Re: [xml] GCC 10 analyzer findings

[Nick Wellnhofer <wellnhofer aevum de>]

On 16/07/2020 11:49, Jeffrey Walton via xml wrote:
> I'm building libxml2-2.9.10 on Fedora 32 with GCC 10. GCC 10 includes
> the analyzer. The analyzer can be enabled by adding -fanalyze to
> CFLAGS and LDFLAGS.
>
> The analyzer is producing some use-after-free and double-free findings
> on libxml2-2.9.10.

I gave it a try and here are my observations:

xmlMalloc and similar entry points are function pointers. To make the static 
analyzer understand that these are actually malloc calls, we need a special 
configuration where xmlMalloc is defined as a macro or function.

libxml2 typically zeroes freshly allocated memory with memset and assumes this 
initializes pointers with NULL. Although I haven't seen a platform where this 
doesn't work, the C standard makes no such guarantee. To avoid false 
positives, such pointers must be initialized in a different way.

There are quite a few bug reports about false positives with GCC's analyzer in 
the initial release, so I'd wait for a newer release before giving it another 
look.

Nick