Re: 'struct dynamic': struct tag leak in UAPI headers

[Alejandro Colomar <alx@kernel.org>]

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Hi Matthew,

On 2023-08-29 14:24, Matthew Wilcox wrote:
> On Tue, Aug 29, 2023 at 02:08:45PM +0200, Alejandro Colomar wrote:
>> It seems we should blame an automated script :)
>>
>> $ git blame -- ./include/uapi/linux/elf.h | grep 'struct dynamic';
>> 23a7aea5faf65 (Rolf Eike Beer        2022-10-04 12:25:40 +0200 143) typedef struct dynamic {
>>
>> $ git blame 23a7aea5faf65^ -- ./include/uapi/linux/elf.h | grep 'struct dynamic';
>> 607ca46e97a1b (David Howells         2012-10-13 10:46:48 +0100 143) typedef struct dynamic{
>>
>> $ git log -1 607ca46e97a1b
>> commit 607ca46e97a1b6594b29647d98a32d545c24bdff
>> Author: David Howells <dhowells@redhat.com>
>> Date:   Sat Oct 13 10:46:48 2012 +0100
>>
>>     UAPI: (Scripted) Disintegrate include/linux
> 
> Sure, but that didn't introduce it, it just moved it.
> 
> It was introduced before git, so trawling through linux-fullhistory ....


diff --git a/include/linux/elf.h b/include/linux/elf.h
-typedef struct dynamic{
--
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
+typedef struct dynamic{


Hmm, I thought that commit was the one that moved it from an internal header
to a UAPI one.  I didn't know include/linux/elf.h was a public header long ago.

> 
> Linux 1.1.54:
> 
> -struct dynamic{
> +typedef struct dynamic{
>    int d_tag;
>    union{
>      int d_val;
>      char * d_ptr;
>    } d_un;
> -};
> +} Elf32_Dyn;
> 
> Before that, 0.99.13 added linux/elf.h and it included:
> 
> +struct dynamic{
> +  int d_tag;
> +  union{
> +    int d_val;
> +    char * d_ptr;
> +  } d_un;
> +};
> 
> So anybody who's included linux/elf.h since 1993 has had this definition,
> and maybe the risk of breaking something is greater than the desire to
> allow new code to use 'struct dynamic'?

Might be true.  But since it's a compile-time failure, it's not going to
cause silent bugs.  If there was a real regression, it would be trivial to
detect and fix, so maybe it's a risk that can be taken.  But yeah, your
concern may vary.  :)

Cheers,
Alex

-- 
<http://www.alejandro-colomar.es/>
GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5


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