Re: gdb 8.0 "lazy_string" exception "Length is larger than array size"

[Phil Muldoon <pmuldoon at redhat dot com>]

On 25/09/17 18:20, Michael Stahl wrote:
> 
> hi,
> 
> for the following string type:
> 
>   /** The implementation of a Unicode string.
>   */
>   typedef struct SAL_DLLPUBLIC_RTTI _rtl_uString
>   {
>       oslInterlockedCount refCount; /* opaque */
>       sal_Int32           length;
>       sal_Unicode         buffer[1];
>   } rtl_uString;
> 
> the gdb python pretty-printer calls:
> 
> 	return data.lazy_string(encoding, length)
> 
> full python pretty-printer module:
> 
> https://gerrit.libreoffice.org/gitweb?p=core.git;a=blob;f=solenv/gdb/libreoffice/util/string.py;h=32583718f83b2ad5707f75dd6327d9aa62764439;hb=5f210715fe090b4db4c80dcdee5f77dc404cf85c#l56
> 
> now this results in this exception:
> 
>   Traceback (most recent call last):
>     File "/work/lo/master/solenv/gdb/libreoffice/util/string.py", line
> 29, in to_string
>       return self.make_string(data, self.encoding, len)
>     File "/work/lo/master/solenv/gdb/libreoffice/util/string.py", line
> 66, in make_string
>       return data.lazy_string(encoding, length)
>   gdb.error: Length is larger than array size.
> 
> this is with Fedora 26 "GNU gdb (GDB) Fedora 8.0.1-26.fc26" - in Fedora
> 25 this did not throw an exception.
> 
> apparently the problem is that the array is statically declared as
> "buffer[1]", however its actual dynamic size is the same as "length".
> 
> is this a bug in gdb or is lazy_string not intended to support this
> scenario?
> 
> regards,
>  michael
> 

Yeah, it's determining the string is an array and finding that the
declared length is larger then the array size. This is (as you noted)
the initial length of the array is [1] and that array is then
modified later. This code was added at 34b433203b5 by Doug Evans and
it was noted it was a bug. I've not sure, though, fixing this bug
may have had unintended consequences. I've CC'd Doug on the patch
and maybe he could comment further.

Cheers

Phil