通过调用TemplateTable::_goto()函数来完成goto()指令的机器代码生成。如下：
// 将当前栈帧中保存的Method* 拷贝到rcx中 0x00007fffe101dd10: mov -0x18(%rbp),%rcx // 如果开启了profile则执行分支跳转相关的性能统计 // If no method data exists, go to profile_continue. // Otherwise, assign to mdp 0x00007fffe101dd14: mov -0x20(%rbp),%rax 0x00007fffe101dd18: test %rax,%rax 0x00007fffe101dd1b: je 0x00007fffe101dd39 // 将JumpData::taken_off_set存储到%rax中 0x00007fffe101dd21: mov 0x8(%rax),%rbx // 增加DataLayout::counter_increment，值为1 0x00007fffe101dd25: add $0x1,%rbx // sbb是带借位减法指令 0x00007fffe101dd29: sbb $0x0,%rbx // 存储回JumpData::taken_off_set中 0x00007fffe101dd2d: mov %rbx,0x8(%rax) // The method data pointer needs to be updated to reflect the new target. // 将JumpData::displacement_off_set // %rax中存储的是MethodData* 0x00007fffe101dd31: add 0x10(%rax),%rax // 将计算出的值存储到栈中interpreter_frame_mdx_offset偏向处 0x00007fffe101dd35: mov %rax,-0x20(%rbp) // **** profile_continue **** // 将当前字节码位置往后偏移1字节处开始的2字节数据读取到rdx中 0x00007fffe101dd39: movswl 0x1(%r13),%edx // 将rdx中的值字节次序变反 0x00007fffe101dd3e: bswap %edx // 将rdx中的值右移16位，上述两步就是为了计算跳转分支的偏移量 0x00007fffe101dd40: sar $0x10,%edx // 将rdx中的数据从2字节扩展成4字节 0x00007fffe101dd43: movslq %edx,%rdx // 将当前字节码地址加上rdx保存的偏移量，计算跳转的目标地址 0x00007fffe101dd46: add %rdx,%r13
如果UseLoopCounter为true时才会有如下汇编，在执行如下汇编时，各个寄存器的状态如下：
increment backedge counter for backward branches
rax: MDO ebx: MDO bumped taken-count rcx: method rdx: target offset r13: target bcp r14: locals pointer
汇编如下：
0x00007fffe101dd49: test %edx,%edx
0x00007fffe101dd4b: jns 0x00007fffe101de30 0x00007fffe101dd51: mov 0x20(%rcx),%rax 0x00007fffe101dd55: test %rax,%rax 0x00007fffe101dd58: jne 0x00007fffe101ddf4 0x00007fffe101dd5e: push %rdx 0x00007fffe101dd5f: push %rcx 0x00007fffe101dd60: callq 0x00007fffe101dd6a 0x00007fffe101dd65: jmpq 0x00007fffe101dde8 0x00007fffe101dd6a: mov %rcx,%rsi 0x00007fffe101dd6d: lea 0x8(%rsp),%rax 0x00007fffe101dd72: mov %r13,-0x38(%rbp) 0x00007fffe101dd76: mov %r15,%rdi 0x00007fffe101dd79: mov %rbp,0x200(%r15) 0x00007fffe101dd80: mov %rax,0x1f0(%r15) 0x00007fffe101dd87: test $0xf,%esp 0x00007fffe101dd8d: je 0x00007fffe101dda5 0x00007fffe101dd93: sub $0x8,%rsp 0x00007fffe101dd97: callq 0x00007ffff66b581c 0x00007fffe101dd9c: add $0x8,%rsp 0x00007fffe101dda0: jmpq 0x00007fffe101ddaa 0x00007fffe101dda5: callq 0x00007ffff66b581c 0x00007fffe101ddaa: movabs $0x0,%r10 0x00007fffe101ddb4: mov %r10,0x1f0(%r15) 0x00007fffe101ddbb: movabs $0x0,%r10 0x00007fffe101ddc5: mov %r10,0x200(%r15) 0x00007fffe101ddcc: cmpq $0x0,0x8(%r15) 0x00007fffe101ddd4: je 0x00007fffe101dddf 0x00007fffe101ddda: jmpq 0x00007fffe1000420 0x00007fffe101dddf: mov -0x38(%rbp),%r13 0x00007fffe101dde3: mov -0x30(%rbp),%r14 0x00007fffe101dde7: retq 0x00007fffe101dde8: pop %rcx 0x00007fffe101dde9: pop %rdx 0x00007fffe101ddea: mov 0x20(%rcx),%rax 0x00007fffe101ddee: je 0x00007fffe101de30 0x00007fffe101ddf4: mov 0x18(%rcx),%rbx 0x00007fffe101ddf8: test %rbx,%rbx 0x00007fffe101ddfb: je 0x00007fffe101de17 0x00007fffe101ddfd: mov 0x70(%rbx),%eax 0x00007fffe101de00: add $0x8,%eax 0x00007fffe101de03: mov %eax,0x70(%rbx) 0x00007fffe101de06: and $0x1ff8,%eax 0x00007fffe101de0c: je 0x00007fffe101df22 0x00007fffe101de12: jmpq 0x00007fffe101de30 0x00007fffe101de17: mov 0x20(%rcx),%rcx 0x00007fffe101de1b: mov 0xc(%rcx),%eax 0x00007fffe101de1e: add $0x8,%eax 0x00007fffe101de21: mov %eax,0xc(%rcx) 0x00007fffe101de24: and $0x1ff8,%eax 0x00007fffe101de2a: je 0x00007fffe101df22 0x00007fffe101de30: movzbl 0x0(%r13),%ebx 0x00007fffe101de35: movabs $0x7ffff73b9e40,%r10 0x00007fffe101de3f: jmpq *(%r10,%rbx,8) 0x00007fffe101de43: callq 0x00007fffe101de4d 0x00007fffe101de48: jmpq 0x00007fffe101dec8 0x00007fffe101de4d: lea 0x8(%rsp),%rax 0x00007fffe101de52: mov %r13,-0x38(%rbp) 0x00007fffe101de56: mov %r15,%rdi 0x00007fffe101de59: mov %rbp,0x200(%r15) 0x00007fffe101de60: mov %rax,0x1f0(%r15) 0x00007fffe101de67: test $0xf,%esp 0x00007fffe101de6d: je 0x00007fffe101de85 0x00007fffe101de73: sub $0x8,%rsp 0x00007fffe101de77: callq 0x00007ffff66b4d84 0x00007fffe101de7c: add $0x8,%rsp 0x00007fffe101de80: jmpq 0x00007fffe101de8a 0x00007fffe101de85: callq 0x00007ffff66b4d84 0x00007fffe101de8a: movabs $0x0,%r10 0x00007fffe101de94: mov %r10,0x1f0(%r15) 0x00007fffe101de9b: movabs $0x0,%r10 0x00007fffe101dea5: mov %r10,0x200(%r15) 0x00007fffe101deac: cmpq $0x0,0x8(%r15) 0x00007fffe101deb4: je 0x00007fffe101debf 0x00007fffe101deba: jmpq 0x00007fffe1000420 0x00007fffe101debf: mov -0x38(%rbp),%r13 0x00007fffe101dec3: mov -0x30(%rbp),%r14 0x00007fffe101dec7: retq 0x00007fffe101dec8: movzbl 0x0(%r13),%ebx 0x00007fffe101decd: push %rax 0x00007fffe101dece: push %rbx 0x00007fffe101decf: mov -0x18(%rbp),%rbx 0x00007fffe101ded3: mov 0x18(%rbx),%rax 0x00007fffe101ded7: test %rax,%rax 0x00007fffe101deda: je 0x00007fffe101df17 0x00007fffe101dee0: mov %r13,%rsi 0x00007fffe101dee3: mov %rbx,%rdi 0x00007fffe101dee6: test $0xf,%esp 0x00007fffe101deec: je 0x00007fffe101df04 0x00007fffe101def2: sub $0x8,%rsp 0x00007fffe101def6: callq 0x00007ffff66b4bb4 0x00007fffe101defb: add $0x8,%rsp 0x00007fffe101deff: jmpq 0x00007fffe101df09 0x00007fffe101df04: callq 0x00007ffff66b4bb4 0x00007fffe101df09: mov 0x18(%rbx),%rbx 0x00007fffe101df0d: add $0x90,%rbx 0x00007fffe101df14: add %rbx,%rax 0x00007fffe101df17: mov %rax,-0x20(%rbp) 0x00007fffe101df1b: pop %rbx 0x00007fffe101df1c: pop %rax 0x00007fffe101df1d: jmpq 0x00007fffe101de30 0x00007fffe101df22: neg %rdx 0x00007fffe101df25: add %r13,%rdx 0x00007fffe101df28: callq 0x00007fffe101df32 0x00007fffe101df2d: jmpq 0x00007fffe101dfb0 0x00007fffe101df32: mov %rdx,%rsi 0x00007fffe101df35: lea 0x8(%rsp),%rax 0x00007fffe101df3a: mov %r13,-0x38(%rbp) 0x00007fffe101df3e: mov %r15,%rdi 0x00007fffe101df41: mov %rbp,0x200(%r15) 0x00007fffe101df48: mov %rax,0x1f0(%r15) 0x00007fffe101df4f: test $0xf,%esp 0x00007fffe101df55: je 0x00007fffe101df6d 0x00007fffe101df5b: sub $0x8,%rsp 0x00007fffe101df5f: callq 0x00007ffff66b45c8 0x00007fffe101df64: add $0x8,%rsp 0x00007fffe101df68: jmpq 0x00007fffe101df72 0x00007fffe101df6d: callq 0x00007ffff66b45c8 0x00007fffe101df72: movabs $0x0,%r10 0x00007fffe101df7c: mov %r10,0x1f0(%r15) 0x00007fffe101df83: movabs $0x0,%r10 0x00007fffe101df8d: mov %r10,0x200(%r15) 0x00007fffe101df94: cmpq $0x0,0x8(%r15) 0x00007fffe101df9c: je 0x00007fffe101dfa7 0x00007fffe101dfa2: jmpq 0x00007fffe1000420 0x00007fffe101dfa7: mov -0x38(%rbp),%r13 0x00007fffe101dfab: mov -0x30(%rbp),%r14 0x00007fffe101dfaf: retq 0x00007fffe101dfb0: movzbl 0x0(%r13),%ebx 0x00007fffe101dfb5: test %rax,%rax 0x00007fffe101dfb8: je 0x00007fffe101de30 0x00007fffe101dfbe: mov 0x48(%rax),%ecx 0x00007fffe101dfc1: cmp $0xfffffffe,%ecx 0x00007fffe101dfc4: je 0x00007fffe101de30 0x00007fffe101dfca: mov %rax,%r13 0x00007fffe101dfcd: callq 0x00007fffe101dfd7 0x00007fffe101dfd2: jmpq 0x00007fffe101e052 0x00007fffe101dfd7: lea 0x8(%rsp),%rax 0x00007fffe101dfdc: mov %r13,-0x38(%rbp) 0x00007fffe101dfe0: mov %r15,%rdi 0x00007fffe101dfe3: mov %rbp,0x200(%r15) 0x00007fffe101dfea: mov %rax,0x1f0(%r15) 0x00007fffe101dff1: test $0xf,%esp 0x00007fffe101dff7: je 0x00007fffe101e00f 0x00007fffe101dffd: sub $0x8,%rsp 0x00007fffe101e001: callq 0x00007ffff6a18a6a 0x00007fffe101e006: add $0x8,%rsp 0x00007fffe101e00a: jmpq 0x00007fffe101e014 0x00007fffe101e00f: callq 0x00007ffff6a18a6a 0x00007fffe101e014: movabs $0x0,%r10 0x00007fffe101e01e: mov %r10,0x1f0(%r15) 0x00007fffe101e025: movabs $0x0,%r10 0x00007fffe101e02f: mov %r10,0x200(%r15) 0x00007fffe101e036: cmpq $0x0,0x8(%r15) 0x00007fffe101e03e: je 0x00007fffe101e049 0x00007fffe101e044: jmpq 0x00007fffe1000420 0x00007fffe101e049: mov -0x38(%rbp),%r13 0x00007fffe101e04d: mov -0x30(%rbp),%r14 0x00007fffe101e051: retq 0x00007fffe101e052: mov %rax,%rsi 0x00007fffe101e055: mov -0x8(%rbp),%rdx 0x00007fffe101e059: leaveq 0x00007fffe101e05a: pop %rcx 0x00007fffe101e05b: mov %rdx,%rsp 0x00007fffe101e05e: and $0xfffffffffffffff0,%rsp 0x00007fffe101e062: push %rcx 0x00007fffe101e063: jmpq *0x88(%r13)
原文：https://www.cnblogs.com/mazhimazhi/p/13819580.html