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.\"     @(#)syscall.2	8.1 (Berkeley) 6/16/93
.\"
.\"
.\" 2002-03-20  Christoph Hellwig <hch@infradead.org>
.\"	- adopted for Linux
.\" 2015-01-17, Kees Cook <keescook@chromium.org>
.\"	Added mips and arm64.
.\"
.\"*******************************************************************
.\"
.\" This file was generated with po4a. Translate the source file.
.\"
.\"*******************************************************************
.\"
.\" Japanese Version Copyright (c) 2002 Yuichi SATO
.\"         all rights reserved.
.\" Translated Tue Aug  6 03:43:25 JST 2002
.\"         by Yuichi SATO <ysato@h4.dion.ne.jp>
.\" Updated 2013-05-06, Akihiro MOTOKI <amotoki@gmail.com>
.\" Updated 2013-07-24, Akihiro MOTOKI <amotoki@gmail.com>
.\"
.TH SYSCALL 2 2020\-06\-09 Linux "Linux Programmer's Manual"
.SH 名前
syscall \- 間接システムコール
.SH 書式
.nf
\fB#include <unistd.h>\fP
\fB#include <sys/syscall.h>   \fP/* SYS_xxx の定義用 */
.PP
\fBlong syscall(long \fP\fInumber\fP\fB, ...);\fP
.fi
.PP
.RS -4
glibc 向けの機能検査マクロの要件 (\fBfeature_test_macros\fP(7)  参照):
.RE
 \fBsyscall\fP():
.PD 0
.ad l
.RS 4
.TP  4
glibc 2.19 以降:
 _DEFAULT_SOURCE
.TP 
glibc 2.19 より前:
 _BSD_SOURCE || _SVID_SOURCE
.RE
.ad
.PD
.SH 説明
\fBsyscall\fP() は、システムコールを起動する小さなライブラリ関数で、 \fInumber\fP
で指定されたアセンブリ言語インターフェースのシステムコールを、指定された引数をつけて実行する。 \fBsyscall\fP() が役に立つのは、例えば C
ライブラリにラッパー関数が存在しないシステムコールを呼び出したい場合である。
.PP
\fBsyscall\fP() は、システムコールを行う前に CPU
レジスターを保存し、システムコールから返った際にレジスターを復元し、システムコールが返したエラーを \fBerrno\fP(3) に格納する。
.PP
システムコールのシンボル定数は、ヘッダーファイル \fI<sys/syscall.h>\fP に書かれている。
.SH 返り値
返り値は呼び出されたシステムコールによって定義される。 一般に、返り値 0 は成功を表す。 \-1 はエラーを表し、エラー番号は \fIerrno\fP
に入れられる。
.SH 注意
\fBsyscall\fP()  は 4BSD で最初に登場した。
.SS アーキテクチャー固有の要件
各アーキテクチャーの ABI には、 システムコールの引数のカーネルへの渡し方に関する独自の要件がある。
(ほとんどのシステムコールのように) glibc ラッパー関数があるシステムコールでは、 glibc
が詳細を処理し、アーキテクチャーに応じた方法で引数が適切なレジスターにコピーされる。 しかし、 システムコールを呼び出すのに \fBsyscall\fP()
を使う場合には、 呼び出し側でアーキテクチャー依存の詳細を処理しなければならない場合がある。 これはいくつかの 32
ビットアーキテクチャーでは非常によくあることだ。
.PP
For example, on the ARM architecture Embedded ABI (EABI), a 64\-bit value
(e.g., \fIlong long\fP)  must be aligned to an even register pair.  Thus, using
\fBsyscall\fP()  instead of the wrapper provided by glibc, the \fBreadahead\fP(2)
system call would be invoked as follows on the ARM architecture with the
EABI in little endian mode:
.PP
.in +4n
.EX
 syscall(SYS_readahead, fd, 0,
        (unsigned int) (offset & 0xFFFFFFFF),
        (unsigned int) (offset >> 32),
        count);
.EE
.in
.PP
Since the offset argument is 64 bits, and the first argument (\fIfd\fP)  is
passed in \fIr0\fP, the caller must manually split and align the 64\-bit value
so that it is passed in the \fIr2\fP/\fIr3\fP register pair.  That means inserting
a dummy value into \fIr1\fP (the second argument of 0).  Care also must be
taken so that the split follows endian conventions (according to the C ABI
for the platform).
.PP
.\" Mike Frysinger: this issue ends up forcing MIPS
.\" O32 to take 7 arguments to syscall()
Similar issues can occur on MIPS with the O32 ABI, on PowerPC and parisc
with the 32\-bit ABI, and on Xtensa.
.PP
.\" See arch/parisc/kernel/sys_parisc.c.
Note that while the parisc C ABI also uses aligned register pairs, it uses a
shim layer to hide the issue from user space.
.PP
次のシステムコールに影響がある: \fBfadvise64_64\fP(2), \fBftruncate64\fP(2), \fBposix_fadvise\fP(2),
\fBpread64\fP(2), \fBpwrite64\fP(2), \fBreadahead\fP(2), \fBsync_file_range\fP(2),
\fBtruncate64\fP(2)
.PP
.\" You need to look up the syscalls directly in the kernel source to see if
.\" they should be in this list.  For example, look at fs/read_write.c and
.\" the function signatures that do:
.\" ..., unsigned long, pos_l, unsigned long, pos_h, ...
.\" If they use off_t, then they most likely do not belong in this list.
This does not affect syscalls that manually split and assemble 64\-bit values
such as \fB_llseek\fP(2), \fBpreadv\fP(2), \fBpreadv2\fP(2), \fBpwritev\fP(2), and
\fBpwritev2\fP(2).  Welcome to the wonderful world of historical baggage.
.SS アーキテクチャー毎の呼び出し規約
各アーキテクチャーには、それぞれ独自のシステムコール起動方法とカーネルへの引数の渡し方がある。 各種のアーキテクチャーの詳細を以下の 2
つの表にまとめる。
.PP
The first table lists the instruction used to transition to kernel mode
(which might not be the fastest or best way to transition to the kernel, so
you might have to refer to \fBvdso\fP(7)), the register used to indicate the
system call number, the register(s) used to return the system call result,
and the register used to signal an error.
.if  t \{\
.ft CW
\}
.TS
l2	l2	l2	l2	l1	l2	l.
 Arch/ABI	Instruction	System	Ret	Ret	Error	備考
		call #	val	val2
_
alpha	callsys	v0	v0	a4	a3	1, 6
arc	trap0	r8	r0	\-	\-
arm/OABI	swi NR	\-	r0	\-	\-	 2
arm/EABI	swi 0x0	r7	r0	r1	\-
arm64	svc #0	w8	x0	x1	\-
blackfin	excpt 0x0	P0	R0	\-	\-
i386	int $0x80	eax	eax	edx	\-
ia64	break 0x100000	r15	r8	r9	r10	1, 6
m68k	trap #0	d0	d0	\-	\-
microblaze	brki r14,8	 r12	r3	\-	\-
mips	syscall	v0	v0	v1	a3	1, 6
nios2	trap	r2	r2	\-	r7
parisc	ble 0x100(%sr2, %r0)	r20	r28	\-	\-
powerpc	sc	r0	r3	\-	r0	 1
powerpc64	sc	r0	r3	\-	cr0.SO	 1
 riscv	 ecall	 a7	a0	a1	\-
s390	svc 0	r1	r2	r3	\-	 3
s390x	svc 0	r1	r2	r3	\-	 3
superh	trap #0x17	r3	r0	r1	\-	4, 6
sparc/32	t 0x10	g1	o0	o1	psr/csr	1, 6
sparc/64	t 0x6d	g1	o0	o1	psr/csr	1, 6
tile	swint1	 R10	 R00	\-	 R01	 1
x86\-64	syscall	rax	rax	rdx	\-	 5
 x32	syscall	rax	rax	rdx	\-	 5
xtensa	syscall	a2	a2	\-	\-
.TE
.PP
Notes:
.IP [1] 4
On a few architectures, a register is used as a boolean (0 indicating no
error, and \-1 indicating an error) to signal that the system call failed.
The actual error value is still contained in the return register.  On sparc,
the carry bit (\fIcsr\fP)  in the processor status register (\fIpsr\fP)  is used
instead of a full register.  On powerpc64, the summary overflow bit (\fISO\fP)
in field 0 of the condition register (\fIcr0\fP)  is used.
.IP [2]
\fINR\fP is the system call number.
.IP [3]
s390 と s390x では、 \fINR\fP (システムコール番号) が 256 未満の場合 \fIsvc\ NR\fP で NR が直接渡される場合がある。
.IP [4]
On SuperH, the trap number controls the maximum number of arguments passed.
A \fItrap\ #0x10\fP can be used with only 0\-argument system calls, a \fItrap\ #0x11\fP can be used with 0\- or 1\-argument system calls, and so on up to
\fItrap #0x17\fP for 7\-argument system calls.
.IP [5]
The x32 ABI shares syscall table with x86\-64 ABI, but there are some
nuances:
.RS
.IP \(bu 3
In order to indicate that a system call is called under the x32 ABI, an
additional bit, \fB__X32_SYSCALL_BIT\fP, is bitwise\-ORed with the system call
number.  The ABI used by a process affects some process behaviors, including
signal handling or system call restarting.
.IP \(bu
Since x32 has different sizes for \fIlong\fP and pointer types, layouts of some
(but not all; \fIstruct timeval\fP or \fIstruct rlimit\fP are 64\-bit, for example)
structures are different.  In order to handle this, additional system calls
are added to the system call table, starting from number 512 (without the
\fB__X32_SYSCALL_BIT\fP).  For example, \fB__NR_readv\fP is defined as 19 for the
x86\-64 ABI and as \fI__X32_SYSCALL_BIT\fP | \fB515\fP for the x32 ABI.  Most of
these additional system calls are actually identical to the system calls
used for providing i386 compat.  There are some notable exceptions, however,
such as \fBpreadv2\fP(2), which uses \fIstruct iovec\fP entities with 4\-byte
pointers and sizes ("compat_iovec" in kernel terms), but passes an 8\-byte
\fIpos\fP argument in a single register and not two, as is done in every other
ABI.
.RE
.IP [6]
Some architectures (namely, Alpha, IA\-64, MIPS, SuperH, sparc/32, and
sparc/64)  use an additional register ("Retval2" in the above table)  to
pass back a second return value from the \fBpipe\fP(2)  system call; Alpha uses
this technique in the architecture\-specific \fBgetxpid\fP(2), \fBgetxuid\fP(2),
and \fBgetxgid\fP(2)  system calls as well.  Other architectures do not use the
second return value register in the system call interface, even if it is
defined in the System V ABI.
.if  t \{\
.in
.ft P
\}
.PP
2 つ目の表は、システムコールの引数を渡すのに使用されるレジスターの一覧である。
.if  t \{\
.ft CW
\}
.TS
l	l2	l2	l2	l2	l2	l2	l2	l.
 Arch/ABI	arg1	arg2	arg3	arg4	arg5	arg6	arg7	備考
_
alpha	a0	a1	a2	a3	a4	a5	\-
arc	r0	r1	r2	r3	r4	r5	\-
arm/OABI	r0	r1	r2	r3	r4	r5	r6
arm/EABI	r0	r1	r2	r3	r4	r5	r6
arm64	x0	x1	x2	x3	x4	x5	\-
blackfin	R0	R1	R2	R3	R4	R5	\-
i386	ebx	ecx	edx	esi	edi	ebp	\-
ia64	out0	out1	out2	out3	out4	out5	\-
m68k	d1	d2	d3	d4	d5	a0	\-
microblaze	r5	r6	r7	r8	r9	r10	\-
mips/o32	a0	a1	a2	a3	\-	\-	\-	 1
mips/n32,64	a0	a1	a2	a3	a4	a5	\-
nios2	r4	r5	r6	r7	r8	r9	\-
parisc	r26	r25	r24	r23	r22	r21	\-
powerpc	r3	r4	r5	r6	r7	r8	r9
powerpc64	r3	r4	r5	r6	r7	r8	\-
 riscv	a0	a1	a2	a3	a4	a5	\-
s390	r2	r3	r4	r5	r6	r7	\-
s390x	r2	r3	r4	r5	r6	r7	\-
superh	r4	r5	r6	r7	r0	r1	r2
sparc/32	o0	o1	o2	o3	o4	o5	\-
sparc/64	o0	o1	o2	o3	o4	o5	\-
tile	 R00	 R01	 R02	 R03	 R04	 R05	\-
x86\-64	rdi	rsi	rdx	r10	r8	r9	\-
 x32	rdi	rsi	rdx	r10	r8	r9	\-
xtensa	 a6	a3	a4	a5	a8	a9	\-
.TE
.PP
Notes:
.IP [1] 4
mips/o32 のシステムコールの規約では、 ユーザースタックに引数を 5 個から 8 個渡す。
.if  t \{\
.in
.ft P
\}
.PP
これらの表にはすべての呼び出し規約が記載されているわけではない点に注意すること \(em
アーキテクチャーによっては、ここに記載されていない他のレジスターが見境なく上書きされる場合もある。
.SH 例
.EX
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <signal.h>

int
main(int argc, char *argv[])
{
    pid_t tid;

     tid = syscall(SYS_gettid);
    syscall(SYS_tgkill, getpid(), tid, SIGHUP);
}
.EE
.SH 関連項目
\fB_syscall\fP(2), \fBintro\fP(2), \fBsyscalls\fP(2), \fBerrno\fP(3), \fBvdso\fP(7)
.SH この文書について
この man ページは Linux \fIman\-pages\fP プロジェクトのリリース 5.10 の一部である。プロジェクトの説明とバグ報告に関する情報は
\%https://www.kernel.org/doc/man\-pages/ に書かれている。