Re: Inquiry About PC-Relative Code Generation in QEMU

[Yip Coekjan]

Thank you for your response.

On 11/4/24 20:51:40, Richard Henderson wrote:

> User emulation does not have multiple mappings of the same physical page
> like system mode does.  This is because in user emulation we have only one
> process to emulate.

To clarify, is the reason QEMU does not use `CF_PCREL` for user emulation 
because it could potentially generate more opcodes, thus impacting 
performance?

> No.  Treating the guest code as PC as a variable instead of a constant is
> different from generating position independent host code.

I briefly went through `target/i386/tcg/translate.c` and noticed that when 
`CF_PCREL` is enabled, the generated opcodes seem to resemble PIC (Position-
Independent Code). My understanding is that `CF_PCREL` was not originally 
intended for generating PIC, but the host code generated does appear to be 
PIC. As I'm not very familiar with QEMU, please correct me if I'm mistaken.

Best regards,
Yip Coekjan