2.概述
UnwindCode这个东西，主要是通过一些二进制代码描述一些机器码含义，然后对其进行相应的操作。
我们通过lldb来看下这些操作的内容：
(lldb) b RunMainInternal
(lldb) r
(lldb) b allocUnwindInfo
(lldb) c
(lldb) source info
(lldb) b jitinterface.cpp:11232
(lldb) c内容如下：
lldb) c
Process 58851 resuming
Process 58851 stopped
* thread #1, name = 'clrrun', stop reason = breakpoint 6.1
frame #0: 0x00007ffff6e676c7 libcoreclr.so`CEEJitInfo::allocUnwindInfo(this=0x00007fffffffaf70, pHotCode="UH\x83\xecPH\x8dl$P\xc4A8W\xc0\xc5y\U0000007fE\xc0\xc5y\U0000007fE\xd0\xc5y\U0000007fE\xe03\xc0H\x89E\xf0H\x89}\xf8\x83=\xa9\xf3\U0000001d", pColdCode=0x0000000000000000, startOffset=0, endOffset=395, unwindSize=8, pUnwindBlock="\U00000001\U00000005\U00000002", funcKind=CORJIT_FUNC_ROOT) at jitinterface.cpp:11232:5
11229 }
11230 #endif // _DEBUG
11231
-> 11232 memcpy(pUnwindInfoRW, pUnwindBlock, unwindSize);我们看到它是一个memcpy的赋值。看下pUnwindInfoRW里面是什么
(lldb) n
(lldb) p/x *pUnwindInfoRW
(UNWIND_INFO) $6 = {
Version = 0x01
Flags = 0x00
SizeOfProlog = 0x05
CountOfUnwindCodes = 0x02
FrameRegister = 0x00
FrameOffset = 0x00
UnwindCode = {
[0] = {
= (CodeOffset = 0x05, UnwindOp = 0x02, OpInfo = 0x09)
EpilogueCode = (OffsetLow = 0x05, UnwindOp = 0x02, OffsetHigh = 0x09)
FrameOffset = 0x9205
}
}
}CountOfUnwindCodes表示总共有两个UnwindCode。
下面是UnwindCode成员意义：
CodeOffset表示机器码的长度。UnwindOp表示对是枚举类型_UNWIND_OP_CODES，表示机器码指令，比如UWOP_ALLOC_SMALL表示分配小对象栈空间(sub指令)，UWOP_PUSH_NONVOL(push指令)。OpInfo则表示机器操作数。
看下两个UnwindCode的结构
(lldb) p/x pUnwindInfoRW->UnwindCode[0]
(UNWIND_CODE) $12 = {
= (CodeOffset = 0x05, UnwindOp = 0x02, OpInfo = 0x09)
EpilogueCode = (OffsetLow = 0x05, UnwindOp = 0x02, OffsetHigh = 0x09)
FrameOffset = 0x9205
}
(lldb) p/x pUnwindInfoRW->UnwindCode[1]
(UNWIND_CODE) $13 = {
= (CodeOffset = 0x01, UnwindOp = 0x00, OpInfo = 0x05)
EpilogueCode = (OffsetLow = 0x01, UnwindOp = 0x00, OffsetHigh = 0x05)
FrameOffset = 0x5001
}
(lldb) p/x pUnwindInfoRW->UnwindCode[2]
(UNWIND_CODE) $14 = {
= (CodeOffset = 0x00, UnwindOp = 0x00, OpInfo = 0x00)
EpilogueCode = (OffsetLow = 0x00, UnwindOp = 0x00, OffsetHigh = 0x00)
FrameOffset = 0x0000
}第三个索引它就为零，确实是是两个。它的Unwindop分别是0x02和0x00.这分别代表了：UWOP_ALLOC_SMALL和UWOP_PUSH_NONVOL.也即机器码：sub和push。它的OpInfo分别为:0x09和0x05。分别代表了操作机器码：8* 9+8以及rbp。
OpInfo
if (OpInfo == kRBP)那么这个指令就很明显了
push rbp
sub rsp_80OK,以上是UnwindCode解析，下面来看下UnwindCode对于Risc-V和龙芯的这次hi。
Risc-v和龙芯
在它进行赋值完成之后，也即是：
memcpy(pUnwindInfoRW, pUnwindBlock, unwindSize);它总共有五个target，也就是指令集，分别为:amd64,arm64/arm,la64,riscv64
#elif defined(TARGET_AMD64)
pUnwindInfoRW->Flags = UNW_FLAG_EHANDLER | UNW_FLAG_UHANDLER;
#elif defined(TARGET_ARM64)
*(LONG *)pUnwindInfoRW |= (1 << 20); // X bit
#elif defined(TARGET_ARM)
*(LONG *)pUnwindInfoRW |= (1 << 20); // X bit
#elif defined(TARGET_LOONGARCH64)
*(LONG *)pUnwindInfoRW |= (1 << 20); // X bit
#elif defined(TARGET_RISCV64)
*(LONG *)pUnwindInfoRW |= (1 << 20); // X bit
#endif我们看到.Net的主线当中支持的Risc-v和La64，这里和x64的区别就在于，x64是pUnwindInfoRW的flag是或上
UNW_FLAG_EHANDLER | UNW_FLAG_UHANDLER;而其他的三个则是：
*(LONG *)pUnwindInfoRW |= (1 << 20);
