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bug#24874: dd: misleading parsing of hex numbers
From: |
Pádraig Brady |
Subject: |
bug#24874: dd: misleading parsing of hex numbers |
Date: |
Fri, 4 Nov 2016 17:03:29 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
On 04/11/16 16:20, Pádraig Brady wrote:
> On 04/11/16 11:19, Stephan Bauroth wrote:
>> Dear coreutils team :)
>>
>> I encountered a buglike behaviour of dd when handling skip and count
>> parameters that are encoded in hex and thus prefixed with 0x.
>>
>> dd is not able to parse them, which is OK but would be great if it would
>> be, but, worse, reads 0xf00 as 0. It does that silently. While an
>> enduser will immediately notice this on count, since nothing is copied,
>> behaviour for skip looks ok. (In fact, I noticed this only because I
>> hexdumped the result after hours of debugging)
>>
>> While it's OK that dd can't parse these numbers, maybe there should be a
>> warning that 0x was found and interpreted as 0. Since a char like 'x' is
>> invalid within a number that by definition has to be decimal, a warning
>> should be fairly easy to implement.
>>
>> Of course, the ability to parse hex numbers in these parameters would be
>> awesome :)
>>
>> regards and thanks for your continuing work,
>> Stephan Bauroth
>
> Ouch. That's a real gotcha.
> Note hex digits after the 0x are diagnosed, but not decimal digits:
>
> $ dd skip=0x100 seek=0xf00
> dd: invalid number: ‘0xf00’
>
> Disallowing 0x... could definitely break backwards compat though.
> Consider `for rec in 0 1 2; do dd skip=${rec}x1024...`
>
> I suppose we could output a warning to suggest using
> $(($rec * $size)) or 0${rec}x${size}
> if that really is the intention?
>
> Given the warning workaround would be suggested in the message,
> and that it's a relatively rare usage, a warning is probably appropriate here.
> We already warn in dd for various usage.
>
> I'll fix that for the coming release.
Patch attached.
dd-0x-warn.patch
Description: Text Data