inline-assembly

问题 As mentioned in title, i'm wondering that is there any way to compile a microsoft style inline-assembly code (as showed below) in a linux OS (e.g. ubuntu). _asm{ mov edi, A; .... EMMS; } The sample code is part of a inline-assembly code which can be compiled successfully on win10 with cl.exe compiler. Is there any way to compile it on linux? Do i have to rewrite it in GNU c/c++ style (i.e. __asm__{;;;})? 回答1: First of all, you should usually replace inline asm (with intrinsics or pure C)

问题 Consider this code, from my earlier question. int main(){ asm("movq $100000000, %rcx;" "startofloop: ; " "sub $0x1, %rcx; " "jne startofloop; "); } I would like to make number of iterations of the loop a C variable, so I tried the following after reading this document. int main(){ int count = 100000000; asm("movq %0, %rcx;" "startofloop: ; " "sub $0x1, %rcx; " "jne startofloop; ":: "r"(count)); } Unfortunately, this fails to compile, and breaks with the following error. asm_fail.c: In

问题 What is the best way to implement multiple versions of the same function that uses a specific CPU instructions if available (tested at run time), or falls back to a slower implementation if not? For example, x86 BMI2 provides a very useful PDEP instruction. How would I write a C code such that it tests BMI2 availability of the executing CPU on startup, and uses one of the two implementations -- one that uses _pdep_u64 call (available with -mbmi2 ), and another that does bit manipulation "by

问题 GCC's inline assembler recognizes the declarators =r and =&r . These make sense to me: the =r lets the assembler reuse an input register for output. However, GCC's inline assembler also recognizes the declarators +r and +&r . These make less sense to me. After all, isn't the distinction between +r and +&r a distinction without a difference? Does the +r alone not suffice to tell the compiler to reserve a register for the sole use of a single variable? For example, what is wrong with the

问题 first, if somebody knows a function of the Standard C Library, that prints a string without looking for a binary zero, but requires the number of characters to draw, please tell me! Otherwise, I have this problem: void printStringWithLength(char *str_ptr, int n_chars){ asm("mov 4, %rax");//Function number (write) asm("mov 1, %rbx");//File descriptor (stdout) asm("mov $str_ptr, %rcx"); asm("mov $n_chars, %rdx"); asm("int 0x80"); return; } GCC tells the following error to the "int" instruction:

问题 first, if somebody knows a function of the Standard C Library, that prints a string without looking for a binary zero, but requires the number of characters to draw, please tell me! Otherwise, I have this problem: void printStringWithLength(char *str_ptr, int n_chars){ asm("mov 4, %rax");//Function number (write) asm("mov 1, %rbx");//File descriptor (stdout) asm("mov $str_ptr, %rcx"); asm("mov $n_chars, %rdx"); asm("int 0x80"); return; } GCC tells the following error to the "int" instruction:

问题 I have the inline assembly code: #define read_msr(index, buf) asm volatile ("rdmsr" : "=d"(buf[1]), "=a"(buf[0]) : "c"(index)) The code using this macro: u32 buf[2]; read_msr(0x173, buf); I found the disassembly is(using gnu toolchain): mov eax,0x173 mov ecx,eax rdmsr mov DWORD PTR [rbp-0xc],edx mov DWORD PTR [rbp-0x10],eax The question is that 0x173 is less than 0xffff, why gcc does not use "mov cx, 0x173"? Will the gcc analysis the following instruction "rdmsr"? Will the gcc always know the

问题 Clang TargetInfo has a method called getClobbers : Returns a string of target-specific clobbers, in LLVM format. So, what is a clobber? 回答1: A clobbered register is a register which is trashed i.e. modified in unpredictable way by inline assembler. This usually happens when you need a temp. register or use particular instruction which happens to modify some register as a by-product. Usually programmer explicitly declares registers which are clobbered by his inline asm code but some may be

问题 Clang TargetInfo has a method called getClobbers : Returns a string of target-specific clobbers, in LLVM format. So, what is a clobber? 回答1: A clobbered register is a register which is trashed i.e. modified in unpredictable way by inline assembler. This usually happens when you need a temp. register or use particular instruction which happens to modify some register as a by-product. Usually programmer explicitly declares registers which are clobbered by his inline asm code but some may be

问题 Clang TargetInfo has a method called getClobbers : Returns a string of target-specific clobbers, in LLVM format. So, what is a clobber? 回答1: A clobbered register is a register which is trashed i.e. modified in unpredictable way by inline assembler. This usually happens when you need a temp. register or use particular instruction which happens to modify some register as a by-product. Usually programmer explicitly declares registers which are clobbered by his inline asm code but some may be