The x86-64 System V ABi doc may help. It’s a reference, albeit lightweight. The Variable Argument List reference starts on page 54, then it goes on, page 56-57 documents va_list: The va_list Type The va_list type is an array containing a single element of one structure containing the necessary information to implement the va_arg macro. … Read more
Using –platform is correct. On my M1 Mac I’m able to run both arm64 and amd64 versions of the Ubuntu image from Docker Hub. The machine hardware name provided by uname proves it. # docker run –rm -ti –platform linux/arm/v7 ubuntu:latest uname -m armv7l # docker run –rm -ti –platform linux/amd64 ubuntu:latest uname -m x86_64 … Read more
The most likely cause of the speed improvement is that: inserting a MOV shifts the subsequent instructions to different memory addresses one of those moved instructions was an important conditional branch that branch was being incorrectly predicted due to aliasing in the branch prediction table moving the branch eliminated the alias and allowed the branch … Read more
In a manner of speaking, when you perform array (“indexed”) type addressing with general registers, you are doing essentially the same thing as the segment registers. In the bad old days of 8-bit and 16-bit programming, many applications required much more data (and occasionally more code) than a 16-bit address could reach. So many CPUs … Read more
Sometimes intrinsics are better understood in terms of the instruction they represent rather than as the abstract semantic given in their descriptions. The full set of the locality constants, as today, is #define _MM_HINT_T0 1 #define _MM_HINT_T1 2 #define _MM_HINT_T2 3 #define _MM_HINT_NTA 0 #define _MM_HINT_ENTA 4 #define _MM_HINT_ET0 5 #define _MM_HINT_ET1 6 #define _MM_HINT_ET2 … Read more
Addition and subtraction are the same, as is the low-half of a multiply. A full multiply, however, is not. Simple example: In 32-bit twos-complement, -1 has the same representation as the unsigned quantity 2**32 – 1. However: -1 * -1 = +1 (2**32 – 1) * (2**32 – 1) = (2**64 – 2**33 + 1) … Read more
Here’s what I could dig up myself, for x86-64 doing FP math with SSE2 (not legacy x87 where changing the rounding mode for C++’s truncation semantics was expensive): When I take a look at the generated assembly from clang and gcc, it looks like the cast int to double, it boils down to one instruction: … Read more
My question is whether the code in those libraries will allocate memory in the same heap as the main application or do they use their own heap? If the library uses the same malloc/free as the application (e.g. from glibc) – then yes, program and all libraries will use the single heap. If library uses … Read more
Accessing raw CPUID information is actually very easy, here is a C++ class for that which works in Windows, Linux and OSX: #ifndef CPUID_H #define CPUID_H #ifdef _WIN32 #include <limits.h> #include <intrin.h> typedef unsigned __int32 uint32_t; #else #include <stdint.h> #endif class CPUID { uint32_t regs[4]; public: explicit CPUID(unsigned i) { #ifdef _WIN32 __cpuid((int *)regs, (int)i); … Read more
It’s AT&T assembly syntax: source comes before destination mnemonic suffixes indicate the size of the operands (q for quad, etc.) registers are prefixed with % and immediate values with $ effective addresses are in the form DISP(BASE, INDEX, SCALE) (DISP + BASE + INDEX * SCALE) Indirect jump/call operands indicated with * (as opposed to … Read more