[LITMUS^RT] Error Compiling liblitmus

[Mahircan Gül]

Hi everyone

The issues mentioned by Manohar are fixed with the latest patch:
https://github.com/LITMUS-RT/liblitmus/commit/cf1d1f6e4b1138a5a841a47a2cba4aacdcaf0d72

/liblitmus/ should now be compiled without gcc's array-bounds warning.


Thanks
Mahir

On 07/15/2016 12:47 PM, Manohar Vanga wrote:
>
>
> On Fri, Jul 15, 2016 at 10:56 AM, Björn Brandenburg <bbb at mpi-sws.org 
> <mailto:bbb at mpi-sws.org>> wrote:
>
>
>     > On 15 Jul 2016, at 01:49, Roohollah
>     <roohollahamiri at u.boisestate.edu
>     <mailto:roohollahamiri at u.boisestate.edu>> wrote:
>     >
>     > I am trying to compile liblitmus, the latest version. But I am
>     getting the following error:
>     >
>     > src/migration.c:83:27: error: array subscript is below array
>     bounds [-Werror=array-bounds]
>     >
>     > I am using Fedora 24, gcc-6.1.1 . Is there any one know how to
>     solve that problem?
>
>
>     Looks like there’s an out-of-bounds access in Glenn’s domain
>     parsing code.
>
>     https://github.com/LITMUS-RT/liblitmus/blob/master/src/migration.c#L83
>
>     However, Mahir recently patched that loop and changed one of the
>     indices. Perhaps the patch was incomplete?
>
>     https://github.com/LITMUS-RT/liblitmus/commit/322eaadaa95b4f64f4102a9bc6aaa2237401ae41
>
>     Mahir, can you please look into this?
>
>
> The change is incorrect. It should be 8 because the last chunk doesn't 
> have a trailing comma. Consider the following example:
>
> buf="xxx,xxxxxxxx,xxxxxxxx"
> We want to parse it backwards starting with the last 8 characters.
> At line 67, "chunk_str = buf + len - 8" gives the correct behavior 
> (chunk_str = "xxxxxxxx").
> "chunk_str = buf + len - 9" ends up giving (chunk_str = ",xxxxxxxx").
>
> On the other hand, the exit condition in the do-while loop is relying 
> on out-of-bounds pointer arithmetic which is undefined in the C 
> standard. I'm guessing the warning is something that was recently 
> introduced in GCC.
>
> The loop can just be rewritten as follows to avoid the use of 
> undefined behaviour (I leave the correct patching to Mahir). Hopefully 
> this removes the issue:
>
>     /* process LSB chunks first (at the end of the str) and move 
> backward */
>     chunk_str = buf + len;
>     i = 0;
>     do
>     {
>         unsigned long chunk;
>         chunk_str -= 9;
>         if(chunk_str < buf)
>             chunk_str = buf; /* when MSB mask is less than 8 chars */
>         chunk = strtoul(chunk_str, NULL, 16);
>         while (chunk) {
>             int j = ffsl(chunk) - 1;
>             int x = i*32 + j;
>             CPU_SET_S(x, *sz, *set);
>             chunk &= ~(1ul << j);
>         }
>         i += 1;
>     } while(chunk_str > buf);
>
> (Please do review this carefully though.) Thanks!

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