英文:
Is the `runtime.deferreturn` ever called in go defer
问题
在一个带有defer的Go函数的底部，汇编代码如下所示：
0x000000000047e1a0 <+256>: callq *%rsi
0x000000000047e1a2 <+258>: movb $0x0,0x7(%rsp)
0x000000000047e1a7 <+263>: mov 0x748(%rsp),%rdx
0x000000000047e1af <+271>: mov (%rdx),%rbx
0x000000000047e1b2 <+274>: callq *%rbx
0x000000000047e1b4 <+276>: mov 0x750(%rsp),%rbp
0x000000000047e1bc <+284>: add $0x758,%rsp
0x000000000047e1c3 <+291>: retq
0x000000000047e1c4 <+292>: callq 0x42ea40 <runtime.deferreturn>
0x000000000047e1c9 <+297>: mov 0x750(%rsp),%rbp
0x000000000047e1d1 <+305>: add $0x758,%rsp
0x000000000047e1d8 <+312>: retq
0x000000000047e1d9 <+313>: callq 0x458900 <runtime.morestack>
正如我们所看到的，调用runtime.deferreturn之前有一个retq指令。所以，看起来deferreturn永远不会被调用。我理解得对吗？
英文:
At the bottom of a Go func with defer, the assembly looks like this:
0x000000000047e1a0 <+256>: callq *%rsi
0x000000000047e1a2 <+258>: movb $0x0,0x7(%rsp)
0x000000000047e1a7 <+263>: mov 0x748(%rsp),%rdx
0x000000000047e1af <+271>: mov (%rdx),%rbx
0x000000000047e1b2 <+274>: callq *%rbx
0x000000000047e1b4 <+276>: mov 0x750(%rsp),%rbp
0x000000000047e1bc <+284>: add $0x758,%rsp
0x000000000047e1c3 <+291>: retq
0x000000000047e1c4 <+292>: callq 0x42ea40 <runtime.deferreturn>
0x000000000047e1c9 <+297>: mov 0x750(%rsp),%rbp
0x000000000047e1d1 <+305>: add $0x758,%rsp
0x000000000047e1d8 <+312>: retq
0x000000000047e1d9 <+313>: callq 0x458900 <runtime.morestack>
As we can see, there is a retq before call runtime.deferreturn. So, it seems that the deferreturn will never be called. Do I understand this right?
答案1
得分: 0
我们可以看到，在调用runtime.deferreturn之前有一个retq指令。所以，看起来deferreturn永远不会被调用。我理解得对吗？
英文:
> As we can see, there is a retq before call runtime.deferreturn. So, it seems that the deferreturn will never be called. Do I understand this right?
No. The code may be used by the Go runtime, for example, while panicking.
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