Linux arm64 系统调用过程学习记录
Linux5.10 arm64 系统调用过程学习记录
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- 用户态
- svc
- 内核态
- 相关数据结构
- 系统调用表
- 参考
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用户态
#include 编译，追踪
uname -a
Linux 5.11.0-27-generic #29~20.04.1-Ubuntu SMP Wed Aug 11 15:58:17 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
gcc write_test.c -o write_test
ldd write_test # ldd 用于打印程序或者库文件所依赖的共享库列表
# 输出
linux-vdso.so.1 (0x00007ffd3e37d000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fa3bfe90000)
/lib64/ld-linux-x86-64.so.2 (0x00007fa3c009b000)
svc
Supervisor Call causes an exception to be taken to EL1.On executing an SVC instruction, the PE records the exception as a Supervisor Call exception in ESR_ELx, using the EC value 0x15 , and the value of the immediate argument.
内核态
// arch/arm64/kernel/entry-common.c
asmlinkage void noinstr el0_sync_handler(struct pt_regs *regs) {
unsigned long esr = read_sysreg(esr_el1);
switch (ESR_ELx_EC(esr)) {
// arch/arm64/include/asm :
// #define ESR_ELx_EC_SVC64 (0x15)
case ESR_ELx_EC_SVC64:
el0_svc(regs);
break;
... // 其他异常
}
}
static void noinstr el0_svc(struct pt_regs *regs) {
...
do_el0_svc(regs);
}
// arch/arm64/kernel/syscall.c
void do_el0_svc(struct pt_regs *regs){
sve_user_discard();
// __NR_syscalls 系统调用总数
// sys_call_table 系统调用表 它每个系统调用的size是.long,即4byte
el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
}
static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
const syscall_fn_t syscall_table[]) {
unsigned long flags = current_thread_info()->flags;
regs->orig_x0 = regs->regs[0];
regs->syscallno = scno;
....
invoke_syscall(regs, scno, sc_nr, syscall_table);
....
}
static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
unsigned int sc_nr,
const syscall_fn_t syscall_table[])
{
long ret;
if (scno < sc_nr) {
syscall_fn_t syscall_fn;
syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
ret = __invoke_syscall(regs, syscall_fn);
} else {
// 未定义的系统调用，返回—ENOSYS
ret = do_ni_syscall(regs, scno);
}
if (is_compat_task())
ret = lower_32_bits(ret);
regs->regs[0] = ret;
}
static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn){
return syscall_fn(regs);
}
相关数据结构
// arch/arm64/include/asm/ptrace.h
struct pt_regs {
union {
struct user_pt_regs user_regs;
struct {
u64 regs[31];
u64 sp;
u64 pc;
u64 pstate;
};
};
u64 orig_x0;
#ifdef __AARCH64EB__
u32 unused2;
s32 syscallno;
#else
s32 syscallno;
u32 unused2;
#endif
u64 orig_addr_limit;
/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
u64 pmr_save;
u64 stackframe[2];
/* Only valid for some EL1 exceptions. */
u64 lockdep_hardirqs;
u64 exit_rcu;
};
// arch/arm64/include/asm/syscall.h
typedef long (*syscall_fn_t)(const struct pt_regs *regs);
系统调用表
// arch/arm64/kernel/sys.c
#undef __SYSCALL
#define __SYSCALL(nr, sym) asmlinkage long __arm64_##sym(const struct pt_regs *);
#include 通过上面文件的展开, 系统调用表为：
const syscall_fn_t sys_call_table[__NR_syscalls] = {
[0 ... __NR_syscalls - 1] = __arm64_sys_ni_syscall,__arm64_compat_sys_io_setup,__arm64_sys_io_destroy,......
};
系统调用宏
// arch/arm64/include/asm/syscall_wrapper.h
#define __SYSCALL_DEFINEx(x, name, ...) \
asmlinkage long __arm64_sys##name(const struct pt_regs *regs); \
ALLOW_ERROR_INJECTION(__arm64_sys##name, ERRNO); \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
asmlinkage long __arm64_sys##name(const struct pt_regs *regs) \
{ \
return __se_sys##name(SC_ARM64_REGS_TO_ARGS(x,__VA_ARGS__)); \
} \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
{ \
long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
__MAP(x,__SC_TEST,__VA_ARGS__); \
__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
return ret; \
} \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
#define SYSCALL_DEFINE0(sname) \
SYSCALL_METADATA(_##sname, 0); \
asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused); \
ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO); \
asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused)
// include/linux/syscalls.h
#ifndef SYSCALL_DEFINE0
#define SYSCALL_DEFINE0(sname) \
SYSCALL_METADATA(_##sname, 0); \
asmlinkage long sys_##sname(void); \
ALLOW_ERROR_INJECTION(sys_##sname, ERRNO); \
asmlinkage long sys_##sname(void)
#endif /* SYSCALL_DEFINE0 */
#define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE4(name, ...) SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
#define SYSCALL_DEFINE_MAXARGS 6
#define SYSCALL_DEFINEx(x, sname, ...) \
SYSCALL_METADATA(sname, x, __VA_ARGS__) \
__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
对于 write 系统调用宏展开
#define __NR_write 64 __SYSCALL(__NR_write, sys_write)
asmlinkage long __arm64_sys_write(const struct pt_regs *);
SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf, size_t, count) {
return ksys_write(fd, buf, count);
}
参考
- 系统调用实现原理
- Linux内核系统调用原理与实现
- Linux系统调用之SYSCALL_DEFINE