Messages in this thread | | | Date | Mon, 27 Jan 2014 09:34:34 +0800 | From | Ren Qiaowei <> | Subject | Re: [PATCH v3 4/4] x86, mpx: extend siginfo structure to include bound violation information |
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On 01/27/2014 05:38 AM, David Rientjes wrote: > On Sun, 26 Jan 2014, Ren Qiaowei wrote: > >>> arch/x86/kernel/mpx.c: In function ‘do_mpx_bounds’: >>> arch/x86/kernel/mpx.c:407:3: warning: cast to pointer from integer of >>> different size [-Wint-to-pointer-cast] >>> arch/x86/kernel/mpx.c:409:3: warning: cast to pointer from integer of >>> different size [-Wint-to-pointer-cast] >>> >>> and the documentation says you explicitly want to support this config. >>> >>> These types of warnings are usually indicative of real problems when >>> you're storing upper and lower bits in 32-bit fields after casting them >>> from 64-bit values. >>> >>> I'm also not sure if the added fields to the generic struct siginfo can be >>> justified for this. >>> >> According to MPX spec, for 32-bit case, the upper 32-bits of 64-bits bound >> register are ignored, and so casting to pointer from 64-bit values should be >> not produce any problems. >> > > Ok, so this is intended per the spec which nobody reading the code is > going to know and people who report the compile warnings are going to > continue to question it. > > How are you planning on suppressing the warnings? It will probably > require either > > - separate 64-bit and 32-bit helper functions to do_mpx_bounds() to > do appropriate casts before casting to a pointer, or > > - a macro defined as a no-op for 64-bit and as a cast to 32-bit value > for 32-bit configs that will be used in do_mpx_bounds() and casted > to the pointer. > I agree with you and we should suppress all the warnings as possible. If I use (unsgined long) to cast like the following code, what do you think about it? sizeof(long) will be 4 for 32-bit.
info->si_lower = (void __user *)(unsigned long) (xsave_buf->bndregs.bndregs[2*bndregno]); info->si_upper = (void __user *)(unsigned long) (~xsave_buf->bndregs.bndregs[2*bndregno+1]);
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