Delphi汇编程序常量'eof' [英] Delphi assembler constant 'eof'

问题描述

在asm块上下文中似乎有一个未记录的常量 eof .使用Delphi 7对此进行了测试.

There seems to be an undocumented constant eof in asm block context. This was tested using Delphi 7.

program TestEof;
{$APPTYPE CONSOLE}
var
  example : Integer;
begin
  asm
    mov example, eof
  end;
  writeln(example);
  readln;
end.

这会打印出 14 .

该常量 eof 从何而来?它的值 $ 0E 或 14 来自何处?

Where does that constant eof and it's value value $0E or 14 come from?

这是编译结果

...
call @InitExe
// mov example, eof
mov [example], $0000000e
// writeln(example)
mov eax, [$004040a4]
mov edx, [example]
call @Write0Long
call @WriteLn
call @_IOTest
// readln;
...

推荐答案

Eof 实际上是

Eof is in fact a function defined in the System unit.

在我手头的Delphi 6和XE2的Delphi实现中， Eof 被实现为

In the implementations of Delphi that I have at hand, Delphi 6 and XE2, Eof is implemented as an intrinsic routine that results in a call to one of the following functions, as appropriate:

function _EofFile(var f: TFileRec): Boolean;
function _EofText(var t: TTextRec): Boolean;

我不知道为什么您的汇编代码变成了 mov [...]，$ 0000000e .您在注释中指出， System 单元本身利用了 asm 代码中的 eof ，例如，在 TextOpen .XE2中的相同代码现在是纯Pascal，并且搜索值 $ 1A 而不是 $ 0E .这似乎是一个实现细节.如果您想了解为什么会这样，那么我认为您需要对 System 单元中的代码进行反向工程，或者看看Embarcadero的工程师是否会向您解释实现.

I have no idea why your assembler code is turned into mov [...],$0000000e. You point out in a comment that the System unit itself makes use of eof in asm code, for example in TextOpen. The same code in XE2 is now pure Pascal and searches for a value of $1A instead of $0E. This would very much appear to be an implementation detail. If you want to understand why this is so then I think you will need to reverse engineer the code in the System unit, or see if the engineers at Embarcadero will explain the implementation to you.

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