.\" 2015-01-17, Kees Cook <keescook@chromium.org>
.\" Added mips and arm64.
.\"
-.TH SYSCALL 2 2017-03-13 "Linux" "Linux Programmer's Manual"
+.TH SYSCALL 2 2020-02-09 "Linux" "Linux Programmer's Manual"
.SH NAME
syscall \- indirect system call
.SH SYNOPSIS
.nf
-.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
.B #include <unistd.h>
.BR "#include <sys/syscall.h> " "/* For SYS_xxx definitions */"
-
+.PP
.BI "long syscall(long " number ", ...);"
.fi
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.BR syscall ():
+.PD 0
+.ad l
+.RS 4
+.TP 4
+Since glibc 2.19:
+_DEFAULT_SOURCE
+.TP
+Before glibc 2.19:
+_BSD_SOURCE || _SVID_SOURCE
+.RE
+.ad
+.PD
.SH DESCRIPTION
.BR syscall ()
is a small library function that invokes
.BR syscall ()
is useful, for example,
when invoking a system call that has no wrapper function in the C library.
-
+.PP
.BR syscall ()
saves CPU registers before making the system call,
restores the registers upon return from the system call,
and stores any error code returned by the system call in
.BR errno (3)
if an error occurs.
-
+.PP
Symbolic constants for system call numbers can be found in the header file
.IR <sys/syscall.h> .
.SH RETURN VALUE
to make a system call,
the caller might need to handle architecture-dependent details;
this requirement is most commonly encountered on certain 32-bit architectures.
-
+.PP
For example, on the ARM architecture Embedded ABI (EABI), a
64-bit value (e.g.,
.IR "long long" )
.BR readahead ()
system call would be invoked as follows on the ARM architecture with the EABI
in little endian mode:
-
+.PP
.in +4n
-.nf
+.EX
syscall(SYS_readahead, fd, 0,
(unsigned int) (offset & 0xFFFFFFFF),
(unsigned int) (offset >> 32),
count);
-.fi
+.EE
.in
.PP
Since the offset argument is 64 bits, and the first argument
(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
Similar issues can occur on MIPS with the O32 ABI,
-on PowerPC with the 32-bit ABI, and on Xtensa.
+on PowerPC and parisc with the 32-bit ABI, and on Xtensa.
.\" Mike Frysinger: this issue ends up forcing MIPS
.\" O32 to take 7 arguments to syscall()
-
+.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 userspace.
-
+it uses a shim layer to hide the issue from user space.
+.PP
The affected system calls are
.BR fadvise64_64 (2),
.BR ftruncate64 (2),
.BR sync_file_range (2),
and
.BR truncate64 (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:
.BR _llseek (2),
.BR preadv (2),
.BR preadv2 (2),
-.BR pwritev (2).
+.BR pwritev (2),
and
.BR pwritev2 (2).
Welcome to the wonderful world of historical baggage.
Every architecture has its own way of invoking and passing arguments to the
kernel.
The details for various architectures are listed in the two tables below.
-
+.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
.BR vdso (7)),
the register used to indicate the system call number,
-the register used to return the system call result,
+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 l2 l.
-arch/ABI instruction syscall # retval error Notes
+l2 l2 l2 l2 l1 l2 l.
+Arch/ABI Instruction System Ret Ret Error Notes
+ call # val val2
_
-alpha callsys v0 a0 a3 [1]
-arc trap0 r8 r0 -
-arm/OABI swi NR - a1 - [2]
-arm/EABI swi 0x0 r7 r0 -
-arm64 svc #0 x8 x0 -
-blackfin excpt 0x0 P0 R0 -
-i386 int $0x80 eax eax -
-ia64 break 0x100000 r15 r8 r10 [1]
-m68k trap #0 d0 d0 -
-microblaze brki r14,8 r12 r3 -
-mips syscall v0 v0 a3 [1]
-nios2 trap r2 r2 r7
-parisc ble 0x100(%sr2, %r0) r20 r28 -
-powerpc sc r0 r3 r0 [1]
-s390 svc 0 r1 r2 - [3]
-s390x svc 0 r1 r2 - [3]
-superh trap #0x17 r3 r0 - [4]
-sparc/32 t 0x10 g1 o0 psr/csr [1]
-sparc/64 t 0x6d g1 o0 psr/csr [1]
-tile swint1 R10 R00 R01 [1]
-x86_64 syscall rax rax - [5]
-x32 syscall rax rax - [5]
-xtensa syscall a2 a2 -
+alpha callsys v0 v0 a4 a3 1, 6
+arc trap0 r8 r0 - -
+arm/OABI swi NR - a1 - - 2
+arm/EABI swi 0x0 r7 r0 r1 -
+arm64 svc #0 x8 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:
-.RS 4
.IP [1] 4
On a few architectures,
a register is used as a boolean
in the processor status register
.RI ( psr )
is used instead of a full register.
+On powerpc64, the summary overflow bit
+.RI ( SO )
+in field 0 of the condition register
+.RI ( cr0 )
+is used.
.IP [2]
.I NR
is the system call number.
.IR "trap #0x17"
for 7-argument system calls.
.IP [5]
-The x32 ABI uses the same instruction as the x86_64 ABI and is used on
-the same processors.
-To differentiate between them, the bit mask
-.I __X32_SYSCALL_BIT
-is bitwise-ORed into the system call number for system calls
-under the x32 ABI.
-Both system call tables are available though,
-so setting the bit is not a hard requirement.
+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,
+.BR __X32_SYSCALL_BIT ,
+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
+.I long
+and pointer types, layouts of some (but not all;
+.I struct timeval
+or
+.I struct rlimit
+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
+.BR __X32_SYSCALL_BIT ).
+For example,
+.B __NR_readv
+is defined as 19 for the x86-64 ABI and as
+.IR __X32_SYSCALL_BIT " | " \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
+.BR preadv2 (2),
+which uses
+.I struct iovec
+entities with 4-byte pointers and sizes ("compat_iovec" in kernel terms),
+but passes an 8-byte
+.I pos
+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
+.BR pipe (2)
+system call;
+Alpha uses this technique in the architecture-specific
+.BR getxpid (2),
+.BR getxuid (2),
+and
+.BR getxgid (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
\}
.TS
l l2 l2 l2 l2 l2 l2 l2 l.
-arch/ABI arg1 arg2 arg3 arg4 arg5 arg6 arg7 Notes
+Arch/ABI arg1 arg2 arg3 arg4 arg5 arg6 arg7 Notes
_
alpha a0 a1 a2 a3 a4 a5 -
arc r0 r1 r2 r3 r4 r5 -
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/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 -
+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:
-.RS 4
.IP [1] 4
The mips/o32 system call convention passes
arguments 5 through 8 on the user stack.
-.RE
.if t \{\
.in
.ft P
Note that these tables don't cover the entire calling convention\(emsome
architectures may indiscriminately clobber other registers not listed here.
.SH EXAMPLE
-.nf
+.EX
#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
tid = syscall(SYS_gettid);
syscall(SYS_tgkill, getpid(), tid, SIGHUP);
}
-.fi
+.EE
.SH SEE ALSO
.BR _syscall (2),
.BR intro (2),
projects / thirdparty / man-pages.git / blobdiff