diff options
Diffstat (limited to 'arch/riscv/kernel/signal.cc')
| -rw-r--r-- | arch/riscv/kernel/signal.cc | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/arch/riscv/kernel/signal.cc b/arch/riscv/kernel/signal.cc new file mode 100644 index 0000000..39fe34e --- /dev/null +++ b/arch/riscv/kernel/signal.cc @@ -0,0 +1,163 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* Copyright (C) 2026 Richard Qin */ + +/* + * arch/riscv/signal.cc — Signal frame construction and sigreturn + * + * Constructs a signal frame on the user stack before returning to + * the user signal handler. On sigreturn, restores the original + * registers from the saved frame. + * + * Frame layout on user stack (grows downward): + * + * +-----------------------+ <- original sp + * | sigset_t saved_mask | 8 bytes + * | TrapFrame saved_regs | 296 bytes + * | kernel_siginfo info | 128 bytes + * +-----------------------+ <- new sp (16-byte aligned) + * + * Reference: Linux arch/riscv/kernel/signal.c + */ + +#include <lume/signal.h> +#include <lume/signal_types.h> +#include <lume/signal_nr.h> +#include <lume/task.h> +#include <lume/uaccess.h> +#include <lume/errno.h> +#include <lume/klog.h> +#include <arch/trapframe.h> + +/* ================================================================== */ +/* Signal frame layout */ +/* ================================================================== */ + +struct rt_sigframe { + kernel_siginfo info; /* siginfo for SA_SIGINFO handlers */ + arch::TrapFrame saved_regs; /* saved register state */ + sigset_t saved_mask; /* blocked mask to restore on sigreturn */ +}; + +/* ================================================================== */ +/* Signal trampoline (written to user stack) */ +/* ================================================================== */ + +/* + * When the user's signal handler returns (via `ret`), ra points here. + * This tiny code sequence invokes sys_rt_sigreturn to restore the + * original execution context. + * + * RISC-V instructions (8 bytes): + * li a7, 139 → addi a7, zero, 139 → 0x08b00893 + * ecall → 0x00000073 + */ +static constexpr uint32 sigreturn_trampoline[2] = { + 0x08b00893, /* li a7, 139 (SYS_rt_sigreturn) */ + 0x00000073, /* ecall */ +}; + +/* ================================================================== */ +/* setup_signal_frame */ +/* ================================================================== */ + +int setup_signal_frame(arch::TrapFrame* tf, int signo, + kernel_sigaction* ka, kernel_siginfo* info) +{ + TaskControlBlock* curr = current_task(); + if (!curr) return -EINVAL; + + /* Calculate frame location on user stack */ + uint64 sp = tf->sp; + + /* Reserve space for the trampoline below the frame */ + sp -= sizeof(sigreturn_trampoline); + sp &= ~15ULL; /* 16-byte align */ + uint64 trampoline_addr = sp; + + /* Reserve space for the signal frame */ + sp -= sizeof(rt_sigframe); + sp &= ~15ULL; /* 16-byte align */ + uint64 frame_addr = sp; + + /* Build the frame in kernel memory, then copy to user stack */ + rt_sigframe frame{}; + if (info) { + frame.info = *info; + } + frame.saved_regs = *tf; + frame.saved_mask = curr->blocked; + + /* Copy frame to user stack */ + int err = copy_to_user(frame_addr, &frame, sizeof(frame)); + if (err < 0) return -EFAULT; + + /* Copy trampoline to user stack */ + err = copy_to_user(trampoline_addr, sigreturn_trampoline, + sizeof(sigreturn_trampoline)); + if (err < 0) return -EFAULT; + + /* Set up the trap frame to execute the signal handler */ + tf->epc = ka->sa_handler; + tf->sp = frame_addr; + + /* Arguments to the handler: handler(int signo, siginfo_t*, ucontext_t*) */ + tf->a[0] = static_cast<uint64>(signo); + + if (ka->sa_flags & SA_SIGINFO) { + /* SA_SIGINFO: pass siginfo and ucontext pointers */ + tf->a[1] = frame_addr; /* &info */ + tf->a[2] = frame_addr + sizeof(kernel_siginfo); /* &saved_regs (as ucontext) */ + } else { + tf->a[1] = 0; + tf->a[2] = 0; + } + + /* Return address: when the handler does `ret`, jump to trampoline */ + if (ka->sa_flags & SA_RESTORER) { + tf->ra = ka->sa_restorer; + } else { + tf->ra = trampoline_addr; + } + + return 0; +} + +/* ================================================================== */ +/* arch_sigreturn — restore state from signal frame */ +/* ================================================================== */ + +int64 arch_sigreturn(arch::TrapFrame* tf) +{ + TaskControlBlock* curr = current_task(); + if (!curr) return -EINVAL; + + /* + * The signal frame is located at the current sp. + * We need to read it back and restore the original state. + */ + uint64 frame_addr = tf->sp; + + rt_sigframe frame{}; + int err = copy_from_user(&frame, frame_addr, sizeof(frame)); + if (err < 0) { + printk(KERN_ERR "sigreturn: failed to read signal frame at %llx\n", + frame_addr); + task_kill_current(SIGSEGV); + return -EFAULT; + } + + /* Restore the saved register state */ + *tf = frame.saved_regs; + + /* Restore the blocked mask */ + curr->blocked = frame.saved_mask; + curr->blocked.del(SIGKILL); + curr->blocked.del(SIGSTOP); + + /* + * Return value: we return the saved a0 from the original context. + * The syscall dispatch will NOT overwrite a0 because sigreturn + * is special — it returns via the restored trap frame directly. + */ + return tf->a[0]; +} |