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 #[unsafe(naked)] 14 pub(crate) unsafe extern "C" fn wasmtime_fiber_switch(top_of_stack: *mut u8 /* r0 */) { 15 naked_asm!( 16 " 17 // Save callee-saved registers 18 push {{r4-r11,lr}} 19 20 // Swap stacks, recording our current stack pointer 21 ldr r4, [r0, #-0x08] 22 str sp, [r0, #-0x08] 23 mov sp, r4 24 25 // Restore and return 26 pop {{r4-r11,lr}} 27 bx lr 28 ", 29 ); 30 } 31 32 #[unsafe(naked)] 33 pub(crate) unsafe extern "C" fn wasmtime_fiber_init( 34 top_of_stack: *mut u8, // r0 35 entry_point: extern "C" fn(*mut u8, *mut u8), // r1 36 entry_arg0: *mut u8, // r2 37 ) { 38 naked_asm!( 39 " 40 adr r3, {start} 41 str r3, [r0, #-0x0c] // => lr 42 str r0, [r0, #-0x10] // => r11 43 str r1, [r0, #-0x14] // => r10 44 str r2, [r0, #-0x18] // => r9 45 46 add r3, r0, #-0x2c 47 str r3, [r0, #-0x08] 48 bx lr 49 ", 50 start = sym wasmtime_fiber_start, 51 ); 52 } 53 54 #[unsafe(naked)] 55 unsafe extern "C" fn wasmtime_fiber_start() -> ! { 56 naked_asm!( 57 " 58 .cfi_startproc simple 59 .cfi_def_cfa_offset 0 60 // See the x86_64 file for more commentary on what these CFI directives 61 // are doing. Like over there note that the relative offsets to 62 // registers here match the frame layout in `wasmtime_fiber_switch`. 63 // 64 // TODO: this is only lightly tested. This gets backtraces in gdb but 65 // not at runtime. Perhaps the libgcc at runtime was too old? Doesn't 66 // support something here? Unclear. Will need investigation if someone 67 // ends up needing this and it still doesn't work. 68 .cfi_escape 0x0f, /* DW_CFA_def_cfa_expression */ \ 69 5, /* the byte length of this expression */ \ 70 0x7d, 0x00, /* DW_OP_breg14(%sp) + 0 */ \ 71 0x06, /* DW_OP_deref */ \ 72 0x23, 0x24 /* DW_OP_plus_uconst 0x24 */ 73 74 .cfi_rel_offset lr, -0x04 75 .cfi_rel_offset r11, -0x08 76 .cfi_rel_offset r10, -0x0c 77 .cfi_rel_offset r9, -0x10 78 .cfi_rel_offset r8, -0x14 79 .cfi_rel_offset r7, -0x18 80 .cfi_rel_offset r6, -0x1c 81 .cfi_rel_offset r5, -0x20 82 .cfi_rel_offset r4, -0x24 83 84 mov r1, r11 85 mov r0, r9 86 blx r10 87 .cfi_endproc 88 ", 89 ); 90 } 91