x86-64

This might be an exact duplicate of Is it possible to execute 32-bit code in 64-bit process by doing mode-switching? , but that question is from a year ago and only has one answer that doesn't give any source code. I'm hoping for more detailed answers. I'm running 64-bit Linux (Ubuntu 12.04, if it matters). Here's some code that allocates a page, writes some 64-bit code into it, and executes that code. #include <assert.h> #include <malloc.h> #include <stdio.h> #include <sys/mman.h> // mprotect #include <unistd.h> // sysconf unsigned char test_function[] = { 0xC3 }; // RET int main() { int

The Intel manuals for the RDTSC instruction warn that out of order execution can change when RDTSC is actually executed, so they recommend inserting a CPUID instruction in front of it because CPUID will serialize the instruction stream (CPUID is never executed out of order). My question is simple: if they had the ability to make instructions serializing, why didn't they make RDTSC serializing? The entire point of it appears to be to get cycle accurate timings. Is there a situation under which you would not want to precede it with a serializing instruction? Newer Intel CPUs have a separate

The Online LLVM demo page had an option to generate LLVM C++ API code as backend from a source code. However, that demo page is now disabled. I was wondering how we can do it ourselves using the available LLVM tools. I tried the following clang++ -c -emit-llvm input.cpp -o input.ll llc -march=cpp -o input.ll.cpp input.ll which gives the following error llc: error: invalid target 'cpp'. I am using LLVM/Clang version 3.2. Eli Bendersky The LLVM C++ backend has to be enabled during configuration when building LLVM. It's enabled by default in the configure (autotools) build, but not in the CMake

I am looking at some old code from a school project, and in trying to compile it on my laptop I ran into some problems. It was originally written for an old 32 bit version of gcc. Anyway I was trying to convert some of the assembly over to 64 bit compatible code and hit a few snags. Here is the original code: pusha pushl %ds pushl %es pushl %fs pushl %gs pushl %ss pusha is not valid in 64 bit mode. So what would be the proper way to do this in x86_64 assembly while in 64 bit mode? There has got to be a reason why pusha is not valid in 64 bit mode, so I have a feeling manually pushing all the

In 64 bit versions of windows, 32 bit software is installed in "c:\program files (x86)". This means you cannot use $(programfiles) to get the path to (32 bit) software. So I need a $(ProgramFiles32) to overcome this in my MSBuild project. I don't want to change the project depending on the os it is running on. I have a solution that I will post, but maybe there is a easier/better way. In MSBuild 4.0+, there's a $(MSBuildProgramFiles32) property for it, which you can confidently employ directly (especially if you're prepared to put a ToolsVersion="4.0" at the top of the file to guarantee it's