Bryand and O'Hallaron
                             Chapter 3 Section 3.6.3
                               Jump Instructions


1. Figure 3.11 The Jump Instruction 

Instruction    Synonym     Jump condition      Description

jmp  Label                 1                   Direct jump
jmp  *Operand              1                   Indirect jump

je   Label     jz          ZF                  Equal / zero
jne  Label     jnz         ~ZF                 Noe equal / not zero

jg   Label     jnle        ~(SF^OF)&~ZF        Greater (signed >)
jge  Label     jnl         ~(SF^OF)            Greater or equal (signed >)
jl   Label     jnge        (SF^OF)             Less (signed <)
jle  Label     jng         SF^OF)|ZF           Less or equal (signed <=)

ja   Label     jnbe        ~CF&~ZF             Above (unsigned >)
jae  Label     jnb         ~CF                 Above or equal (unsigned >)
jb   Label     jnae        CF                  Below (unsigned <)
jbe  Label     jna         CF&~ZF              Below or equal (unsigned <=)


2. Examples

       jmp   .L1         # direct jump (address part of instruction)
       .p2align 4,,15
  .L1                    # start at an aligned address


       leal  .L1,%eax   
       jmp   *%eax       # indirect jump (address in %eax)
       .p2align 4,,15
  .L1                    # start at an aligned address


       leal  .L1,-8(%ebp)
       jmp   *-8(%ebp)   # indirect jump (address on stack)
       .p2align 4,,15
  .L1                    # start a loop at an aligned address
       

       leal  .L1,jmpadr
       jmp   *jmpadr     # indirect jump (address in jmpadr)
       .p2align 4,,15
  .L1                    # start a loop at an aligned address
        ...
       .bss              # data segment for data with initial value 0
       .align 4          # make sure the long is aligned
       .size   accum,4   # its a long
jmpadr:
       .zero   4         # initial value zero


3. PC (Program Counter) Relative Addressing (The Program Counter is a synonym
   for the Instruction Pointer (IP).
   
-----------------------------------------------------
storm:~/bando/chap3/sec6>more silly.c
extern int j;
main()
{
     int i = j;
     if (i <= 0) 
        goto end;
     while (i > 0) 
        i = i - (i >> 1);
end: return;
}
storm:~/bando/chap3/sec6>gcc -S -O2 silly.c
-----------------------------------------------------
storm:~/bando/chap3/sec6>more silly.s
        .file   "silly.c"
        .text
        .p2align 4,,15
.globl main
        .type   main, @function
main:
        leal    4(%esp), %ecx
        andl    $-16, %esp
        pushl   -4(%ecx)
        pushl   %ebp
        movl    %esp, %ebp
        pushl   %ecx
#---------------------------
        movl    j, %edx
        testl   %edx, %edx
        jle     .L5
        .p2align 4,,7
.L6:
        movl    %edx, %eax
        sarl    %eax
        subl    %eax, %edx
        testl   %edx, %edx
        jg      .L6
.L5:
        popl    %ecx
#---------------------------
        popl    %ebp
        leal    -4(%ecx), %esp
        ret
        .size   main, .-main
        .ident  "GCC: (GNU) 4.1.2 20070502 (Red Hat 4.1.2-12)"
        .section        .note.GNU-stack,"",@progbits
storm:~/bando/chap3/sec6>
-----------------------------------------------------
storm:~/bando/chap3/sec6>objdump -d silly.o
silly.o:     file format elf32-i386
Disassembly of section .text:
00000000 <main>:
   0:   8d 4c 24 04             lea    0x4(%esp),%ecx
   4:   83 e4 f0                and    $0xfffffff0,%esp
   7:   ff 71 fc                pushl  0xfffffffc(%ecx)
   a:   55                      push   %ebp
   b:   89 e5                   mov    %esp,%ebp
   d:   51                      push   %ecx
#---------------------------
   e:   8b 15 00 00 00 00       mov    0x0,%edx
  14:   85 d2                   test   %edx,%edx
  16:   7e 0a                   jle    22 <main+0x22>
  18:   89 d0                   mov    %edx,%eax
  1a:   d1 f8                   sar    %eax
  1c:   29 c2                   sub    %eax,%edx
  1e:   85 d2                   test   %edx,%edx
  20:   7f f6                   jg     18 <main+0x18>
  22:   59                      pop    %ecx
#---------------------------
  23:   5d                      pop    %ebp
  24:   8d 61 fc                lea    0xfffffffc(%ecx),%esp
  27:   c3                      ret    
-----------------------------------------------------
storm:~/bando/chap3/sec6>more definej.c
int j = 0;
storm:~/bando/chap3/sec6>gcc -o silly silly.s definej.c
storm:~/bando/chap3/sec6>objdump -d silly
...
08048380 <main>:
 8048380:       8d 4c 24 04             lea    0x4(%esp),%ecx
 8048384:       83 e4 f0                and    $0xfffffff0,%esp
 8048387:       ff 71 fc                pushl  0xfffffffc(%ecx)
 804838a:       55                      push   %ebp
 804838b:       89 e5                   mov    %esp,%ebp
 804838d:       51                      push   %ecx
#---------------------------
 804838e:       8b 15 f4 95 04 08       mov    0x80495f4,%edx
 8048394:       85 d2                   test   %edx,%edx
 8048396:       7e 0a                   jle    80483a2 <main+0x22>
 8048398:       89 d0                   mov    %edx,%eax
 804839a:       d1 f8                   sar    %eax
 804839c:       29 c2                   sub    %eax,%edx
 804839e:       85 d2                   test   %edx,%edx
 80483a0:       7f f6                   jg     8048398 <main+0x18>
 80483a2:       59                      pop    %ecx
#---------------------------
 80483a3:       5d                      pop    %ebp
 80483a4:       8d 61 fc                lea    0xfffffffc(%ecx),%esp
 80483a7:       c3                      ret    
 80483a8:       90                      nop    
 80483a9:       90                      nop    
 80483aa:       90                      nop    
...


4. Practice Problem 3.9 on page 157