You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
191 lines
6.0 KiB
191 lines
6.0 KiB
#pragma once
|
|
|
|
#include <assert.h>
|
|
#include <stdbool.h>
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
#include <ucontext.h>
|
|
#include <unistd.h>
|
|
|
|
#include "arch_context.h"
|
|
#include "software_interrupt.h"
|
|
|
|
#define ARCH_SIG_JMP_OFF 8
|
|
|
|
// Userspace Registers.
|
|
enum UREGS
|
|
{
|
|
UREG_RSP = 0,
|
|
UREG_RIP = 1,
|
|
UREG_COUNT
|
|
};
|
|
|
|
typedef uint64_t reg_t;
|
|
|
|
/*
|
|
* This is the slowpath switch to a preempted sandbox!
|
|
* SIGUSR1 on the current thread and restore mcontext there!
|
|
*/
|
|
|
|
struct arch_context {
|
|
reg_t regs[UREG_COUNT];
|
|
mcontext_t mctx;
|
|
};
|
|
|
|
extern __thread struct arch_context worker_thread_base_context;
|
|
|
|
static void __attribute__((noinline)) arch_context_init(struct arch_context *actx, reg_t ip, reg_t sp)
|
|
{
|
|
memset(&actx->mctx, 0, sizeof(mcontext_t));
|
|
memset((void *)actx->regs, 0, sizeof(reg_t) * UREG_COUNT);
|
|
|
|
if (sp) {
|
|
/*
|
|
* context_switch conventions: bp is expected to be on top of the stack
|
|
* when co-op context switching..
|
|
*
|
|
* Temporarily switches the active stack to the stack pointer stored in sp
|
|
* to push the stack pointer sp to the top of its own stack.
|
|
* This acts as the base pointer
|
|
*/
|
|
asm volatile("movq %%rsp, %%rbx\n\t" /* Temporarily save pointer of active stack to B */
|
|
"movq %%rax, %%rsp\n\t" /* Set active stack to stack pointer in A(C variable sp) */
|
|
"pushq %%rax\n\t" /* Push A(C variable sp) onto the stack at sp */
|
|
"movq %%rsp, %%rax\n\t" /* Write the incremented stack pointer to A(C variable sp) */
|
|
"movq %%rbx, %%rsp\n\t" /* Restore original stack saved in B */
|
|
: "=a"(sp)
|
|
: "a"(sp)
|
|
: "memory", "cc", "rbx");
|
|
}
|
|
|
|
actx->regs[UREG_RSP] = sp;
|
|
actx->regs[UREG_RIP] = ip;
|
|
}
|
|
|
|
/**
|
|
* Preempt the current sandbox and start executing the next sandbox
|
|
* @param mc - the context of the current thread of execution
|
|
* @param ctx - the context that we want to restore
|
|
* @return Return code in {0,1}
|
|
* 0 = context restored successfully.
|
|
* 1 = special processing because thread was last in a user-level context switch state
|
|
*/
|
|
static int
|
|
arch_mcontext_restore(mcontext_t *mc, struct arch_context *ctx)
|
|
{
|
|
assert(ctx != &worker_thread_base_context);
|
|
assert(!software_interrupt_is_enabled());
|
|
|
|
/* if ctx->regs[0] is set, this was last in a user-level context switch state!
|
|
* else restore mcontext..
|
|
*/
|
|
bool did_user_level_context_switch = ctx->regs[UREG_RSP];
|
|
if (did_user_level_context_switch) {
|
|
mc->gregs[REG_RSP] = ctx->regs[UREG_RSP];
|
|
mc->gregs[REG_RIP] = ctx->regs[UREG_RIP] + ARCH_SIG_JMP_OFF;
|
|
ctx->regs[UREG_RSP] = 0;
|
|
|
|
return 1;
|
|
}
|
|
|
|
/* Restore mcontext */
|
|
memcpy(mc, &ctx->mctx, sizeof(mcontext_t));
|
|
memset(&ctx->mctx, 0, sizeof(mcontext_t));
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* Save the context of the currently executing process
|
|
* @param ctx - destination
|
|
* @param mc - source
|
|
*/
|
|
static void
|
|
arch_mcontext_save(struct arch_context *ctx, mcontext_t *mc)
|
|
{
|
|
assert(ctx != &worker_thread_base_context);
|
|
|
|
ctx->regs[UREG_RSP] = 0;
|
|
memcpy(&ctx->mctx, mc, sizeof(mcontext_t));
|
|
}
|
|
|
|
/**
|
|
* @param current - the registers and context of the thing running
|
|
* @param next - the registers and context of what we're switching to
|
|
* @return always returns 0, indicating success
|
|
*
|
|
* NULL in either of these values indicates the "no sandbox to execute" state,
|
|
* which defaults to resuming execution of main
|
|
*/
|
|
static inline int
|
|
arch_context_switch(struct arch_context *current, struct arch_context *next)
|
|
{
|
|
/* if both current and next are NULL, there is no state change */
|
|
assert(current != NULL || next != NULL);
|
|
|
|
/* Assumption: The caller does not switch to itself */
|
|
assert(current != next);
|
|
|
|
/* Set any NULLs to worker_thread_base_context to resume execution of main */
|
|
if (current == NULL) current = &worker_thread_base_context;
|
|
if (next == NULL) next = &worker_thread_base_context;
|
|
|
|
reg_t *current_registers = current->regs, *next_registers = next->regs;
|
|
assert(current_registers && next_registers);
|
|
|
|
asm volatile(
|
|
/* Create a new stack frame */
|
|
"pushq %%rbp\n\t" /* stack[stack_len++] = base_pointer */
|
|
"movq %%rsp, %%rbp\n\t" /* base_pointer = stack_pointer. Start new Frame */
|
|
|
|
/*
|
|
* Save the IP and stack pointer to the context of the sandbox we're switching from
|
|
*/
|
|
"movq $2f, 8(%%rax)\n\t" /* Write the address of label 2 to current_registers[1] (instruction_pointer). */
|
|
"movq %%rsp, (%%rax)\n\t" /* current_registers[0] (stack_pointer) = stack_pointer */
|
|
|
|
/*
|
|
* Check if the variant of the context we're trying to switch to is SLOW (mcontext-based)
|
|
* If it is, jump to label 1 to restore the preempted sandbox
|
|
*/
|
|
"cmpq $0, (%%rbx)\n\t" /* if (stack pointer == 0) */
|
|
"je 1f\n\t" /* goto 1; restore the existing sandbox using mcontext */
|
|
|
|
/*
|
|
* Fast Path
|
|
* We can just write update the stack pointer and jump to the target instruction
|
|
*/
|
|
"movq (%%rbx), %%rsp\n\t" /* stack_pointer = next_registers[0] (stack_pointer) */
|
|
"jmpq *8(%%rbx)\n\t" /* immediate jump to next_registers[1] (instruction_pointer) */
|
|
|
|
/*
|
|
* Slow Path
|
|
* If the stack pointer equaled 0, that means the sandbox was preempted and we need to
|
|
* fallback to a full mcontext-based context switch. We do this by invoking
|
|
* arch_context_mcontext_restore, which fires a SIGUSR1 signal. The SIGUSR1 signal handler
|
|
* executes the mcontext-based context switch.
|
|
*/
|
|
"1:\n\t"
|
|
"call arch_context_mcontext_restore\n\t"
|
|
".align 8\n\t"
|
|
|
|
/*
|
|
* Where preempted sandbox resumes
|
|
* rbx contains the preempted sandbox's IP and SP in this context
|
|
*/
|
|
"2:\n\t"
|
|
"movq $0, (%%rbx)\n\t" /* stack pointer = 0 */
|
|
".align 8\n\t"
|
|
|
|
/* This label is used in conjunction with a static offset */
|
|
"3:\n\t"
|
|
"popq %%rbp\n\t" /* base_pointer = stack[--stack_len]; Base Pointer is restored */
|
|
:
|
|
: "a"(current_registers), "b"(next_registers)
|
|
: "memory", "cc", "rcx", "rdx", "rsi", "rdi", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15", "xmm0",
|
|
"xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7", "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13",
|
|
"xmm14", "xmm15");
|
|
|
|
return 0;
|
|
}
|