Linuxカーネル5.0ソースコメント
私はx86の詳細が下arch/x86にあり、syscallのものが下にあることを知っていましたarch/x86/entry。したがって、git grep rdiそのディレクトリをざっと見ると、arch / x86 / entry / entry_64.Sに移動します。
/*
* 64-bit SYSCALL instruction entry. Up to 6 arguments in registers.
*
* This is the only entry point used for 64-bit system calls. The
* hardware interface is reasonably well designed and the register to
* argument mapping Linux uses fits well with the registers that are
* available when SYSCALL is used.
*
* SYSCALL instructions can be found inlined in libc implementations as
* well as some other programs and libraries. There are also a handful
* of SYSCALL instructions in the vDSO used, for example, as a
* clock_gettimeofday fallback.
*
* 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
* then loads new ss, cs, and rip from previously programmed MSRs.
* rflags gets masked by a value from another MSR (so CLD and CLAC
* are not needed). SYSCALL does not save anything on the stack
* and does not change rsp.
*
* Registers on entry:
* rax system call number
* rcx return address
* r11 saved rflags (note: r11 is callee-clobbered register in C ABI)
* rdi arg0
* rsi arg1
* rdx arg2
* r10 arg3 (needs to be moved to rcx to conform to C ABI)
* r8 arg4
* r9 arg5
* (note: r12-r15, rbp, rbx are callee-preserved in C ABI)
*
* Only called from user space.
*
* When user can change pt_regs->foo always force IRET. That is because
* it deals with uncanonical addresses better. SYSRET has trouble
* with them due to bugs in both AMD and Intel CPUs.
*/
32ビットの場合は、arch / x86 / entry / entry_32.Sにあります。
/*
* 32-bit SYSENTER entry.
*
* 32-bit system calls through the vDSO's __kernel_vsyscall enter here
* if X86_FEATURE_SEP is available. This is the preferred system call
* entry on 32-bit systems.
*
* The SYSENTER instruction, in principle, should *only* occur in the
* vDSO. In practice, a small number of Android devices were shipped
* with a copy of Bionic that inlined a SYSENTER instruction. This
* never happened in any of Google's Bionic versions -- it only happened
* in a narrow range of Intel-provided versions.
*
* SYSENTER loads SS, ESP, CS, and EIP from previously programmed MSRs.
* IF and VM in RFLAGS are cleared (IOW: interrupts are off).
* SYSENTER does not save anything on the stack,
* and does not save old EIP (!!!), ESP, or EFLAGS.
*
* To avoid losing track of EFLAGS.VM (and thus potentially corrupting
* user and/or vm86 state), we explicitly disable the SYSENTER
* instruction in vm86 mode by reprogramming the MSRs.
*
* Arguments:
* eax system call number
* ebx arg1
* ecx arg2
* edx arg3
* esi arg4
* edi arg5
* ebp user stack
* 0(%ebp) arg6
*/
glibc 2.29 Linux x86_64システムコールの実装
次に、主要なlibc実装を調べて、それらが何をしているかを見てみましょう。
この回答を書いているときに、現在使用しているglibcを調べるよりも優れている点は何ですか？:-)
glibc 2.29はx86_64のsyscallsを定義しsysdeps/unix/sysv/linux/x86_64/sysdep.h、それにはいくつかの興味深いコードが含まれています。例：
/* The Linux/x86-64 kernel expects the system call parameters in
registers according to the following table:
syscall number rax
arg 1 rdi
arg 2 rsi
arg 3 rdx
arg 4 r10
arg 5 r8
arg 6 r9
The Linux kernel uses and destroys internally these registers:
return address from
syscall rcx
eflags from syscall r11
Normal function call, including calls to the system call stub
functions in the libc, get the first six parameters passed in
registers and the seventh parameter and later on the stack. The
register use is as follows:
system call number in the DO_CALL macro
arg 1 rdi
arg 2 rsi
arg 3 rdx
arg 4 rcx
arg 5 r8
arg 6 r9
We have to take care that the stack is aligned to 16 bytes. When
called the stack is not aligned since the return address has just
been pushed.
Syscalls of more than 6 arguments are not supported. */
そして：
/* Registers clobbered by syscall. */
# define REGISTERS_CLOBBERED_BY_SYSCALL "cc", "r11", "cx"
#undef internal_syscall6
#define internal_syscall6(number, err, arg1, arg2, arg3, arg4, arg5, arg6) \
({ \
unsigned long int resultvar; \
TYPEFY (arg6, __arg6) = ARGIFY (arg6); \
TYPEFY (arg5, __arg5) = ARGIFY (arg5); \
TYPEFY (arg4, __arg4) = ARGIFY (arg4); \
TYPEFY (arg3, __arg3) = ARGIFY (arg3); \
TYPEFY (arg2, __arg2) = ARGIFY (arg2); \
TYPEFY (arg1, __arg1) = ARGIFY (arg1); \
register TYPEFY (arg6, _a6) asm ("r9") = __arg6; \
register TYPEFY (arg5, _a5) asm ("r8") = __arg5; \
register TYPEFY (arg4, _a4) asm ("r10") = __arg4; \
register TYPEFY (arg3, _a3) asm ("rdx") = __arg3; \
register TYPEFY (arg2, _a2) asm ("rsi") = __arg2; \
register TYPEFY (arg1, _a1) asm ("rdi") = __arg1; \
asm volatile ( \
"syscall\n\t" \
: "=a" (resultvar) \
: "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4), \
"r" (_a5), "r" (_a6) \
: "memory", REGISTERS_CLOBBERED_BY_SYSCALL); \
(long int) resultvar; \
})
私はかなり自明だと思います。これが通常のSystem V AMD64 ABI関数の呼び出し規約に正確に一致するように設計されているように見えることに注意してください：https : //en.wikipedia.org/wiki/X86_calling_conventions#List_of_x86_calling_conventions
盗賊の簡単な注意：
ccフラグレジスタを意味します。しかしピーター・コーデスは、これはここでは不要であるとコメントしています。memory ポインタがアセンブリで渡され、メモリへのアクセスに使用される可能性があることを意味します
ゼロからの明示的な最小実行可能例については、この回答を参照してください：インラインアセンブリでsysenterを介してシステムコールを呼び出す方法？
アセンブリでいくつかのシステムコールを手動で作成する
あまり科学的ではありませんが、楽しいです：
x86_64.S
.text
.global _start
_start:
asm_main_after_prologue:
/* write */
mov $1, %rax /* syscall number */
mov $1, %rdi /* stdout */
mov $msg, %rsi /* buffer */
mov $len, %rdx /* len */
syscall
/* exit */
mov $60, %rax /* syscall number */
mov $0, %rdi /* exit status */
syscall
msg:
.ascii "hello\n"
len = . - msg
GitHubアップストリーム。
aarch64
私が最小限の実行可能なユーザランドの例を示しました：/reverseengineering/16917/arm64-syscalls-table/18834#18834ここにTODO grepのカーネルコード、簡単にする必要があります。
