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
Well, first of all, jmp simply ‘jumps’ to the label that you give to it (which is a memory address as program instructions are stored in memory) while call stores the location where it will return (below the call instruction) in the stack, jmp to the label, and then at the ret instruction, jmp back … Read more
JNZ is short for “Jump if not zero (ZF = 0)”, and NOT “Jump if the ZF is set”. If it’s any easier to remember, consider that JNZ and JNE (jump if not equal) are equivalent. Therefore, when you’re doing cmp al, 47 and the content of AL is equal to 47, the ZF is … Read more
Something I found: * EAX – Accumulator Register * EBX – Base Register * ECX – Counter Register * EDX – Data Register * ESI – Source Index * EDI – Destination Index * EBP – Base Pointer * ESP – Stack Pointer
Carry Flag The rules for turning on the carry flag in binary/integer math are two: The carry flag is set if the addition of two numbers causes a carry out of the most significant (leftmost) bits added. 1111 + 0001 = 0000 (carry flag is turned on) The carry (borrow) flag is also set if … Read more
In this case CPU event refers to monitoring events per CPU rather than per task. For perf tools this restricts the usage of -C, –cpu= Count only on the list of CPUs provided. Multiple CPUs can be provided as a comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-2. In … Read more
i386 is just one the first model in the x86 familly of processors, and instructions sets. For more informations, you might want to take a look at : Intel 80386 x86 Quoting the second page : The term x86 refers to a family of instruction set architectures[1] based on the Intel 8086. The term is … Read more
Since we’ve covered the alignment issue, I would guess it’s this: http://en.wikipedia.org/wiki/Out-of-order_execution Since g++ issues a standalone load instruction, your processor can reorder the instructions to be pre-fetching the next data that will be needed while also adding and multiplying. MSVC throwing a pointer at mul makes the load and mul tied to the same … Read more
C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe” myproject.sln /Build “Release|x86
General part EDIT: Linux irrelevant parts removed While not totally wrong, narrowing down to int 0x80 and syscall oversimplifies the question as with sysenter there is at least a 3rd option. Using 0x80 and eax for syscall number, ebx, ecx, edx, esi, edi, and ebp to pass parameters is just one of many possible other … Read more