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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">System call</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="System_command" class="mw-redirect" title="System command">System command</a>.</div>

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<p>In computing, a <b>system call</b> (<b>syscall</b>) is the programmatic way in which a <a href="Computer_program" title="Computer program">computer program</a> requests a service from the <a href="Operating_system" title="Operating system">operating system</a><sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>a<span class="cite-bracket">]</span></a></sup> on which it is executed. This may include hardware-related services (for example, accessing a <a href="Hard_disk_drive" title="Hard disk drive">hard disk drive</a> or accessing the device's camera), creation and execution of new <a href="Process_(computing)" title="Process (computing)">processes</a>, and communication with integral <a href="Kernel_service" class="mw-redirect" title="Kernel service">kernel services</a> such as <a href="Process_scheduling" class="mw-redirect" title="Process scheduling">process scheduling</a>. System calls provide an essential interface between a process and the operating system.

</p><p>In most systems, system calls can only be made from <a href="Userspace" class="mw-redirect" title="Userspace">userspace</a> processes, while in some systems, <a href="OS/360_and_successors" title="OS/360 and successors">OS/360 and successors</a> for example, privileged system code also issues system calls.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>For <a href="Embedded_system" title="Embedded system">embedded systems</a>, system calls typically do not change the <a href="CPU_modes" title="CPU modes">privilege mode</a> of the CPU.

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<div class="mw-heading mw-heading2"><h2 id="Privileges">Privileges</h2></div>

<p>The <a href="Instruction_set" class="mw-redirect" title="Instruction set">architecture</a> of most modern processors, with the exception of some embedded systems, involves a <a href="CPU_modes" title="CPU modes">security model</a>. For example, the <i><a href="Ring_(computer_security)" class="mw-redirect" title="Ring (computer security)">rings</a></i> model specifies multiple privilege levels under which software may be executed: a program is usually limited to its own <a href="Address_space" title="Address space">address space</a> so that it cannot access or modify other running programs or the operating system itself, and is usually prevented from directly manipulating hardware devices (e.g. the <a href="Frame_buffer" class="mw-redirect" title="Frame buffer">frame buffer</a> or <a href="Computer_network" title="Computer network">network</a> devices).

</p><p>However, many applications need access to these components, so system calls are made available by the operating system to provide well-defined, safe implementations for such operations. The operating system executes at the highest level of privilege, and allows applications to request services via system calls, which are often initiated via <a href="Interrupt" title="Interrupt">interrupts</a>. An interrupt automatically puts the CPU into some elevated privilege level and then passes control to the kernel, which determines whether the calling program should be granted the requested service. If the service is granted, the kernel executes a specific set of instructions over which the calling program has no direct control, returns the privilege level to that of the calling program, and then returns control to the calling program.

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<div class="mw-heading mw-heading2"><h2 id="The_library_as_an_intermediary">The library as an intermediary</h2></div>

<p>Generally, systems provide a <a href="Library_(computing)" title="Library (computing)">library</a> or <a href="API" title="API">API</a> that sits between normal programs and the operating system. On <a href="Unix-like" title="Unix-like">Unix-like</a> systems, that API is usually part of an implementation of the <a href="C_standard_library" title="C standard library">C library</a> (libc), such as <a href="Glibc" title="Glibc">glibc</a>, that provides <a href="Wrapper_function" title="Wrapper function">wrapper functions</a> for the system calls, often named the same as the system calls they invoke. On <a href="Windows_NT" title="Windows NT">Windows NT</a>, that API is part of the <a href="Native_API" class="mw-redirect" title="Native API">Native API</a>, in the <style data-mw-deduplicate="TemplateStyles:r886049734">

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</style><span class="monospaced">ntdll.dll</span> library; this is an undocumented API used by implementations of the regular <a href="Windows_API" title="Windows API">Windows API</a> and directly used by some system programs on Windows. The library's wrapper functions expose an ordinary function <a href="Calling_convention" title="Calling convention">calling convention</a> (a <a href="Subroutine" class="mw-redirect" title="Subroutine">subroutine</a> call on the <a href="Assembly_language" title="Assembly language">assembly</a> level) for using the system call, as well as making the system call more <a href="Modularity" title="Modularity">modular</a>. Here, the primary function of the wrapper is to place all the arguments to be passed to the system call in the appropriate <a href="Processor_register" title="Processor register">processor registers</a> (and maybe on the <a href="Call_stack" title="Call stack">call stack</a> as well), and also setting a unique system call number for the kernel to call. In this way the library, which exists between the OS and the application, increases <a href="Software_portability" title="Software portability">portability</a>.

</p><p>The call to the library function itself does not cause a switch to <a href="Kernel_mode" class="mw-redirect" title="Kernel mode">kernel mode</a> and is usually a normal <a href="Subroutine_call" class="mw-redirect" title="Subroutine call">subroutine call</a> (using, for example, a "CALL" assembly instruction in some <a href="Instruction_set_architecture" title="Instruction set architecture">Instruction set architectures</a> (ISAs)). The actual system call does transfer control to the kernel (and is more implementation-dependent and platform-dependent than the library call abstracting it). For example, in <a href="Unix-like" title="Unix-like">Unix-like</a> systems, <code>fork</code> and <code>execve</code> are C library functions that in turn execute instructions that invoke the <code>fork</code> and <code>exec</code> system calls. Making the system call directly in the <a href="Application_code" class="mw-redirect" title="Application code">application code</a> is more complicated and may require embedded assembly code to be used (in <a href="C_(programming_language)" title="C (programming language)">C</a> and <a href="C%2B%2B" title="C++">C++</a>), as well as requiring knowledge of the low-level binary interface for the system call operation, which may be subject to change over time and thus not be part of the <a href="Application_binary_interface" title="Application binary interface">application binary interface</a>; the library functions are meant to abstract this away.

</p><p>On <a href="Exokernel" title="Exokernel">exokernel</a> based systems, the library is especially important as an intermediary. On exokernels, libraries shield user applications from the very low level kernel <a href="Application_programming_interface" class="mw-redirect" title="Application programming interface">API</a>, and provide <a href="Abstraction_(computer_science)" title="Abstraction (computer science)">abstractions</a> and <a href="Resource_(computer_science)" class="mw-redirect" title="Resource (computer science)">resource</a> management.

</p><p>IBM's <a href="OS/360_and_successors" title="OS/360 and successors">OS/360</a>, <a href="DOS/360_and_successors" title="DOS/360 and successors">DOS/360</a> and <a href="TSS/360" class="mw-redirect" title="TSS/360">TSS/360</a> implement most system calls through a library of assembly language <a href="Macro_(computer_science)" title="Macro (computer science)">macros</a>,<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>b<span class="cite-bracket">]</span></a></sup> although there are a few services with a call linkage. This reflects their origin at a time when programming in assembly language was more common than <a href="High-level_programming_language" title="High-level programming language">high-level language</a> usage. IBM system calls were therefore not directly executable by high-level language programs, but required a callable assembly language wrapper subroutine. Since then, IBM has added many services that can be called from high level languages in, e.g., <a href="Z/OS" title="Z/OS">z/OS</a> and <a href="VSE_(operating_system)" title="VSE (operating system)">z/VSE</a>. In more recent release of <a href="MVS/SP" class="mw-redirect" title="MVS/SP">MVS/SP</a> and in all later MVS versions, some system call macros generate Program Call (PC).

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<div class="mw-heading mw-heading2"><h2 id="Examples_and_tools">Examples and tools</h2></div>

<p>On <a href="Unix" title="Unix">Unix</a>, <a href="Unix-like" title="Unix-like">Unix-like</a> and other <a href="POSIX" title="POSIX">POSIX</a>-compliant operating systems, popular system calls are <code><a href="Open_(system_call)" title="Open (system call)">open</a></code>, <code><a href="Read_(system_call)" title="Read (system call)">read</a></code>, <code><a href="Write_(system_call)" title="Write (system call)">write</a></code>, <code><a href="Close_(system_call)" title="Close (system call)">close</a></code>, <code><a href="Wait_(system_call)" title="Wait (system call)">wait</a></code>, <code><a href="Exec_(system_call)" title="Exec (system call)">exec</a></code>, <code><a href="Fork_(system_call)" title="Fork (system call)">fork</a></code>, <code><a href="Exit_(system_call)" title="Exit (system call)">exit</a></code>, and <code><a href="Kill_(system_call)" class="mw-redirect" title="Kill (system call)">kill</a></code>. Many modern operating systems have hundreds of system calls. For example, <a href="Linux_kernel" title="Linux kernel">Linux</a> and <a href="OpenBSD" title="OpenBSD">OpenBSD</a> each have over 300 different calls,<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> <a href="NetBSD" title="NetBSD">NetBSD</a> has close to 500,<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> <a href="FreeBSD" title="FreeBSD">FreeBSD</a> has over 500,<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Windows has close to 2000, divided between win32k (graphical) and ntdll (core) system calls<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> while <a href="Plan_9_from_Bell_Labs" title="Plan 9 from Bell Labs">Plan 9</a> has 54.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p><p>Tools such as <a href="Strace" title="Strace">strace</a>, <a href="Ftrace" title="Ftrace">ftrace</a> and truss allow a process to execute from start and report all system calls the process invokes, or can attach to an already running process and intercept any system call made by the said process if the operation does not violate the permissions of the user. This special ability of the program is usually also implemented with system calls such as <a href="Ptrace" title="Ptrace">ptrace</a> or system calls on files in <a href="Procfs" title="Procfs">procfs</a>.

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<div class="mw-heading mw-heading2"><h2 id="Typical_implementations">Typical implementations</h2></div>

<p>Implementing system calls requires a transfer of control from user space to kernel space, which involves some sort of architecture-specific feature. A typical way to implement this is to use a <a href="Software_interrupt" class="mw-redirect" title="Software interrupt">software interrupt</a> or <a href="Trap_(computing)" class="mw-redirect" title="Trap (computing)">trap</a>. Interrupts transfer control to the operating system <a href="Kernel_(operating_system)" title="Kernel (operating system)">kernel</a>, so software simply needs to set up some register with the system call number needed, and execute the software interrupt.

</p><p>This is the only technique provided for many <a href="RISC" class="mw-redirect" title="RISC">RISC</a> processors, but <a href="Complex_instruction_set_computer" title="Complex instruction set computer">CISC</a> architectures such as <a href="X86" title="X86">x86</a> support additional techniques. For example, the x86 <a href="Instruction_set" class="mw-redirect" title="Instruction set">instruction set</a> contains the instructions <code>SYSCALL</code>/<code>SYSRET</code> and <code>SYSENTER</code>/<code>SYSEXIT</code> (these two mechanisms were independently created by <a href="AMD" title="AMD">AMD</a> and <a href="Intel" title="Intel">Intel</a>, respectively, but in essence they do the same thing). These are "fast" control transfer instructions that are designed to quickly transfer control to the kernel for a system call without the overhead of an interrupt.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> <a href="Linux" title="Linux">Linux</a> 2.5 began using this on the <a href="X86" title="X86">x86</a>, where available; formerly it used the <code><a href="INT_(x86_instruction)" title="INT (x86 instruction)">INT</a></code> instruction, where the system call number was placed in the <code>EAX</code> <a href="Processor_register" title="Processor register">register</a> before <a href="INT_(x86_instruction)" title="INT (x86 instruction)">interrupt</a> 0x80 was executed.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup>

</p><p>An older mechanism is the <a href="Call_gate" class="mw-redirect" title="Call gate">call gate</a>; originally used in <a href="Multics" title="Multics">Multics</a> and later, for example, see <a href="Call_gate_(Intel)" title="Call gate (Intel)">call gate</a> on the Intel <a href="X86" title="X86">x86</a>. It allows a program to call a kernel function directly using a safe control transfer mechanism, which the operating system sets up in advance. This approach has been unpopular on x86, presumably due to the requirement of a far call (a call to a procedure located in a different segment than the current code segment<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup>) which uses <a href="X86_memory_segmentation" title="X86 memory segmentation">x86 memory segmentation</a> and the resulting lack of <a href="Portability_(software)" class="mw-redirect" title="Portability (software)">portability</a> it causes, and the existence of the faster instructions mentioned above.

</p><p>For <a href="IA-64" title="IA-64">IA-64</a> architecture, <code>EPC</code> (Enter Privileged Code) instruction is used. The first eight system call arguments are passed in registers, and the rest are passed on the stack.

</p><p>In the <a href="IBM_System/360" title="IBM System/360">IBM System/360</a> mainframe family, and its successors, a <a href="Supervisor_Call_instruction" title="Supervisor Call instruction">Supervisor Call instruction</a> (<span class="monospaced">SVC</span>), with the number in the instruction rather than in a register, implements a system call for legacy facilities in most of<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>c<span class="cite-bracket">]</span></a></sup> IBM's own operating systems, and for all system calls in Linux. In later versions of MVS, IBM uses the Program Call (PC) instruction for many newer facilities. In particular, PC is used when the caller might be in <a href="Service_Request_Block" title="Service Request Block">Service Request Block</a> (SRB) mode.

</p><p>The <a href="PDP-11" title="PDP-11">PDP-11</a> <a href="Minicomputer" title="Minicomputer">minicomputer</a> used the <span class="monospaced">EMT</span>, <span class="monospaced">TRAP</span> and <span class="monospaced">IOT</span> instructions, which, similar to the IBM System/360 <span class="monospaced">SVC</span> and x86 <span class="monospaced">INT</span>, put the code in the instruction; they generate interrupts to specific addresses, transferring control to the operating system. The <a href="VAX" title="VAX">VAX</a> 32-bit successor to the PDP-11 series used the <span class="monospaced">CHMK</span>, <span class="monospaced">CHME</span>, and <span class="monospaced">CHMS</span> instructions to make system calls to privileged code at various levels; the code is an argument to the instruction.

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<div class="mw-heading mw-heading2"><h2 id="Categories_of_system_calls">Categories of system calls</h2></div>

<p>System calls can be grouped roughly into six major categories:<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup>

</p>

<ol><li>Process control

<ul><li>create process (for example, <code><a href="Fork_(system_call)" title="Fork (system call)">fork</a></code> on Unix-like systems, or <code>NtCreateProcess</code> in the <a href="Windows_NT" title="Windows NT">Windows NT</a> <a href="Native_API" class="mw-redirect" title="Native API">Native API</a>)</li>

<li><a href="Kill_(command)" title="Kill (command)">terminate process</a></li>

<li><a href="Loader_(computing)" title="Loader (computing)">load</a>, <a href="Exec_(system_call)" title="Exec (system call)">execute</a></li>

<li>get/set process attributes</li>

<li><a href="Wait_(system_call)" title="Wait (system call)">wait</a> for time, wait event, <a href="Signal_(IPC)" title="Signal (IPC)">signal</a> event</li>

<li><a href="Memory_allocation" class="mw-redirect" title="Memory allocation">allocate</a> and <a href="Garbage_collection_(computer_science)" title="Garbage collection (computer science)">free</a> memory</li></ul></li>

<li>File management

<ul><li>create file, delete file</li>

<li>open, close</li>

<li>read, write, reposition</li>

<li>get/set file attributes</li></ul></li>

<li>Device management

<ul><li>request device, release device</li>

<li>read, write, reposition</li>

<li>get/set device attributes</li>

<li>logically attach or detach devices</li></ul></li>

<li>Information maintenance

<ul><li>get/set total system information (including time, date, computer name, enterprise etc.)</li>

<li>get/set process, file, or device metadata (including author, opener, creation time and date, etc.)</li></ul></li>

<li>Communication

<ul><li>create, delete communication connection</li>

<li>send, receive messages</li>

<li>transfer status information</li>

<li>attach or detach remote devices</li></ul></li>

<li>Protection

<ul><li>get/set file permissions</li></ul></li></ol>

<div class="mw-heading mw-heading2"><h2 id="Processor_mode_and_context_switching">Processor mode and context switching</h2></div>

<p>System calls in most <a href="Unix-like" title="Unix-like">Unix-like</a> systems are processed in <a href="Kernel_mode" class="mw-redirect" title="Kernel mode">kernel mode</a>, which is accomplished by changing the processor execution mode to a more privileged one, but no <i>process</i> <a href="Context_switch" title="Context switch">context switch</a> is necessary – although a <i>privilege</i> context switch does occur. The hardware sees the world in terms of the execution mode according to the processor <a href="Status_register" title="Status register">status register</a>, and processes are an abstraction provided by the operating system. A system call does not generally require a context switch to another process; instead, it is processed in the context of whichever process invoked it.<sup id="cite_ref-Bach1986pp15-16_16-0" class="reference"><a href="#cite_note-Bach1986pp15-16-16"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup>

</p><p>In a <a href="Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">multithreaded</a> process, system calls can be made from multiple <a href="Thread_(computing)" title="Thread (computing)">threads</a>. The handling of such calls is dependent on the design of the specific operating system kernel and the application runtime environment. The following list shows typical models followed by operating systems:<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li><i>Many-to-one</i> model: All system calls from any user thread in a process are handled by a single kernel-level thread. This model has a serious drawback – any blocking system call (like awaiting input from the user) can freeze all the other threads. Also, since only one thread can access the kernel at a time, this model cannot utilize multiple cores of processors.</li>

<li><i>One-to-one</i> model: Every user thread gets attached to a distinct kernel-level thread during a system call. This model solves the above problem of blocking system calls. It is found in all major <a href="Linux_distribution" title="Linux distribution">Linux distributions</a>, <a href="MacOS" title="MacOS">macOS</a>, <a href="IOS" title="IOS">iOS</a>, recent <a href="Microsoft_Windows" title="Microsoft Windows">Windows</a> and <a href="Solaris_(operating_system)" class="mw-redirect" title="Solaris (operating system)">Solaris</a> versions.</li>

<li><i>Many-to-many</i> model: In this model, a pool of user threads is mapped to a pool of kernel threads. All system calls from a user thread pool are handled by the threads in their corresponding kernel <a href="Thread_pool" title="Thread pool">thread pool</a>.</li>

<li><i>Hybrid</i> model: This model implements both many-to-many and one-to-one models depending upon the choice made by the kernel. This is found in old versions of <a href="IRIX" title="IRIX">IRIX</a>, <a href="HP-UX" title="HP-UX">HP-UX</a> and <a href="Solaris_(operating_system)" class="mw-redirect" title="Solaris (operating system)">Solaris</a>.</li></ul>

<li><a href="Linux_kernel_API" class="mw-redirect" title="Linux kernel API">Linux kernel API</a></li>

<div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">In <a href="UNIX-like" class="mw-redirect" title="UNIX-like">UNIX-like</a> operating systems, system calls are used only for the <a href="Kernel_(operating_system)" title="Kernel (operating system)">kernel</a>.</span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">In many but not all cases, IBM documented, e.g., the SVC number, the parameter registers.</span>

</li>

<li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text">The CP components of <a href="CP-67" title="CP-67">CP-67</a> and <a href="VM_(operating_system)" title="VM (operating system)">VM</a> use the Diagnose (DIAG) instruction as a Hypervisor CALL (HVC) from a virtual machine to CP.</span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFIBM1967" class="citation book cs1">IBM (March 1967). "Writing SVC Routines". <a rel="nofollow" class="external text" href="http://bitsavers.org/pdf/ibm/360/os/R01-08/C28-6550-2_OSsysPrmg_Mar67.pdf"><i>IBM System/360 Operating System System Programmer's Guide</i></a> <span class="cs1-format">(PDF)</span>. Third Edition. pp. <span class="nowrap">32–</span>36. C28-6550-2.</cite></span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://man7.org/linux/man-pages/man2/syscalls.2.html">"syscalls(2) - Linux manual page"</a>.</cite></span>

</li>

<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><cite id="CITEREFOpenBSD2013" class="citation web cs1">OpenBSD (14 September 2013). <a rel="nofollow" class="external text" href="http://bxr.su/OpenBSD/sys/kern/syscalls.c">"System call names (kern/syscalls.c)"</a>. <i>BSD Cross Reference</i>.</cite></span>

</li>

<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><cite id="CITEREFNetBSD2013" class="citation web cs1">NetBSD (17 October 2013). <a rel="nofollow" class="external text" href="http://bxr.su/NetBSD/sys/kern/syscalls.c">"System call names (kern/syscalls.c)"</a>. <i>BSD Cross Reference</i>.</cite></span>

</li>

<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://fxr.watson.org/fxr/source/kern/syscalls.c">"FreeBSD syscalls.c, the list of syscall names and IDs"</a>.</cite></span>

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<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><cite id="CITEREFMateusz_"j00ru"_Jurczyk2017" class="citation web cs1">Mateusz "j00ru" Jurczyk (5 November 2017). <a rel="nofollow" class="external text" href="http://j00ru.vexillium.org/syscalls/win32k/32/">"Windows WIN32K.SYS System Call Table (NT/2000/XP/2003/Vista/2008/7/8/10)"</a>.</cite><span class="cs1-maint citation-comment"><code class="cs1-code">{{cite web}}</code>: CS1 maint: numeric names: authors list (link)</span></span>

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<li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://9p.io/sources/plan9/sys/src/libc/9syscall/sys.h">"sys.h"</a>. <i>Plan 9 from Bell Labs</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20230908211500/http://9p.io/sources/plan9/sys/src/libc/9syscall/sys.h">Archived</a> from the original on 8 September 2023,</cite> the list of syscall names and IDs.</span>

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<li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://wiki.osdev.org/SYSENTER">"SYSENTER"</a>. <i>OSDev wiki</i>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20231108202438/https://wiki.osdev.org/Sysenter">Archived</a> from the original on 8 November 2023.</cite></span>

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<li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><cite id="CITEREFAnonymous2002" class="citation web cs1">Anonymous (19 December 2002). <a rel="nofollow" class="external text" href="http://kerneltrap.org/node/531">"Linux 2.5 gets vsyscalls, sysenter support"</a>. <i><a href="KernelTrap" title="KernelTrap">KernelTrap</a></i><span class="reference-accessdate">. Retrieved <span class="nowrap">1 January</span> 2008</span>.</cite></span>

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<li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><cite id="CITEREFManu_Garg2006" class="citation web cs1">Manu Garg (2006). <a rel="nofollow" class="external text" href="http://articles.manugarg.com/systemcallinlinux2_6.html">"Sysenter Based System Call Mechanism in Linux 2.6"</a>.</cite></span>

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<li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://x86.renejeschke.de/html/file_module_x86_id_26.html">"Liberation: x86 Instruction Set Reference"</a>. <i>renejeschke.de</i><span class="reference-accessdate">. Retrieved <span class="nowrap">4 July</span> 2015</span>.</cite></span>

</li>

<li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><cite id="CITEREFSilberschatz2018" class="citation book cs1">Silberschatz, Abraham (2018). <i>Operating System Concepts</i>. Peter B Galvin; Greg Gagne (10th ed.). Hoboken, NJ: Wiley. p. 67. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9781119320913</bdi>. <a href="OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/1004849022">1004849022</a>.</cite></span>

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<li id="cite_note-Bach1986pp15-16-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-Bach1986pp15-16_16-0">^</a></b></span> <span class="reference-text">Bach, Maurice J. (1986), <i>The Design of the UNIX Operating System</i>, Prentice Hall, pp. 15–16.</span>

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<li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><cite id="CITEREFElliot2011" class="citation web cs1">Elliot, John (2011). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120724153438/https://www.progclub.org/pipermail/list/2011-October/000150.html">"Discussion of system call implementation at ProgClub including quote from Bach 1986"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.progclub.org/pipermail/list/2011-October/000150.html">the original</a> on 24 July 2012<span class="reference-accessdate">. Retrieved <span class="nowrap">1 October</span> 2011</span>.</cite></span>

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<li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/4_Threads.html">"Threads"</a>.</cite></span>

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<li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://kevinmarquet.net/wp-content/uploads/threading.pdf">"Threading Models"</a> <span class="cs1-format">(PDF)</span>.</cite></span>

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</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://fxr.watson.org/fxr/source/kern/syscalls.master">A list of modern Unix-like system calls</a></li>

<li><a rel="nofollow" class="external text" href="https://archive.today/20121220032539/http://www.makelinux.net/kernel_map/">Interactive Linux kernel map</a> with main API functions and structures, <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180827040646/http://www.makelinux.net/kernel_map/LKM.pdf">PDF</a> version</li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20051024081539/http://docs.cs.up.ac.za/programming/asm/derick_tut/syscalls.html">Linux system calls</a> – system calls for <a href="Linux_kernel" title="Linux kernel">Linux kernel</a> 2.2, with <a href="IA-32" title="IA-32">IA-32</a> <a href="Calling_convention" title="Calling convention">calling conventions</a></li>

<li><a rel="nofollow" class="external text" href="http://www.tldp.org/LDP/khg/HyperNews/get/syscall/syscall86.html">How System Calls Work on Linux/i86</a> (1996, based on the 1993 0.99.2 kernel)</li>

<li><a rel="nofollow" class="external text" href="http://articles.manugarg.com/systemcallinlinux2_6.html">Sysenter Based System Call Mechanism in Linux 2.6</a> (2006)</li>

<li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20170211232040/https://www.ibm.com/developerworks/linux/library/l-system-calls/">"Kernel command using Linux system calls"</a>. <i>IBM developerWorks</i>. 10 February 2010. Archived from <a rel="nofollow" class="external text" href="https://www.ibm.com/developerworks/linux/library/l-system-calls/">the original</a> on 11 February 2017.</cite></li>

<li>Choudhary, Amit; <a rel="nofollow" class="external text" href="http://tldp.org/HOWTO/html_single/Implement-Sys-Call-Linux-2.6-i386">HOWTO for Implementing a System Call on Linux 2.6</a></li>

<li>Jorrit N. Herder, Herbert Bos, Ben Gras, Philip Homburg, and Andrew S. Tanenbaum, <a rel="nofollow" class="external text" href="https://www.usenix.org/publications/login/april-2006-volume-31-number-2/modular-system-programming-minix-3">Modular system programming on Minix 3</a>, <i>;login:</i> 31, no. 2 (April 2006); 19–28, accessed 5 March 2018</li>

<li><a rel="nofollow" class="external text" href="http://task3.cc/projects/bd-shell/">A simple open Unix Shell in C language</a> – examples on System Calls under Unix</li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20121224002314/http://netcode.cz/img/83/nativeapi.html">Inside the Native API</a> – <a href="Windows_NT" title="Windows NT">Windows NT</a> <a href="Native_API" class="mw-redirect" title="Native API">Native API</a>, including system calls</li>

<li>Gulbrandsen, John; <a rel="nofollow" class="external text" href="http://www.codeguru.com/cpp/misc/misc/system/article.php/c8223/System-Call-Optimization-with-the-SYSENTER-Instruction.htm"><i>System Call Optimization with the SYSENTER Instruction</i></a>, CodeGuru.com, 8 October 2004</li>

<li><a rel="nofollow" class="external text" href="https://wiki.osdev.org/System_Calls">osdev wiki</a></li></ul>

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</style><div id="Application_binary_interface_(ABI)74" style="font-size:114%;margin:0 4em"><a href="Application_binary_interface" title="Application binary interface">Application binary interface</a> (ABI)</div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Parts,<br>conventions</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Data_structure_alignment" title="Data structure alignment">Alignment</a></li>

<li><a href="Calling_convention" title="Calling convention">Calling convention</a></li>

<li><a href="Call_stack" title="Call stack">Call stack</a></li>

<li><a href="Library_(computing)" title="Library (computing)">Library</a>

<ul><li><a href="Static_library" title="Static library">static</a></li></ul></li>

<li><a href="Machine_code" title="Machine code">Machine code</a></li>

<li><a href="Memory_segmentation" title="Memory segmentation">Memory segmentation</a></li>

<li><a href="Name_mangling" title="Name mangling">Name mangling</a></li>

<li><a href="Object_code" title="Object code">Object code</a></li>

<li><a href="Opaque_pointer" title="Opaque pointer">Opaque pointer</a></li>

<li><a href="Position-independent_code" title="Position-independent code">Position-independent code</a></li>

<li><a href="Relocation_(computing)" title="Relocation (computing)">Relocation</a></li>

<li><a href="Virtual_method_table" title="Virtual method table">Virtual method table</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Binary-code_compatibility" title="Binary-code compatibility">Binary-code compatibility</a></li>

<li><a href="Foreign_function_interface" title="Foreign function interface">Foreign function interface</a></li>

<li><a href="Language_binding" title="Language binding">Language binding</a></li>

<li><a href="Linker_(computing)" title="Linker (computing)">Linker</a>

<ul><li><a href="Dynamic_linker" title="Dynamic linker">dynamic</a></li></ul></li>

<li><a href="Loader_(computing)" title="Loader (computing)">Loader</a></li>

<li><a href="Year_2038_problem" title="Year 2038 problem">Year 2038 problem</a></li></ul>

</div></td></tr></tbody></table></div></div><div><div class="zim-footer">

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