1 // A WORD OF CAUTION 2 // 3 // This entire file basically needs to be kept in sync with itself. It's not 4 // really possible to modify just one bit of this file without understanding 5 // all the other bits. Documentation tries to reference various bits here and 6 // there but try to make sure to read over everything before tweaking things! 7 // 8 // Also at this time this file is heavily based off the x86_64 file, so you'll 9 // probably want to read that one as well. 10 11 use core::arch::naked_asm; 12 13 #[inline(never)] // FIXME(rust-lang/rust#148307) 14 pub(crate) unsafe extern "C" fn wasmtime_fiber_switch(top_of_stack: *mut u8) { 15 unsafe { wasmtime_fiber_switch_(top_of_stack) } 16 } 17 18 #[unsafe(naked)] 19 unsafe extern "C" fn wasmtime_fiber_switch_(top_of_stack: *mut u8 /* r0 */) { 20 naked_asm!( 21 " 22 // Save callee-saved registers 23 push {{r4-r11,lr}} 24 25 // Swap stacks, recording our current stack pointer 26 ldr r4, [r0, #-0x08] 27 str sp, [r0, #-0x08] 28 mov sp, r4 29 30 // Restore and return 31 pop {{r4-r11,lr}} 32 bx lr 33 ", 34 ); 35 } 36 37 pub(crate) unsafe fn wasmtime_fiber_init( 38 top_of_stack: *mut u8, 39 entry_point: extern "C" fn(*mut u8, *mut u8), 40 entry_arg0: *mut u8, 41 ) { 42 #[repr(C)] 43 #[derive(Default)] 44 struct InitialStack { 45 r4: *mut u8, 46 r5: *mut u8, 47 r6: *mut u8, 48 r7: *mut u8, 49 r8: *mut u8, 50 r9: *mut u8, 51 r10: *mut u8, 52 r11: *mut u8, 53 lr: *mut u8, 54 55 // unix.rs reserved space 56 last_sp: *mut u8, 57 run_result: *mut u8, 58 } 59 60 unsafe { 61 let initial_stack = top_of_stack.cast::<InitialStack>().sub(1); 62 initial_stack.write(InitialStack { 63 r9: entry_arg0, 64 r10: entry_point as *mut u8, 65 r11: top_of_stack, 66 lr: wasmtime_fiber_start as *mut u8, 67 last_sp: initial_stack.cast(), 68 ..InitialStack::default() 69 }); 70 } 71 } 72 73 #[unsafe(naked)] 74 unsafe extern "C" fn wasmtime_fiber_start() -> ! { 75 naked_asm!( 76 " 77 .cfi_startproc simple 78 .cfi_def_cfa_offset 0 79 // See the x86_64 file for more commentary on what these CFI directives 80 // are doing. Like over there note that the relative offsets to 81 // registers here match the frame layout in `wasmtime_fiber_switch`. 82 // 83 // TODO: this is only lightly tested. This gets backtraces in gdb but 84 // not at runtime. Perhaps the libgcc at runtime was too old? Doesn't 85 // support something here? Unclear. Will need investigation if someone 86 // ends up needing this and it still doesn't work. 87 .cfi_escape 0x0f, /* DW_CFA_def_cfa_expression */ \ 88 5, /* the byte length of this expression */ \ 89 0x7d, 0x00, /* DW_OP_breg14(%sp) + 0 */ \ 90 0x06, /* DW_OP_deref */ \ 91 0x23, 0x24 /* DW_OP_plus_uconst 0x24 */ 92 93 .cfi_rel_offset lr, -0x04 94 .cfi_rel_offset r11, -0x08 95 .cfi_rel_offset r10, -0x0c 96 .cfi_rel_offset r9, -0x10 97 .cfi_rel_offset r8, -0x14 98 .cfi_rel_offset r7, -0x18 99 .cfi_rel_offset r6, -0x1c 100 .cfi_rel_offset r5, -0x20 101 .cfi_rel_offset r4, -0x24 102 103 mov r1, r11 104 mov r0, r9 105 blx r10 106 .cfi_endproc 107 ", 108 ); 109 } 110