Sergey Bugaev, le mar. 28 févr. 2023 17:14:05 +0300, a ecrit: > On Tue, Feb 28, 2023 at 4:26 PM Luca Dariz <l...@orpolo.org> wrote: > > >> + /* check if we need to place some arguments on the stack */ > > >> +_syscall64_args_stack: > > >> + mov EXT(mach_trap_table)(%rax),%r10 /* get number of arguments > > >> */ > > >> + subq $6,%r10 /* the first 6 args are already in > > >> place */ > > >> + jl _syscall64_call /* skip argument copy if >6 args */ > > > > > > jle? > > > > Right, I didn't test a 6-args syscall. > > > > >> + > > >> + movq R_UESP(%rbx),%r11 /* get user stack pointer */ > > >> + addq $8,%r11 /* Skip user return address */ > > >> + > > >> + mov $USER_DS,%r12 /* use user data segment for > > >> accesses */ > > >> + mov %r12,%fs > > >> + > > >> + lea (%r11,%r10,8),%r11 /* point past last argument */ > > Do I understand it right that for the most interesting syscall (which > takes 7 args!), I *am* supposed to pass the 7th arg on the stack (in > mem[rsp + 8])
That's the x86_64 ABI, yes. > -- unlike on Linux? ? Linux does put only 6 args in registers, too. Samuel
