Avoiding _memset?
in [Visual C]
|
From: Ben Voigt [C++ MVP] on 8 Sep 2009 16:01 "Vincent Fatica" <vince(a)blackholespam.net> wrote in message news:4aa3de92$1(a)news.vefatica.net... > (VC9) I am trying to avoid the runtime library in a tiny app (something I > do > regularly). When I try to zero-fill a STARTUPINFO struct with a for-loop, > the > compiler turns my for-loop into a call to _memset. > > ; 13 : STARTUPINFO si; > ; 14 : si.cb = sizeof(si); > ; 15 : for (BYTE *p = (BYTE*) &si + sizeof(si.cb); p < (BYTE*) &si + > sizeof(si); p++) > ; 16 : *p=0; > > push 64 ; 00000040H > lea edx, DWORD PTR _si$[esp+104] > push 0 > push edx > add esi, 2 > mov DWORD PTR _si$[esp+108], 68 ; 00000044H > call _memset > add esp, 12 ; 0000000cH > > How do I avoid that (elegantly)? Is it some kind of optimization I can > simply > turn off? I can trick the compiler with the likes of > > ; 16 : *p = p ? 0 : 1; // in the loop > > That avoids the _memset, but seems particularly kludgy. You can use the ZeroMemory macro, which results in a call to ntdll.dll's RtlZeroMemory routine instead of pulling in the CRT. > > Thanks. > -- > - Vince
From: Vincent Fatica on 8 Sep 2009 16:13 On Tue, 8 Sep 2009 15:01:40 -0500, "Ben Voigt [C++ MVP]" <bvoigt(a)newsgroup.nospam> wrote: | | |"Vincent Fatica" <vince(a)blackholespam.net> wrote in message |news:4aa3de92$1(a)news.vefatica.net... |> (VC9) I am trying to avoid the runtime library in a tiny app (something I |> do |> regularly). When I try to zero-fill a STARTUPINFO struct with a for-loop, |> the |> compiler turns my for-loop into a call to _memset. |> |> ; 13 : STARTUPINFO si; |> ; 14 : si.cb = sizeof(si); |> ; 15 : for (BYTE *p = (BYTE*) &si + sizeof(si.cb); p < (BYTE*) &si + |> sizeof(si); p++) |> ; 16 : *p=0; |> |> push 64 ; 00000040H |> lea edx, DWORD PTR _si$[esp+104] |> push 0 |> push edx |> add esi, 2 |> mov DWORD PTR _si$[esp+108], 68 ; 00000044H |> call _memset |> add esp, 12 ; 0000000cH |> |> How do I avoid that (elegantly)? Is it some kind of optimization I can |> simply |> turn off? I can trick the compiler with the likes of |> |> ; 16 : *p = p ? 0 : 1; // in the loop |> |> That avoids the _memset, but seems particularly kludgy. | |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. -- - Vince
From: Giovanni Dicanio on 8 Sep 2009 18:41 Vincent Fatica ha scritto: > |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. In WinNT.h I read: #define RtlZeroMemory(Destination,Length) memset((Destination),0,(Length)) Giovanni
From: Ben Voigt [C++ MVP] on 8 Sep 2009 19:22 "Giovanni Dicanio" <giovanniDOTdicanio(a)REMOVEMEgmail.com> wrote in message news:erxaMWNMKHA.4124(a)TK2MSFTNGP04.phx.gbl... > Vincent Fatica ha scritto: > >> |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. > > In WinNT.h I read: > > #define RtlZeroMemory(Destination,Length) memset((Destination),0,(Length)) Yes, but I think there is a real exported function in ntdll.dll So maybe RtlZeroMemory needs to be #undef-d > > > Giovanni > >
From: Vincent Fatica on 8 Sep 2009 19:44
On Tue, 8 Sep 2009 13:32:29 +0800, "xiaosi" <xiaosi(a)cn99.com> wrote: |in ntdll.dll. | | 1180 49B 0000E5C6 _CIcos = __CIcos | 1181 49C 0000E682 _CIlog = __CIlog I tried linking an old, big project with ntdll.dll. That project also uses libcmt.dll (/MT) and it uses many functions which are available in both places. Even so, I get only one error: >LIBCMT.lib(_wctype.obj) : error LNK2005: _iswdigit already defined in ntdll.lib(ntdll.dll) Is there a way to fix that? In general, is there a way to take what's available in ntdll.dll from ntdll.dll and anything not available there fromm libcmt.lib? -- - Vince |