[Qemu-devel] How is address of helper function for slow path calculated ?

[Gaurav Sharma]

Hi,
I have been trying to trace the for how address translation is done for any load/store instructions. I was trying to emulate arm on an x86-64 machine.

However, i need some clarifications :

1. During the slow path, qemu uses helper functions to translate address.

2. This is done by calling the function itself during the execution.

3. The host instrn for the slow path is added at the end of the TB block. I tried a sample code and got the following host instrn :
0x2aaade72d120:  mov    %r14,%rdi
0x2aaade72d123:  xor    %edx,%edx
0x2aaade72d125:  lea    -0x42(%rip),%rcx        # 0x2aaade72d0ea
0x2aaade72d12c:  mov    $0x2afd98602c10,%r10
0x2aaade72d136:  callq  *%r10         // Call helper function
0x2aaade72d139:  mov    %eax,%ebp
0x2aaade72d13b:  jmpq   0x2aaade72d0ea

3. How does it gets the address of the helper function :

    call instruction is added by ' tcg_out_calli(s, (uintptr_t)qemu_ld_helpers[opc & ~MO_SIGN]' line of code which fetches the address of the helper function.

However from the assembly generated, the address is calculated before :
tcg_out_movi(s, TCG_TYPE_PTR, tcg_target_call_iarg_regs[3],
                     (uintptr_t)l->raddr)

How is the address for the helper function calculated ?

Thanks,

Gaurav