CODEWITHSUNDEEP
assemblyclang
Timocafé
Timocafé

Reputation: 765

How do you Mark ASM code?

I am trying to mark my ASM (generate by the compiler) to make a postpone analysis between my mark my analysis the corresponding .s file. The following MACRO works with GCC

#define ASM_LABEL(label) asm ("#" label "\n\t")

Nevertheless with CLANG the label is removed.

void kernel(double const * x, double * y){
    ASM_LABEL (START)
    y[0]+=x[1]+x[3]/x[4];
    y[1] = std::exp(x[0]);
    ASM_LABEL (STOP)
}

The generated ASM (clang -O3 -S) gives:

    movq    %rdi, -8(%rbp)
    movq    %rsi, -16(%rbp)
    ## InlineAsm Start
    ## InlineAsm End <---- no START mark
    movq    -8(%rbp), %rsi
    movsd   8(%rsi), %xmm0
    movq    -8(%rbp), %rsi
    ..............

The label has been deleted. Do you have any suggestion ? Does exist an generic tips ?

Thank you

Upvotes: 1

Views: 528

Answers (1)

halfflat
halfflat

Reputation: 1584

clang will, by default, use its integrated llvm assembler, but this can be disabled with the command line option -fno-integrated-as.

Specifying this along with -S should preserve the comments from the inline asm. Running clang -S -O3 -fno-integrated-as on the code sample

#include <cmath>
#define ASM_LABEL(label) asm ("#" label "\n\t" ::: "memory");

void kernel(double const * x, double * y){
    ASM_LABEL("START")
    y[0]+=x[1]+x[3]/x[4];
    y[1] = std::exp(x[0]);
    ASM_LABEL("STOP")
}

Gives the assembly (leaving out directives and labels):

pushq   %rbx
movq    %rsi, %rbx
#APP
#START

#NO_APP
movsd   24(%rdi), %xmm0
divsd   32(%rdi), %xmm0
addsd   8(%rdi), %xmm0
addsd   (%rbx), %xmm0
movsd   %xmm0, (%rbx)
movsd   (%rdi), %xmm0
callq   exp
movsd   %xmm0, 8(%rbx)
#APP
#STOP

#NO_APP
popq    %rbx
retq

Upvotes: 1

Related Questions