Binary Hacks memo

『Binary Hacks』(高林哲, 鵜飼文敏, 佐藤祐介, 浜地慎一郎, 首藤一幸)での覚え書き(とかつっこみとか), この本は手を動かしてみないと面白さ半減やね.

>% gcc hello.c && wc -c ./a.out
>  12893 ./a.out
>% gcc -s hello.c && wc -c ./a.out
>   2748 ./a.out

int func()
{ // この括弧と
    try {
    } catch (...) {
    }
} // この括弧が省略できる

    long pagesize = (int)sysconf(_SC_PAGESIZE);

class Udiv : public Xbyak::CodeGenerator {
    // 最適化された割り算コードの動的生成
    void generate(unsigned int dividend)
    {
        ...
        mov(edx, int(m));
        mul(edx);
        if (a) {
            add(eax, int(m));
            adc(edx, 0);
        }
        if (len) {
            shr(edx, len);
        }
        mov(eax, edx);
        ret();
    }

    ...

    Udiv udiv;
    udiv.generate(d);
    int (*div)(unsigned int) = (int (*)(unsigned int))udiv.getCode();

    for (int i = 0; i < 10000; i++) {
        int a = i / d;
        int b = div(i);
        assert(a == b);
    }

main()
{
    int a = 3;
    *(short*)&a = 4;
}
>gcc -O2 -Wstrict-aliasing=2 t.c
>warning: dereferencing type-punned pointer will break \
>strict-aliasing rules

extern "C" {
void __cyg_profile_func_enter(void *funcAddr, void *callSite)
__attribute__((no_instrument_function));
void __cyg_profile_func_exit(void *funcAddr, void *callSite)
__attribute__((no_instrument_function));
}

void __cyg_profile_func_enter(void *funcAddr, void *callSite)
{
    printf("enter=%p, from %p\n", funcAddr, callSite);
}

void __cyg_profile_func_exit(void *funcAddr, void *callSite)
{
    printf("leave=%p, from %p\n", funcAddr, callSite);
}

>g++ -O2 -c bfdsymbol.cpp
>g++ -finstrument-functions dump_symbols.cpp -o bfd -lbfd bfdsymbol.o

>cat dump_symbols.cpp
#include <stdio.h>
#include <stdlib.h>
#include "bfdsymbol.h"

extern "C" void func1()
{
}

void func2()
{
    func1();
    printf("this function is %s\n", GetSymbolString((void*)func2));
}

void func3()
{
    func2();
}

void func4()
{
    func2();
    func3();
}

int main(int argc, char *argv[])
{
    func3();
    func4();
    func2();
    return 0;
}

>./bfd
in main [0x8048e38]
  in func3 [0x8048d70]
    in func2 [0x8048cf2]
      in func1 [0x8048cc4]
this function is func2
  in func4 [0x8048dd2]
    in func2 [0x8048cf2]
      in func1 [0x8048cc4]
(snip)

; for FPU
%define IM 0x01
%define DM 0x02
%define ZM 0x04
%define OM 0x08
%define UM 0x10
%define PM 0x20

; for SSE2/SSE3
%define EIM (1<<7)
%define EDM (1<<8)
%define EZM (1<<9)
%define EOM (1<<10)
%define EUM (1<<11)
%define EPM (1<<12)

    segment_text

proc func
    ; FPUの例外マスク設定
    ; get cw
    push    eax
    fstcw   word [esp]
    pop     eax

    and     eax, ~(IM | DM | ZM |OM |UM | PM)

    ; set cw
    push    eax
    fldcw   word [esp] ; (1)
    pop     eax

    ; calc

    fldz
    fldz
    fdivp   st1 ; (2)
    faddp   st0 ; (3)

    ; SSE2の例外マスク設定
    ; get mxcsr
    push    eax
    stmxcsr [esp]
    and     dword [esp], ~(EIM | EDM | EZM | EOM | EUM | EPM)
    ldmxcsr [esp] ; (4)
    pop     eax

    pxor    xm0, xm0
    divps   xm0, xm0 ; (5)

    ret