Casting to int is notoriously slow. Maybe you’ve been living under a rock since x86-64, or otherwise missed that this hasn’t been true for a while on x86. 🙂 SSE/SSE2 have an instruction to convert with truncation (instead of the default rounding mode). The ISA supports this operation efficiently precisely because conversion with C semantics … Read more
TL;DR The discrepancy you are observing between RDTSC and REFTSC and is due to TurboBoost P-state transitions. During these transitions, most of the core, including the fixed-function performance counter REF_TSC, is halted for approximately 20000-21000 cycles (8.5us), but rdtsc continues at its invariant frequency. rdtsc is probably in an isolated power and clock domain because … Read more
In x86-64, 32-bit instructions implicitly zero-extend: bits 32-63 are cleared (to avoid false dependencies). So sometimes that’s why you’ll see odd-looking instructions. (Is mov %esi, %esi a no-op or not on x86-64?) However, in this case the previous mov-load is also 32-bit so the high half of %rax is already cleared. The mov %eax, %eax … Read more
I believe that you want to load the address of your string into %rsi; your code attempts to load a quadword from that address rather than the address itself. You want: lea msg(%rip), %rsi if I’m not mistaken. I don’t have a linux box to test on, however.
The extra code is for handling misalignment because the instruction used, vmovdqa64, requires 64 byte alignment. My testing shows that even though the standard doesn’t, gcc does allow a definition in another module to override the one here when in C mode. That definition might only comply with the basic alignment requirements (4 bytes) thus … Read more
I think it’s just R for “register”, since there are additional registers R8 – R15 on x86-64, and R is a common prefix on many CPU architectures where registers are numbered.
No, a 64-bit process can only load 64-bit DLLs and a 32-bit process can only load 32-bit DLLs. What you’re probably thinking of is that a 64-bit operating system can run 32-bit processes. The main issue with .NET is that – prior to VS2010 – executable projects defaulted to “AnyCPU” which means it would load … Read more
The high order bits are reserved in case the address bus would be increased in the future, so you can’t use it simply like that The AMD64 architecture defines a 64-bit virtual address format, of which the low-order 48 bits are used in current implementations (…) The architecture definition allows this limit to be raised … Read more
These instruction prefixes have no effect on modern processors (anything newer than Pentium 4). They just cost one byte of code space, and thus, not generating them is the right thing. For details, see Agner Fog’s optimization manuals, in particular 3. Microarchitecture: http://www.agner.org/optimize/ The “Intel® 64 and IA-32 Architectures Optimization Reference Manual” no longer mentions … Read more
If you just want to find this out on a given dll, then you can use the CorFlags tool that is part of the Windows SDK: CorFlags.exe assembly.dll If you want to do it using code, take a look at the GetPEKind method of the Module class: Assembly assembly = Assembly.LoadFrom(“path to dll”); PortableExecutableKinds peKind; … Read more