Avoiding _memset?
in [Visual C]
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From: xiaosi on 9 Sep 2009 05:07 It's strange that why to use loop instead of __stosb on none _M_AMD64 cpu. On my AMD32 cpu, __stosb (114 clocks) is faster than this loop (195 clocks). FORCEINLINE PVOID RtlSecureZeroMemory( __in_bcount(cnt) PVOID ptr, __in SIZE_T cnt ) { volatile char *vptr = (volatile char *)ptr; #if defined(_M_AMD64) __stosb((PBYTE )((DWORD64)vptr), 0, cnt); #else while (cnt) { *vptr = 0; vptr++; cnt--; } #endif return ptr; } "Alex Blekhman" <tkfx.REMOVE(a)yahoo.com> wrote: > I found in the WinNT.h header the SecureZeroMemory macro, which > expands to the RtlSecureZeroMemory function. It is implemented > inline in the header file, so it doesn't have any external > dependencies. Basically, it's a straightforward implementation of > memset. > > HTH > Alex
From: Vincent Fatica on 9 Sep 2009 10:00 On Wed, 9 Sep 2009 15:25:55 +0800, "xiaosi" <xiaosi(a)cn99.com> wrote: |When add /FORCE:MULTIPLE to linker option: |LIBCMT.lib(_wctype.obj) : warning LNK4006: _iswlower already defined in ntdll.lib(ntdll.dll); second definition ignored |LIBCMT.lib(_wctype.obj) : warning LNK4006: _iswdigit already defined in ntdll.lib(ntdll.dll); second definition ignored Yes, I discovered that and tried it. It worked but the resulting scary warnings made it seem rather heavy-handed. I read about the purpose of ntdll.dll (as an interface to the native API). Then I looked at the win7 version of ntdll.lib in the WDK. It contains *none* of the CTR stuff (str*, wcs*, ...) that's in the winxp version. Do you suppose it's incomplete ... or perhaps, has the philosophy changed? -- - Vince
From: Vincent Fatica on 9 Sep 2009 10:12 On Wed, 9 Sep 2009 10:48:28 +0300, "Alex Blekhman" <tkfx.REMOVE(a)yahoo.com> wrote: |"Vincent Fatica" wrote: |> |You can use the ZeroMemory macro, which results in a call to |> ntdll.dll's RtlZeroMemory routine instead of pulling in the CRT. |> |> Tried that ... results in a call to _memset. | |I found in the WinNT.h header the SecureZeroMemory macro, which |expands to the RtlSecureZeroMemory function. It is implemented |inline in the header file, so it doesn't have any external |dependencies. Basically, it's a straightforward implementation of |memset. Yes, I discovered that early on. It works, using 7 bytes more text than stosd (if I recall correctly). -- - Vince
From: Vincent Fatica on 9 Sep 2009 10:12 On Wed, 9 Sep 2009 17:07:18 +0800, "xiaosi" <xiaosi(a)cn99.com> wrote: |It's strange that why to use loop instead of __stosb on none _M_AMD64 cpu. |On my AMD32 cpu, __stosb (114 clocks) is faster than this loop (195 clocks). How do you time such things? -- - Vince
From: xiaosi on 9 Sep 2009 10:19
Those crt functions in ntdll.dll seems to be undocumented feature of Windows. I had never heard of this before the day that I "dumpbined" it. Since it's undocumented, Windows does not promise to support this in the future. "Vincent Fatica" <vince(a)blackholespam.net> wrote: > On Wed, 9 Sep 2009 15:25:55 +0800, "xiaosi" <xiaosi(a)cn99.com> wrote: > > |When add /FORCE:MULTIPLE to linker option: > |LIBCMT.lib(_wctype.obj) : warning LNK4006: _iswlower already defined in ntdll.lib(ntdll.dll); second definition ignored > |LIBCMT.lib(_wctype.obj) : warning LNK4006: _iswdigit already defined in ntdll.lib(ntdll.dll); second definition ignored > > Yes, I discovered that and tried it. It worked but the resulting scary warnings > made it seem rather heavy-handed. > > I read about the purpose of ntdll.dll (as an interface to the native API). Then > I looked at the win7 version of ntdll.lib in the WDK. It contains *none* of the > CTR stuff (str*, wcs*, ...) that's in the winxp version. Do you suppose it's > incomplete ... or perhaps, has the philosophy changed? > -- > - Vince |