Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 368 insertions, 0 deletions

diff --git a/man/man2/syscall.2 b/man/man2/syscall.2
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+'\" t
+.\" Copyright (c) 1980, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" SPDX-License-Identifier: BSD-4-Clause-UC
+.\"
+.\"     @(#)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.
+.\"
+.TH syscall 2 2024-05-02 "Linux man-pages (unreleased)"
+.SH NAME
+syscall \- indirect system call
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
+.B #include <unistd.h>
+.P
+.BI "long syscall(long " number ", ...);"
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR syscall ():
+.nf
+    Since glibc 2.19:
+        _DEFAULT_SOURCE
+    Before glibc 2.19:
+        _BSD_SOURCE || _SVID_SOURCE
+.fi
+.SH DESCRIPTION
+.BR syscall ()
+is a small library function that invokes
+the system call whose assembly language
+interface has the specified
+.I number
+with the specified arguments.
+Employing
+.BR syscall ()
+is useful, for example,
+when invoking a system call that has no wrapper function in the C library.
+.P
+.BR syscall ()
+saves CPU registers before making the system call,
+restores the registers upon return from the system call,
+and stores any error returned by the system call in
+.BR errno (3).
+.P
+Symbolic constants for system call numbers can be found in the header file
+.IR <sys/syscall.h> .
+.SH RETURN VALUE
+The return value is defined by the system call being invoked.
+In general, a 0 return value indicates success.
+A \-1 return value indicates an error,
+and an error number is stored in
+.IR errno .
+.SH ERRORS
+.TP
+.B ENOSYS
+The requested system call number is not implemented.
+.P
+Other errors are specific to the invoked system call.
+.SH NOTES
+.BR syscall ()
+first appeared in
+4BSD.
+.SS Architecture-specific requirements
+Each architecture ABI has its own requirements on how
+system call arguments are passed to the kernel.
+For system calls that have a glibc wrapper (e.g., most system calls),
+glibc handles the details of copying arguments to the right registers
+in a manner suitable for the architecture.
+However, when using
+.BR syscall ()
+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.
+.P
+For example, on the ARM architecture Embedded ABI (EABI), a
+64-bit value (e.g.,
+.IR "long long" )
+must be aligned to an even register pair.
+Thus, using
+.BR syscall ()
+instead of the wrapper provided by glibc,
+the
+.BR readahead (2)
+system call would be invoked as follows on the ARM architecture with the EABI
+in little endian mode:
+.P
+.in +4n
+.EX
+syscall(SYS_readahead, fd, 0,
+        (unsigned int) (offset & 0xFFFFFFFF),
+        (unsigned int) (offset >> 32),
+        count);
+.EE
+.in
+.P
+Since the offset argument is 64 bits, and the first argument
+.RI ( fd )
+is passed in
+.IR r0 ,
+the caller must manually split and align the 64-bit value
+so that it is passed in the
+.IR r2 / r3
+register pair.
+That means inserting a dummy value into
+.I r1
+(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).
+.P
+Similar issues can occur on MIPS with the O32 ABI,
+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()
+.P
+.\" 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.
+.P
+The affected system calls are
+.BR fadvise64_64 (2),
+.BR ftruncate64 (2),
+.BR posix_fadvise (2),
+.BR pread64 (2),
+.BR pwrite64 (2),
+.BR readahead (2),
+.BR sync_file_range (2),
+and
+.BR truncate64 (2).
+.P
+.\" 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
+.BR _llseek (2),
+.BR preadv (2),
+.BR preadv2 (2),
+.BR pwritev (2),
+and
+.BR pwritev2 (2).
+Welcome to the wonderful world of historical baggage.
+.SS Architecture calling conventions
+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.
+.P
+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(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	Notes
+		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
+loongarch	syscall 0	a7	a0	-	-
+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	trapa #31	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
+.P
+Notes:
+.IP \[bu] 3
+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
+.RI ( csr )
+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 \[bu]
+.I NR
+is the system call number.
+.IP \[bu]
+For s390 and s390x,
+.I NR
+(the system call number) may be passed directly with
+.I "svc\ NR"
+if it is less than 256.
+.IP \[bu]
+On SuperH additional trap numbers are supported for historic reasons, but
+.BR trapa #31
+is the recommended "unified" ABI.
+.IP \[bu]
+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 \[bu]
+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
+\}
+.P
+The second table shows the registers used to pass the system call arguments.
+.if t \{\
+.ft CW
+\}
+.TS
+l	l2	l2	l2	l2	l2	l2	l2	l.
+Arch/ABI	arg1	arg2	arg3	arg4	arg5	arg6	arg7	Notes
+_
+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	-
+loongarch	a0	a1	a2	a3	a4	a5	a6
+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
+.P
+Notes:
+.IP \[bu] 3
+The mips/o32 system call convention passes
+arguments 5 through 8 on the user stack.
+.if t \{\
+.in
+.ft P
+\}
+.P
+Note that these tables don't cover the entire calling convention\[em]some
+architectures may indiscriminately clobber other registers not listed here.
+.SH EXAMPLES
+.\" SRC BEGIN (syscall.c)
+.EX
+#define _GNU_SOURCE
+#include <signal.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
+\&
+int
+main(void)
+{
+    pid_t tid;
+\&
+    tid = syscall(SYS_gettid);
+    syscall(SYS_tgkill, getpid(), tid, SIGHUP);
+}
+.EE
+.\" SRC END
+.SH SEE ALSO
+.BR _syscall (2),
+.BR intro (2),
+.BR syscalls (2),
+.BR errno (3),
+.BR vdso (7)