <inttypes.h>
>> >
>> >  #include "udev.h"
>> >
>> > @@ -153,15 +154,15 @@ static int dev_if_packed_info(struct udev_device
>> *dev, char *ifs_str, size_t len
>> >          int pos = 0;
>> >          unsigned strpos = 0;
>> >          struct usb_interface_descriptor {
>> > -                u_int8_t        bLength;
>> > -                u_int8_t        bDescriptorType;
>> > -                u_int8_t        bInterfaceNumber;
>> > -                u_int8_t        bAlternateSetting;
>> > -                u_int8_t        bNumEndpoints;
>> > -                u_int8_t        bInterfaceClass;
>> > -                u_int8_t        bInterfaceSubClass;
>> > -                u_int8_t        bInterfaceProtocol;
>> > -                u_int8_t        iInterface;
>> > +                uint8_t        bLength;
>> > +                uint8_t        bDescriptorType;
>> > +                uint8_t        bInterfaceNumber;
>> > +                uint8_t        bAlternateSetting;
>> > +                uint8_t        bNumEndpoints;
>> > +                uint8_t        bInterfaceClass;
>> > +                uint8_t        bInterfaceSubClass;
>> > +                uint8_t        bInterfaceProtocol;
>> > +                uint8_t        iInterface;
>> >          } __attribute__((packed));
>> >
>> >          if (asprintf(&filename, "%s/descriptors",
>> udev_device_get_syspath(dev)) < 0)
>> > @@ -179,21 +180,21 @@ static int dev_if_packed_info(struct udev_device
>> *dev, char *ifs_str, size_t len
>> >
>> >          ifs_str[0] = '\0';
>> >          while (pos < size && strpos+7 < len-2) {
>> > -                struct usb_interface_descriptor *desc;
>> > +                struct usb_interface_descriptor desc;
>> >                  char if_str[8];
>> >
>> > -                desc = (struct usb_interface_descriptor *) &buf[pos];
>> > -                if (desc->bLength < 3)
>> > +                memcpy(&desc, &buf[pos], sizeof(desc));
>> Copying it seems suboptimal. But is this actually an aliasing
>> violation? buf is a char array, and [1] says: "a character type
>> may alias any other type".
>>
>> Common misunderstanding about strict aliasing. if accessing as char *
> yes, but not the other way around. See the C11 standard which makes it
> clear (don't have page number off the top of my head...)
>
>> [1]
>> https://gcc.gnu.org/onlinedocs/gcc-4.6.1/gcc/Optimize-Options.html#index-fstrict_002daliasing-825
>>
>> Zbyszek
>> _______________________________________________
>> systemd-devel mailing list
>> systemd-devel at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/systemd-devel
>>
>
>
>
> --
> Shawn Landden
>



-- 
Shawn Landden
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