Mailing lists / fpc-devel / 2017-02
How to get pointer to class VMT in assembler block
2 messages · 2 people · –
- Bishop 1
- silvioprog 1
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Bishop wrote 7 lines
I need to get pointer to class VMT in assembler block. In pascal code this
can be done very simple, like Ptr := Pointer(SomeClass). But when i try in
assembler do like "MOV RAX, SomeClass" this make assembler syntax error. If
i try "LEA RAX, [SomeClass]" this compiled like "LEA RAX, [0]".
So, how get pointer to specefic class VMT in assembler block?
The assembler window (ctrl+alt+d) may help you to check what asm block fpc generated for its pascal code, for example, in my target (64 bits) the following asm block code was generated for a `ptr := pvmt(classtype)`:
...
unit1.pas:36 ptr := pvmt(classtype); 000000000045E7A1 488b45f0 mov -0x10(%rbp),%rax 000000000045E7A5 488b00 mov (%rax),%rax 000000000045E7A8 488945e0 mov %rax,-0x20(%rbp) 000000000045E7AC 488945e8 mov %rax,-0x18(%rbp)
and iirc the default asm syntax for my system (linux) is at&t.
hth
Silvio Clécio