Avoiding _memset?
in [Visual C]
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From: Alex Blekhman on 6 Sep 2009 15:02 "Vincent Fatica" wrote: > (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. > [...] > How do I avoid that (elegantly)? Is it some kind of > optimization I can simply turn off? I noticed that optimize for size (/O1) triggers the compiler to embed calls to memset. #pragma intrinsic(memset) has no any effect on this behavior. You can still leave optimize for speed (/O2) though. Also, do not set full optimization (/Ox). HTH Alex
From: Vincent Fatica on 6 Sep 2009 15:18 On Sun, 6 Sep 2009 22:02:13 +0300, "Alex Blekhman" <tkfx.REMOVE(a)yahoo.com> wrote: |"Vincent Fatica" wrote: |> (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. |> [...] |> How do I avoid that (elegantly)? Is it some kind of |> optimization I can simply turn off? | |I noticed that optimize for size (/O1) triggers the compiler to |embed calls to memset. #pragma intrinsic(memset) has no any effect |on this behavior. You can still leave optimize for speed (/O2) |though. Also, do not set full optimization (/Ox). That's what I'm doing. But I get "warning LNK4210: .CRT section exists;" -- - Vince
From: Alex Blekhman on 6 Sep 2009 15:34 "Vincent Fatica" wrote: > But I get "warning LNK4210: .CRT section exists;" According to MSDN you have some static/global code that requires CRT while it isn't available. Also, security checks (/GS) are tightly integrated with the CRT, so you need to ensure that /GS is not set for your project. I assume you already found this article: KB814472 - "You receive linker warnings when you build Managed Extensions for C++ DLL projects" http://support.microsoft.com/kb/814472 It talks about managed code mostly, but can give you some insight about what goes on. HTH Alex
From: Vincent Fatica on 6 Sep 2009 16:00 On Sun, 6 Sep 2009 22:34:27 +0300, "Alex Blekhman" <tkfx.REMOVE(a)yahoo.com> wrote: |KB814472 - "You receive linker warnings when you build Managed |Extensions for C++ DLL projects" |http://support.microsoft.com/kb/814472 I've seen that before. Mine is an utterly simple program (below). Without going out of my way at all, I apparently get the intrinsic wcslen() (no library, no warming, no .CRT section). memset() is another story! #include <windows.h> #include <intrin.h> INT MyWinMain(VOID) { WCHAR *pCmdLine = GetCommandLine(); INT argc; WCHAR **argv = CommandLineToArgvW(pCmdLine, &argc); pCmdLine += wcslen(argv[0]); while ( *pCmdLine && *pCmdLine != L' ' ) pCmdLine += 1; pCmdLine += 1; STARTUPINFO si; __stosb((UCHAR*) &si, 0, sizeof(si)); si.cb = sizeof(si); PROCESS_INFORMATION pi; CreateProcess(NULL, pCmdLine, NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi); LocalFree(argv); return 0; } -- - Vince
From: xiaosi on 6 Sep 2009 22:58
The titles of msdn are some misleading, while intrin.h is more truthful: ** __MACHINEI : Intel (32 bit x86) and X64 __MACHINEI(void __stosb(unsigned char *, unsigned char, size_t)) "Vincent Fatica" <vince(a)blackholespam.net> wrote: > On Mon, 7 Sep 2009 00:56:43 +0800, "xiaosi" <xiaosi(a)cn99.com> wrote: > > |You may use intrinsic __stosb to replace memset: > |#include <intrin.h> > | STARTUPINFO si; > | __stosb((unsigned char*)&si, 0, sizeof(si)); > | si.cb = sizeof(si); > > Thanks. That's interesting. There's something I wonder about. __stosb is > listed in the documentation's "x64 Intrinsics"; it is not listed in "x86 > Intrinsics". What's up with that? > -- > - Vince |