On Tue, Sep 22, 2009 at 1:09 AM, Vitaliy Margolen <wine-de...@kievinfo.com> wrote: > Ben Klein wrote: >> The question remains, how exactly does >> FIELD_OFFSET work, and does it end up dereferencing ca[5]? > It does pointer arithmetic and does not dereference anything. "ca[5]" is the > same as "(ca + 5)" or on lower level "((char*)ca + 5*sizeof(ca[0]))" and > does not require any dereferencing.
It does, since field offset macro takes the easy approach: #define FIELD_OFFSET(type, field) ((LONG)(INT_PTR)&(((type *)0)->field)) which basically dereferences a null pointer to get the offset. This would be a bug in cppcheck since we don't actually dereference ca[5]. Moreover, since cppcheck doesn't catch the similar FIELD_OFFSET uses as bugs, it seems that it is mistaking ca[5] for the local ca, as opposed to the cs_t->ca. > >> [/home/cahrendt/wine-git/dlls/wineps.drv/init.c:270]: (error) Possible >> null pointer dereference: dmW - otherwise it is redundant to check if >> dmW is null at line 272 > > This is a real bug and should be fixed: >> ptrdiff_t off_formname = (const char *)dmW->dmFormName - (const char >> *)dmW; > Does indeed dereference dmW to get the value of dmFormName. It actually doesn't, it's a tricky case where dmW->dwFormName == &dmW->dwFormName, because dwFormName is an array allocated as part of the struct. I made that mistake too the previous cppcheck round. > > Vitaliy. > Mike.
