Re: [Tinycc-devel] -fsanitizer=address

[Michael Matz]

Hello Pascal,

On Thu, 13 Jun 2019, Pascal Cuoq wrote:

> This appears to be caused by an offset into a dynamically allocated block
> being assigned to sym in build_got_entries at line 1041:
>
>             sym = &((ElfW(Sym) *)symtab_section->data)[sym_index];
>
> And this dynamically allocated block being realloc'ed as a result of calling
> build_got(s1) at line 1102:
>
>                 build_got(s1);
>
> Bearing in mind that we keep using sym at line 1108:
>
>             attr = put_got_entry(s1, reloc_type, sym->st_size, sym->st_info,
>                                  sym_index);
>
> I have no idea what I am doing, but I applied the following patch and it
> seems to have fixed the dangling pointer, according to the tool I use (not
> ASan).

The analysis and fix are correct.  But there's an even better way, the 
usage of sym is useless there, the function put_got_entry is recomputing
sym already anyway, so there's no need to pass stuff into it that's 
readily available in a different way, removing two paramters and the 
problematic use.  That's what is in mob now.


Ciao,
Michael.