www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.ldc - LDC calling convention

reply Alexandru Militaru <alexandru.cmilitaru gmail.com> writes:
Hello!

I am trying to port a kernel module to D and I am using LDC to 
compile the code. I want to call a function with 7 arguments and 
after some debugging sessions I’ve observed that the second 
argument has a different value in the callee function than the 
one I am passing in the caller function. After I’ve inspected 
with objdump the kernel module it seems to me that the LDC places 
the parameters in registers in a weird order. Note that the 
calling convention was fine until now and everything worked. 
Maybe the problem is that the function has 7 arguments. In the 
kernel, the calling convention is: first 6 arguments in rdi, rsi, 
rdx, rcx, r8, r9 and then on the stack.

Here is an image with the assembly code generated: in the left, 
the instructions generated by GCC for the kernel, in the right, 
the instructions generated by LDC. The parameters are, in this 
order: 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16. Can someone 
explain to me why this is happening and how to solve it?

https://imgur.com/6sSMWIY
Apr 09
next sibling parent Radu <void null.pt> writes:
On Tuesday, 9 April 2019 at 08:58:00 UTC, Alexandru Militaru 
wrote:
 Hello!

 I am trying to port a kernel module to D and I am using LDC to 
 compile the code. I want to call a function with 7 arguments 
 and after some debugging sessions I’ve observed that the second 
 argument has a different value in the callee function than the 
 one I am passing in the caller function. After I’ve inspected 
 with objdump the kernel module it seems to me that the LDC 
 places the parameters in registers in a weird order. Note that 
 the calling convention was fine until now and everything 
 worked. Maybe the problem is that the function has 7 arguments. 
 In the kernel, the calling convention is: first 6 arguments in 
 rdi, rsi, rdx, rcx, r8, r9 and then on the stack.

 [...]
The calling convention will be System V AMD64 ABI - a quick test shows that LDC passes the arguments in the expected order. https://godbolt.org/z/0H1yD5
Apr 09
prev sibling parent kinke <noone nowhere.com> writes:
It is the SysV ABI, with the exception that the 
arguments/parameters are reversed for extern(D) - the rightmost 
parameter is passed in the first register etc. That's what DMD 
does and required for compatibility with DMD-style inline 
assembly in druntime/Phobos.
Apr 10