~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~~ System calls for the Linux kernel ~~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~ The kernel preserves every register except rax, rcx, and r11. The system ~ call number goes in rax, as does the return value. Parameters go in rdi, ~ rsi, rdx, r10, r8, and r9, in that order. [SysV] A.2.1. ~ ~ Notice that rsi is our control stack, so we have to save it (for ~ syscalls with at least two parameters). We can use the value stack to do ~ that, since rsp is preserved, or we can use one of the other registers. We ~ don't ourselves save other registers because our caller should do that, if ~ it cares. ~ ~ In the kernel source, you may find the following files useful to ~ reference: ~ ~ * arch/x86/entry/syscalls/syscall_64.tbl ~ * include/linux/syscalls.h ~ * include/linux/compat.h ~ ~ Don't be confused by tools/scripts/syscall.tbl, it's not for x86. ~ ~ This file loads early, before dynamic.e. So, although it superficially ~ appears to be able to do allocation and high-level flow control, those come ~ from the transforms, which means they're shallow implementations. The stuff ~ here can't be moved later, because input.e relies on it, and the dynamic ~ stuff relies on that. So, there's additional Linux functionality in another ~ file that loads later, linux-dynamic.e. ~ (call number -- return value) : syscall-0 [ here @ :rax pop-reg64 ~ syscall number syscall :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, call number -- return value) : syscall-1 [ here @ :rax pop-reg64 ~ syscall number :rdi pop-reg64 ~ first param syscall :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, second param, call number -- return value) : syscall-2 [ here @ :rsi :rbx mov-reg64-reg64 ~ save rsi :rax pop-reg64 ~ syscall number :rsi pop-reg64 ~ second param :rdi pop-reg64 ~ first param syscall :rbx :rsi mov-reg64-reg64 ~ restore rsi :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, second param, third param, call number -- return value) : syscall-3 [ here @ :rsi :rbx mov-reg64-reg64 ~ save rsi :rax pop-reg64 ~ syscall number :rdx pop-reg64 ~ third param :rsi pop-reg64 ~ second param :rdi pop-reg64 ~ first param syscall :rbx :rsi mov-reg64-reg64 ~ restore rsi :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, second param, third param, fourth param, call number ~ -- return value) : syscall-4 [ here @ :rsi :rbx mov-reg64-reg64 ~ save rsi :rax pop-reg64 ~ syscall number :r10 pop-extrareg64 ~ fourth param :rdx pop-reg64 ~ third param :rsi pop-reg64 ~ second param :rdi pop-reg64 ~ first param syscall :rbx :rsi mov-reg64-reg64 ~ restore rsi :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, second param, third param, fourth param, fifth param, ~ call number -- return value) : syscall-5 [ here @ :rsi :rbx mov-reg64-reg64 ~ save rsi :rax pop-reg64 ~ syscall number :r8 pop-extrareg64 ~ fifth param :r10 pop-extrareg64 ~ fourth param :rdx pop-reg64 ~ third param :rsi pop-reg64 ~ second param :rdi pop-reg64 ~ first param syscall :rbx :rsi mov-reg64-reg64 ~ restore rsi :rax push-reg64 ~ return value here ! ] ;asm ~ (first param, second param, third param, fourth param, fifth param, ~ sixth param, call number -- return value) : syscall-6 [ here @ :rsi :rbx mov-reg64-reg64 ~ save rsi :rax pop-reg64 ~ syscall number :r9 pop-extrareg64 ~ sixth param :r8 pop-extrareg64 ~ fifth param :r10 pop-extrareg64 ~ fourth param :rdx pop-reg64 ~ third param :rsi pop-reg64 ~ second param :rdi pop-reg64 ~ first param syscall :rbx :rsi mov-reg64-reg64 ~ restore rsi :rax push-reg64 ~ return value here ! ] ;asm ~ Raw system calls ~ ~~~~~~~~~~~~~~~~ ~ This does the Linux exit() system call, passing it an exit code taken ~ from the stack. It does not return. ~ ~ (exit code -- *) : sys-exit [ here @ 60 :rax mov-reg64-imm64 ~ syscall number :rdi pop-reg64 ~ exit code syscall ~ In the event we're still here, let's minimize confusion. hlt ~ This one, uniquely, doesn't need to be followed by the "next" macro. It ~ is, though, since ;asm does that anyway. here ! ] ;asm ~ This does the Linux write() system call, passing it an address from the ~ top of the stack and a length from the second position on the stack. It ~ writes to file descriptor 1, which is stdout. ~ ~ For our length parameter, we can pop directly from the stack into rdx, ~ which directly becomes the syscall parameter. For our address parameter, ~ the syscall wants it in rsi, which we also care about, so we have to do a ~ little juggling. ~ ~ (length to write, base address -- *) : sys-write [ here @ :rcx pop-reg64 ~ address from stack :rdx pop-reg64 ~ length from stack, passed directly :rsi push-reg64 ~ save rsi 1 :rax mov-reg64-imm64 ~ syscall number 1 :rdi mov-reg64-imm64 ~ file descriptor :rcx :rsi mov-reg64-reg64 ~ pass address syscall :rsi pop-reg64 ~ restore rsi here ! ] ;asm ~ (length to read, base address -- result code) : sys-read [ here @ :rcx pop-reg64 ~ address from stack :rdx pop-reg64 ~ length from stack, passed directly :rsi push-reg64 ~ save rsi 0 :rax mov-reg64-imm64 ~ syscall number 0 :rdi mov-reg64-imm64 ~ file descriptor :rcx :rsi mov-reg64-reg64 ~ pass address syscall :rsi pop-reg64 ~ restore rsi :rax push-reg64 ~ return length here ! ] ;asm