[PATCH] nscd_stat.c: make the build reproducible

[Ximin Luo]

Mike Frysinger:
> On 28 Jul 2016 15:15, Florian Weimer wrote:
>> On 03/09/2016 05:30 PM, Mike Frysinger wrote:
>>> would it be so terrible to properly marshall this data ?
>>
>> Ximin Luo and I discussed this and I wonder if it is possible to read 
>> out the libc.so.6 build ID if it is present.  It should indirectly call 
>> all the layout dependencies and be reasonably easy to access because it 
>> is in an allocated section (and we might want to print it from an 
>> libc.so.6 invocation, too).
>>
>> We still need the time-based approach if the build ID is not available, 
>> but I expect most distributions will have something like it.
>>
>> The Debian bug is:
>>
>>    https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=783210
>>
>> (Also Cc:ed)
> 
> agreed that build-id should be an acceptable replacement for what the
> code is doing today, but in order to pull that off, i guess you'd have
> to have to do a configure test to see if build-id is active ?  if you
> leave the logic to runtime, you'd still need to include the datetime
> stamp in the object which would still make the build unreproducible.
> 
> this also doesn't really cover the quoted idea of marshalling the data
> between client & server :).
> -mike
> 

Hi all,

I've written a small program that prints out the Build IDs of all the objects that are dynamically linked to it, plus itself.

It works well, although I'm not a C expert so I don't know if it is portable enough. For example, I hard-code some >>2 <<2s in there, along with a uint8_t - I didn't see a corresponding ElfW(xxx) type in elf.h

Another downside is it needs to be linked against libdl, which I think is not the case currently with nscd. I'm not sure if this carries extra security risk or whatever.

An alternative would be to detect the build-id *at build time* and then monkey-patch it into the binary itself.

What do you all think? How shall I proceed?

X

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