From 9748bb8af86c131d45be1238ea4d5f965a974630 Mon Sep 17 00:00:00 2001 From: occheung Date: Fri, 20 Aug 2021 17:42:16 +0800 Subject: [PATCH] add riscv32 --- src/arch/mod.rs | 1 + src/arch/riscv32.rs | 219 ++++++++++++++++++++++++++++++++++++++++++++ src/lib.rs | 2 +- 3 files changed, 221 insertions(+), 1 deletion(-) create mode 100644 src/arch/riscv32.rs diff --git a/src/arch/mod.rs b/src/arch/mod.rs index 7aa16e2..faeb592 100644 --- a/src/arch/mod.rs +++ b/src/arch/mod.rs @@ -13,6 +13,7 @@ pub use self::imp::*; #[cfg_attr(target_arch = "x86_64", path = "x86_64.rs")] #[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")] #[cfg_attr(target_arch = "or1k", path = "or1k.rs")] +#[cfg_attr(target_arch = "riscv32", path = "riscv32.rs")] mod imp; #[cfg(test)] diff --git a/src/arch/riscv32.rs b/src/arch/riscv32.rs new file mode 100644 index 0000000..54e5a01 --- /dev/null +++ b/src/arch/riscv32.rs @@ -0,0 +1,219 @@ +// This file is part of libfringe, a low-level green threading library. +// Copyright (c) edef , +// whitequark +// Amanieu d'Antras +// Licensed under the Apache License, Version 2.0, or the MIT license , at your option. This file may not be +// copied, modified, or distributed except according to those terms. + +// To understand the machine code in this file, keep in mind these facts: +// * RISCV does not have a red zone. +// * RISCV requires (loosely) that the stack pointer (sp) should be 16 bytes +// aligned. +// * RISCV passes the first argument in a0. We also use a0 to pass a value +// while swapping context; this is an arbitrary choice +// (we clobber all registers and could use any of them) but this allows us +// to reuse the swap function to perform the initial call. We do the same +// thing with a1 to pass the stack pointer to the new context. +// +// To understand the DWARF CFI code in this file, keep in mind these facts: +// * CFI is "call frame information"; a set of instructions to a debugger or +// an unwinder that allow it to simulate returning from functions. This implies +// restoring every register to its pre-call state, as well as the stack pointer. +// * CFA is "call frame address"; the value of stack pointer right before the call +// instruction in the caller. Everything strictly below CFA (and inclusive until +// the next CFA) is the call frame of the callee. This implies that the return +// address is the part of callee's call frame. +// * Logically, DWARF CFI is a table where rows are instruction pointer values and +// columns describe where registers are spilled (mostly using expressions that +// compute a memory location as CFA+n). A .cfi_offset pseudoinstruction changes +// the state of a column for all IP numerically larger than the one it's placed +// after. A .cfi_def_* pseudoinstruction changes the CFA value similarly. +// * Simulating return is as easy as restoring register values from the CFI table +// and then setting stack pointer to CFA. +// +// A high-level overview of the function of the trampolines when unwinding is: +// * The 2nd init trampoline puts a controlled value (written in swap to `new_cfa`) +// into fp. This is then used as the CFA for the 1st trampoline. +// * This controlled value points to the bottom of the stack of the parent context, +// which holds the saved fp and ra from the call to swap(). +// * The 1st init trampoline tells the unwinder to restore fp and ra +// from the stack frame at fp (in the parent stack), thus continuing +// unwinding at the swap call site instead of falling off the end of context stack. +use core::mem; +use stack::Stack; + +pub const STACK_ALIGNMENT: usize = 16; + +#[derive(Debug, Clone, Copy)] +#[repr(transparent)] +pub struct StackPointer(*mut usize); + +pub unsafe fn init(stack: &Stack, f: unsafe extern "C" fn(usize, StackPointer) -> !) -> StackPointer { + #[naked] + unsafe extern "C" fn trampoline_1() { + llvm_asm!( + r#" + # gdb has a hardcoded check that rejects backtraces where frame addresses + # do not monotonically decrease. It is turned off if the function is called + # "__morestack" and that is hardcoded. So, to make gdb backtraces match + # the actual unwinder behavior, we call ourselves "__morestack" and mark + # the symbol as local; it shouldn't interfere with anything. + __morestack: + .local __morestack + + # Set up the first part of our DWARF CFI linking stacks together. When + # we reach this function from unwinding, fp will be pointing at the bottom + # of the parent linked stack. This link is set each time swap() is called. + # When unwinding the frame corresponding to this function, a DWARF unwinder + # will use fp+8 as the next call frame address, restore fp from CFA-4 and + # restore return address (ra) from CFA-8. This mirrors what the second half + # of `swap_trampoline` does. + .cfi_def_cfa fp, 16 + .cfi_offset fp, -12 + .cfi_offset ra, -16 + + # This nop is here so that the initial swap doesn't return to the start + # of the trampoline, which confuses the unwinder since it will look for + # frame information in the previous symbol rather than this one. It is + # never actually executed. + nop + + .Lend: + .size __morestack, .Lend-__morestack + "# + : : : : "volatile") + } + + #[naked] + unsafe extern "C" fn trampoline_2() { + llvm_asm!( + r#" + # Set up the second part of our DWARF CFI. + # When unwinding the frame corresponding to this function, a DWARF unwinder + # will restore fp (and thus CFA of the first trampoline) from the stack slot. + # This stack slot is updated every time swap() is called to point to the bottom + # of the stack of the context switch just switched from. + .cfi_def_cfa fp, 16 + .cfi_offset fp, -12 + .cfi_offset ra, -16 + + # This nop is here so that the return address of the swap trampoline + # doesn't point to the start of the symbol. This confuses gdb's backtraces, + # causing them to think the parent function is trampoline_1 instead of + # trampoline_2. + nop + + # Call the provided function. + # The function address is at offset 8 because sp will increment by 16 at the end + # of the swap, before calling trampoline_2. + lw a2, 8(sp) + jalr a2 + "# + : : : : "volatile") + } + + unsafe fn push(sp: &mut StackPointer, val: usize) { + sp.0 = sp.0.offset(-1); + *sp.0 = val + } + + // We set up the stack in a somewhat special way so that to the unwinder it + // looks like trampoline_1 has called trampoline_2, which has in turn called + // swap::trampoline. + // + // There are 2 call frames in this setup, each containing the return address + // followed by the fp value for that frame. This setup supports unwinding + // using DWARF CFI as well as the frame pointer-based unwinding used by tools + // such as perf or dtrace. + let mut sp = StackPointer(stack.base() as *mut usize); + + push(&mut sp, 0); // Make sure that the stack pointer is 16 bytes aligned + push(&mut sp, f as usize); // Function that trampoline_2 should call + + // Call frame for trampoline_2. The CFA slot is updated by swap::trampoline + // each time a context switch is performed. + push(&mut sp, 0xdead0cfa); // CFA slot + push(&mut sp, trampoline_1 as usize + 4); // Return after the nop + let frame = sp; + + push(&mut sp, 0); // Alignment + push(&mut sp, 0); // Alignment + + // Call frame for swap::trampoline. We set up the fp value to point to the + // parent call frame. + push(&mut sp, frame.0 as usize); // Pointer to parent call frame + push(&mut sp, trampoline_2 as usize + 4); // Entry point, skip initial nop + sp +} + +#[inline(always)] +pub unsafe fn swap(arg: usize, new_sp: StackPointer, + new_stack: Option<&Stack>) -> (usize, StackPointer) { + // Address of the topmost CFA stack slot. + let mut dummy: usize = mem::uninitialized(); + let new_cfa = if let Some(new_stack) = new_stack { + (new_stack.base() as *mut usize).offset(-3) + } else { + // Just pass a dummy pointer if we aren't linking the stack + &mut dummy + }; + + #[naked] + unsafe extern "C" fn trampoline() { + llvm_asm!( + r#" + # Save the frame pointer and link register by allocating 16 bytes + # from the stack; unwinder uses them to find the CFA of the caller, + # and so they have to have the correct value immediately after the + # call instruction that invoked the trampoline. + sw fp, -12(sp) + sw ra, -16(sp) + addi sp, sp, -16 + .cfi_offset fp, 4 + .cfi_offset ra, 0 + + # Link the call stacks together by writing the current stack bottom + # address to the CFA slot in the new stack. + sw sp, 0(a3) + + # Pass the stack pointer of the old context to the new one. + or a1, zero, sp + # Load stack pointer of the new context. + or sp, zero, a2 + # Deallocate the 16 bytes + addi sp, sp, 16 + + # Restore frame pointer and link register of the new context. + # Load frame and instruction pointers of the new context. + lw fp, -12(sp) + lw ra, -16(sp) + + # Return into the new context. + jr ra + "# + : : : : "volatile") + } + + let ret: usize; + let ret_sp: *mut usize; + llvm_asm!( + r#" + # Call the trampoline to switch to the new context. + jal ${2} + "# + : "={a0}" (ret) + "={a1}" (ret_sp) + : "s" (trampoline as usize) + "{a0}" (arg) + "{a2}" (new_sp.0) + "{a3}" (new_cfa) + :/*"zero",*/"ra",/*"sp","gp","tp",*/"t0","t1","t2", + /*"fp",*/"s1",/*"a0", "a1"*/"a2", "a3", "a4", "a5", + "a6", "a7", "s2", "s3", "s4", "s5", "s6", "s7", + "s8", "s9", "s10", "s11", "t3", "t4", "t5", "t6", + "memory" + : "volatile"); + (ret, StackPointer(ret_sp)) +} diff --git a/src/lib.rs b/src/lib.rs index c0b6cda..29e2a19 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -4,7 +4,7 @@ // http://apache.org/licenses/LICENSE-2.0> or the MIT license , at your option. This file may not be // copied, modified, or distributed except according to those terms. -#![feature(asm, naked_functions, untagged_unions)] +#![feature(llvm_asm, naked_functions, untagged_unions)] #![cfg_attr(feature = "alloc", feature(alloc, allocator_api))] #![cfg_attr(test, feature(test))] #![no_std]