[PATCH] LoongArch: Add Syscall Assembly Implementation

[Xi Ruoyao]

On Thu, 2023-03-23 at 14:12 +0100, Andreas Schwab wrote:
> On Mär 23 2023, caiyinyu wrote:
> 
> > Without this patch(objdump -d libc.so...):
> > 
> > 00000000000dd45c <syscall>:
> >    dd45c:       02fec063        addi.d          $sp, $sp, -80(0xfb0)
> >    dd460:       02c0606c        addi.d          $t0, $sp, 24(0x18)
> >    dd464:       29c06065        st.d            $a1, $sp, 24(0x18)
> >    dd468:       29c08066        st.d            $a2, $sp, 32(0x20)
> >    dd46c:       29c0a067        st.d            $a3, $sp, 40(0x28)
> >    dd470:       29c0c068        st.d            $a4, $sp, 48(0x30)
> >    dd474:       29c0e069        st.d            $a5, $sp, 56(0x38)
> >    dd478:       29c1206b        st.d            $a7, $sp, 72(0x48)
> >    dd47c:       29c1006a        st.d            $a6, $sp, 64(0x40)
> 
> If the argument registers are call-clobbbered, why does the compiler
> need to save them?

It seems triggered by va_start.  If I don't use "..." and replace it
with "a0, a1, a2, ..., a5", and remove va_start ... va_end, the compiled
code won't save registers.

I'll try to investigate further.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University