DOCSLIB.ORG

Linux System Calls for HLA Programmers

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Linux System Calls for HLA Programmers Linux System Calls Linux System Calls for HLA Programmers 1 Introduction This document describes the interface between HLA and Linux via direct system calls. The HLA Standard Library provides a header file with a set of important constants, data types, and procedure prototypes that you can use to make Linux system calls. Unlike the "C Standard Library," the HLA-based systems calls add very little overhead to a system call (generally, they move parameters into registers and invoke Linux with very little other processing). Note that I have copied information from the Linux man pages into this document. So whatever copyright (copy- left) applies to that information applies here as well. As far as I am concerned, my work on this document is public domain, so this document inherits the Linux documentation copyright (I don’t know the details, but it’s probably the "Free Documentation" license; whatever it is, it applies equally here). Note that Linux man pages are known to contain some misinformation. That misinformation was copied straight through to this document. Of course, in a document of this size, there are probably some defects I’ve introduced as well, so keep this in mind when using this document. Disclaimer: I would like to claim that every effort has been taken to ensure the accuracy of the material appearing within this document. That, however, would be a complete lie. In reality, I copied the man pages to this document and make a bunch of quick changes for HLA/assembly programmers to their descriptions. Undoubtedly, this process has introduced additional defects into the descriptions. Therefore, if something doesn’t seem right or doesn’t seem to work properly, it’s probably due to an error in this documentation. Keep this in mind when using this document. Hopefully as time passes and this document matures, many of the defects will disappear. Also note that (as this was begin written) I have not had time to completely test every system call, constant, and wrapper function provided with HLA. If you’re having a problem with a system call, be sure to check out the HLA source code for the Linux wrapper functions and whatever constants and data types you’re using from the linux.hhf module. 1.1 Direct System Calls from Assembly Language To invoke a Linux system call (i.e., a Linux API call), you load parameters into various registers, load a system call opcode into the EAX register, and execute an INT($80) instruction. Linux returns results in the EAX register and, possibly, via certain pass by reference parameters. The HLA "linux.hhf" header file contains constant declarations for most of the Linux system call opcodes. These constants take the form "sys_function" where function represents a Linux system call name. For example, "sys_exit" is the symbolic name for the Linux "_exit" call (this constant just happens to have the value one). If you read the on-line documentation for the Linux system calls, you’ll find that the API calls are specified using a "C" language syntax. However, it’s very easy to convert the C examples to assembly language. Just load the associ- ated system call constant into EAX and then load the 80x86 registers with the following values: • 1st parameter: EBX • 2nd parameter: ECX • 3rd parameter: EDX • 4th parameter: ESI • 5th parameter: EDI Certain Linux 2.4 calls pass a sixth parameter in EBP. Calls compatible with earlier versions of the kernel pass six or more parameters in a parameter block and pass the address of the parameter block in EBX (this change was probably made in kernel 2.4 because someone noticed that an extra copy between kernel and user space was slowing down those functions with exactly six parameters; who knows the real reason, though). As an example, consiider the Linux exit system call. This has a "C" prototype similar to the following: void exit( int returnCode ); The assembly invocation of this function takes the following form: Released to the Public Domain by Randall Hyde Page 1 Linux System Calls mov( sys_exit, eax ); mov( returnCode, ebx ); int( $80 ); As you can see, calls to Linux are very similar to BIOS or DOS calls on the PC (for those of you who are familiar with such system calls). While it is certainly possible for you to load the system call parameters directly into the 80x86 registers, load a system call "opcode" into EAX, and execute an INT($80) instruction directly, this is a lot of work if your program makes several Linux system calls. To make life easier for assembly programmers, the Linux system call module provided with the HLA Standard Library provides wrapper functions that make Linux system calls a lot more convenient. These are functions that let you pass parameters on the stack (using the HLA high level procedure call syntax) which is much more convenient than loading the registers and execut- ing INT($80). For example, consider the following implementation of the "linux._exit" function the Linux module provides: procedure _exit( RtnCode: dword ); @nodisplay; begin _exit; mov( sys_exit, eax ); mov( RtnCode, ebx ); int( $80 ); end _exit; You can call this function using the HLA syntax: linux._exit( returnValue ); As you can see, this is far more convenient to use than the INT($80) sequence given earlier. Furthermore, this calling sequence is very similar to the "C" syntax, so it should be very familiar to those reading Linux documentation (which is based on "C"). Your code would probably be slightly smaller and a tiny bit faster if you directly make the INT($80) calls.. However, since the transition from user space to kernel space is very expensive, the few extra cycles needed to pass the parameters on the stack to the HLA functions is nearly meaningless. In a typical (large) program, the memory savings would probably be measured in hundreds of bytes, if not less. So you’re not really going to gain much by making the INT($80) calls. Since the HLA code is much more convenient to use, you really should call the Standard Library functions. For those who are concerned about inefficiencies, here’s what a typical HLA Standard Library Linux system call looks like. As you can see, there’s not much to these functions. So you shouldn’t worry at all about efficiency loss. On occasion, certain Linux system calls become obsolete. Linux has maintained the calls for the older functions for those programs that require the old semantics, while adding new API calls that support addi- tional features. A classic example is the LSEEK and LLSEEK functions. Originally, there was only LSEEK (that only supports two gigabyte file lengths). Linux added the LLSEEK function to allow access to larger files. Still, the old LSEEK function exists for code that was written prior to the development of the LLSEEK call. So if you use the INT($80) mechanism to invoke Linux, you probably don’t have to worry too much about certain system calls disappearing on you. There is, however, a big advantage to using the HLA wrapper functions. If you use the INT($80) call- ing mechanism and a system call becomes obsolete, your program will probably still work but it won’t be able to take advantage of the new Linux features within your program without rewriting the affected INT($80) calls. On the other hand, if you call the HLA wrappers, this problem exists in only one place -- in the HLA Standard Library wrapper functions. This means that whenever the Linux system calls change, you need only modify the affected wrapper function (typically in one place), recompile the HLA Standard Library, recompile your applications, and you’re in business. This is much easier than attempting to locate every INT($80) call in your code and checking to see if you need to change it. Combined with the ease of calling the HLA wrapper functions, you should serious consider whether it’s worth it to call Linux via INT($80). For this reason, the remainder of this document will assume that you’re using the HLA Linux Page 2 Version: 4/5/02 Written by Randall Hyde Linux System Calls module to call the Linux APIs. If you choose to use the INT($80) calling mechanism instead, conversion is fairly trivial (as noted above). 1.2 A Quick Note About Naming Conventions Most Linux documentation was written assuming that the reader would be calling Linux from a C/C++ program. While the HLA header files (and this document) attempt to stick as closely to the original Linux names as possible, there are a few areas where HLA names deviate from the C names. This can occur for any of three reasons: • The C name conflicts with an HLA reserved word (e.g., "exit" becomes "_exit" because "exit" is an HLA reserved word). • C uses different namespaces for structs and other objects and some Linux identifiers are the same for both structs and variables (HLA doesn’t allow this). • HLA uses case neutral identifiers, C uses case sensitive identifiers. Therefore, if two C identifiers are the same except for alphabetic case, one of them must be changed when converting to HLA. • Many Linux constant and macro declarations use the (stylistically dubious) convention of all uppercase characters. Since uppercase is hard to read, such identifiers have been converted to all lowercase in the HLA header files. 1.3 A Quick Note About Error Return Values C/C++ programmers probably expect Linux system calls to return -1 if an error occurs and then they expect to find the actual error code in the errno global variable.
Load more

Recommended publications
  • Better Performance Through a Disk/Persistent-RAM Hybrid Design
    The Conquest File System: Better Performance Through a Disk/Persistent-RAM Hybrid Design AN-I ANDY WANG Florida State University GEOFF KUENNING Harvey Mudd College PETER REIHER, GERALD POPEK University of California, Los Angeles ________________________________________________________________________ Modern file systems assume the use of disk, a system-wide performance bottleneck for over a decade. Current disk caching and RAM file systems either impose high overhead to access memory content or fail to provide mechanisms to achieve data persistence across reboots. The Conquest file system is based on the observation that memory is becoming inexpensive, which enables all file system services to be delivered from memory, except providing large storage capacity. Unlike caching, Conquest uses memory with battery backup as persistent storage, and provides specialized and separate data paths to memory and disk. Therefore, the memory data path contains no disk-related complexity. The disk data path consists of only optimizations for the specialized disk usage pattern. Compared to a memory-based file system, Conquest incurs little performance overhead. Compared to several disk-based file systems, Conquest achieves 1.3x to 19x faster memory performance, and 1.4x to 2.0x faster performance when exercising both memory and disk. Conquest realizes most of the benefits of persistent RAM at a fraction of the cost of a RAM-only solution. Conquest also demonstrates that disk-related optimizations impose high overheads for accessing memory content in a memory-rich environment. Categories and Subject Descriptors: D.4.2 [Operating Systems]: Storage Management—Storage Hierarchies; D.4.3 [Operating Systems]: File System Management—Access Methods and Directory Structures; D.4.8 [Operating Systems]: Performance—Measurements General Terms: Design, Experimentation, Measurement, and Performance Additional Key Words and Phrases: Persistent RAM, File Systems, Storage Management, and Performance Measurement ________________________________________________________________________ 1.
    [Show full text]
  • System Calls System Calls
    System calls We will investigate several issues related to system calls. Read chapter 12 of the book Linux system call categories file management process management error handling note that these categories are loosely defined and much is behind included, e.g. communication. Why? 1 System calls File management system call hierarchy you may not see some topics as part of “file management”, e.g., sockets 2 System calls Process management system call hierarchy 3 System calls Error handling hierarchy 4 Error Handling Anything can fail! System calls are no exception Try to read a file that does not exist! Error number: errno every process contains a global variable errno errno is set to 0 when process is created when error occurs errno is set to a specific code associated with the error cause trying to open file that does not exist sets errno to 2 5 Error Handling error constants are defined in errno.h here are the first few of errno.h on OS X 10.6.4 #define EPERM 1 /* Operation not permitted */ #define ENOENT 2 /* No such file or directory */ #define ESRCH 3 /* No such process */ #define EINTR 4 /* Interrupted system call */ #define EIO 5 /* Input/output error */ #define ENXIO 6 /* Device not configured */ #define E2BIG 7 /* Argument list too long */ #define ENOEXEC 8 /* Exec format error */ #define EBADF 9 /* Bad file descriptor */ #define ECHILD 10 /* No child processes */ #define EDEADLK 11 /* Resource deadlock avoided */ 6 Error Handling common mistake for displaying errno from Linux errno man page: 7 Error Handling Description of the perror () system call.
    [Show full text]
  • File Formats
    man pages section 4: File Formats Sun Microsystems, Inc. 4150 Network Circle Santa Clara, CA 95054 U.S.A. Part No: 817–3945–10 September 2004 Copyright 2004 Sun Microsystems, Inc. 4150 Network Circle, Santa Clara, CA 95054 U.S.A. All rights reserved. This product or document is protected by copyright and distributed under licenses restricting its use, copying, distribution, and decompilation. No part of this product or document may be reproduced in any form by any means without prior written authorization of Sun and its licensors, if any. Third-party software, including font technology, is copyrighted and licensed from Sun suppliers. Parts of the product may be derived from Berkeley BSD systems, licensed from the University of California. UNIX is a registered trademark in the U.S. and other countries, exclusively licensed through X/Open Company, Ltd. Sun, Sun Microsystems, the Sun logo, docs.sun.com, AnswerBook, AnswerBook2, and Solaris are trademarks or registered trademarks of Sun Microsystems, Inc. in the U.S. and other countries. All SPARC trademarks are used under license and are trademarks or registered trademarks of SPARC International, Inc. in the U.S. and other countries. Products bearing SPARC trademarks are based upon an architecture developed by Sun Microsystems, Inc. The OPEN LOOK and Sun™ Graphical User Interface was developed by Sun Microsystems, Inc. for its users and licensees. Sun acknowledges the pioneering efforts of Xerox in researching and developing the concept of visual or graphical user interfaces for the computer industry. Sun holds a non-exclusive license from Xerox to the Xerox Graphical User Interface, which license also covers Sun’s licensees who implement OPEN LOOK GUIs and otherwise comply with Sun’s written license agreements.
    [Show full text]
  • System Calls
    System Calls What are they? ● Standard interface to allow the kernel to safely handle user requests – Read from hardware – Spawn a new process – Get current time – Create shared memory ● Message passing technique between – OS kernel (server) – User (client) Executing System Calls ● User program issues call ● Core kernel looks up call in syscall table ● Kernel module handles syscall action ● Module returns result of system call ● Core kernel forwards result to user Module is not Loaded... ● User program issues call ● Core kernel looks up call in syscall table ● Kernel module isn't loaded to handle action ● ... ● Where does call go? System Call Wrappers ● Wrapper calls system call if loaded – Otherwise returns an error ● Needs to be in a separate location so that the function can actually be called – Uses function pointer to point to kernel module implementation Adding System Calls ● You'll need to add and implement: – int start_elevator(void); – int issue_request(int, int, int); – int stop_elevator(void); ● As an example, let's add a call to printk an argument passed in: – int test_call(int); Adding System Calls ● Files to add (project files): – /usr/src/test_kernel/hello_world/test_call.c – /usr/src/test_kernel/hello_world/hello.c – /usr/src/test_kernel/hello_world/Makefile ● Files to modify (core kernel): – /usr/src/test_kernel/arch/x86/entry/syscalls/syscall_64.tbl – /usr/src/test_kernel/include/linux/syscalls.h – /usr/src/test_kernel/Makefile hello_world/test_call.c ● #include <linux/linkage.h> ● #include <linux/kernel.h> ● #include
    [Show full text]
  • Life in the Fast Lane: Optimisation for Interactive and Batch Jobs Nikola Marković, Boemska T.S
    Paper 11825-2016 Life in the Fast Lane: Optimisation for Interactive and Batch Jobs Nikola Marković, Boemska T.S. Ltd.; Greg Nelson, ThotWave Technologies LLC. ABSTRACT We spend so much time talking about GRID environments, distributed jobs, and huge data volumes that we ignore the thousands of relatively tiny programs scheduled to run every night, which produce only a few small data sets, but make all the difference to the users who depend on them. Individually, these jobs might place a negligible load on the system, but by their sheer number they can often account for a substantial share of overall resources, sometimes even impacting the performance of the bigger, more important jobs. SAS® programs, by their varied nature, use available resources in a varied way. Depending on whether a SAS® procedure is CPU-, disk- or memory-intensive, chunks of memory or CPU can sometimes remain unused for quite a while. Bigger jobs leave bigger chunks, and this is where being small and able to effectively exploit those leftovers can be a great advantage. We call our main optimization technique the Fast Lane, which is a queue configuration dedicated to jobs with consistently small SASWORK directories, that, when available, lets them use unused RAM in place of their SASWORK disk. The approach improves overall CPU saturation considerably while taking loads off the I/O subsystem, and without failure results in improved runtimes for big jobs and small jobs alike, without requiring any changes to deployed code. This paper explores the practical aspects of implementing the Fast Lane on your environment.
    [Show full text]
  • Programming Project 5: User-Level Processes
    Project 5 Operating Systems Programming Project 5: User-Level Processes Due Date: ______________________________ Project Duration: One week Overview and Goal In this project, you will explore user-level processes. You will create a single process, running in its own address space. When this user-level process executes, the CPU will be in “user mode.” The user-level process will make system calls to the kernel, which will cause the CPU to switch into “system mode.” Upon completion, the CPU will switch back to user mode before resuming execution of the user-level process. The user-level process will execute in its own “logical address space.” Its address space will be broken into a number of “pages” and each page will be stored in a frame in memory. The pages will be resident (i.e., stored in frames in physical memory) at all times and will not be swapped out to disk in this project. (Contrast this with “virtual” memory, in which some pages may not be resident in memory.) The kernel will be entirely protected from the user-level program; nothing the user-level program does can crash the kernel. Download New Files The files for this project are available in: http://www.cs.pdx.edu/~harry/Blitz/OSProject/p5/ Please retain your old files from previous projects and don’t modify them once you submit them. You should get the following files: Switch.s Runtime.s System.h System.c Page 1 Project 5 Operating Systems List.h List.c BitMap.h BitMap.c makefile FileStuff.h FileStuff.c Main.h Main.c DISK UserRuntime.s UserSystem.h UserSystem.c MyProgram.h MyProgram.c TestProgram1.h TestProgram1.c TestProgram2.h TestProgram2.c The following files are unchanged from the last project and you should not modify them: Switch.s Runtime.s System.h System.c -- except HEAP_SIZE has been modified List.h List.c BitMap.h BitMap.c The following files are not provided; instead you will modify what you created in the last project.
    [Show full text]
  • Winreporter Documentation
    WinReporter documentation Table Of Contents 1.1 WinReporter overview ............................................................................................... 1 1.1.1.................................................................................................................................... 1 1.1.2 Web site support................................................................................................. 1 1.2 Requirements.............................................................................................................. 1 1.3 License ....................................................................................................................... 1 2.1 Welcome to WinReporter........................................................................................... 2 2.2 Scan requirements ...................................................................................................... 2 2.3 Simplified Wizard ...................................................................................................... 3 2.3.1 Simplified Wizard .............................................................................................. 3 2.3.2 Computer selection............................................................................................. 3 2.3.3 Validate .............................................................................................................. 4 2.4 Advanced Wizard....................................................................................................... 5 2.4.1
    [Show full text]
  • 007-2007: the FILENAME Statement Revisited
    SAS Global Forum 2007 Applications Development Paper 007-2007 The FILENAME Statement Revisited Yves DeGuire, Statistics Canada, Ottawa, Ontario, Canada ABSTRACT The FILENAME statement has been around for a long time for connecting external files with SAS®. Over the years, it has grown quite a bit to encompass capabilities that go beyond the simple sequential file. Most SAS programmers have used the FILENAME statement to read/write external files stored on disk. However, few programmers have used it to access devices other than disk or to interface with different access methods. This paper focuses on some of those capabilities by showing you some interesting devices and access methods supported by the FILENAME statement. INTRODUCTION – FILENAME STATEMENT 101 The FILENAME statement is a declarative statement that is used to associate a fileref with a physical file or a device. A fileref is a logical name that can be used subsequently in lieu of a physical name. The syntax for the FILENAME statement is as follows: FILENAME fileref <device-type> <'external-file'> <options>; This is the basic syntax to associate an external file or a device to a fileref. There are other forms that allow you to list or clear filerefs. Please refer to SAS OnlineDoc® documentation for a complete syntax of the FILENAME statement. Once the association has been made between a physical file and a fileref, the fileref can be used in as many DATA steps as necessary without having to re-run a FILENAME statement. Within a DATA step, the use of an INFILE or a FILE statement allows the programmer to determine which file to read or write using an INPUT or a PUT statement.
    [Show full text]
  • Files and Processes (Review)
    Files and Processes (review) Files and Processes (review) 1/61 Learning Objectives Files and Processes (review) I Review of files in standard C versus using system call interface for files I Review of buffering concepts I Review of process memory model I Review of bootup sequence in Linux and Microsoft Windows I Review of basic system calls under Linux: fork, exec, wait, exit, sleep, alarm, kill, signal I Review of similar basic system calls under MS Windows 2/61 Files Files and I Recall how we write a file copy program in standard C. Processes (review) #include <stdio.h> FILE *fopen(const char *path, const char *mode); size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); int fclose(FILE *fp); I We can also use character-based functions such as: #include <stdio.h> int fgetc(FILE *stream); int fputc(int c, FILE *stream); I With either approach, we can write a C program that will work on any operating system as it is in standard C. 3/61 Standard C File Copy Files and Processes (review) I Uses fread and fwrite. I files-processes/stdc-mycp.c 4/61 POSIX/Unix Files Files and Processes (review) I "On a UNIX system, everything is a file; if something is not a file, it is a process." I A directory is just a file containing names of other files. I Programs, services, texts, images, and so forth, are all files. I Input and output devices, and generally all devices, are considered to be files.
    [Show full text]
  • The Application of File Identification, Validation, and Characterization Tools in Digital Curation
    THE APPLICATION OF FILE IDENTIFICATION, VALIDATION, AND CHARACTERIZATION TOOLS IN DIGITAL CURATION BY KEVIN MICHAEL FORD THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Library and Information Science in the Graduate College of the University of Illinois at Urbana-Champaign, 2011 Urbana, Illinois Advisers: Research Assistant Professor Melissa Cragin Assistant Professor Jerome McDonough ABSTRACT File format identification, characterization, and validation are considered essential processes for digital preservation and, by extension, long-term data curation. These actions are performed on data objects by humans or computers, in an attempt to identify the type of a given file, derive characterizing information that is specific to the file, and validate that the given file conforms to its type specification. The present research reviews the literature surrounding these digital preservation activities, including their theoretical basis and the publications that accompanied the formal release of tools and services designed in response to their theoretical foundation. It also reports the results from extensive tests designed to evaluate the coverage of some of the software tools developed to perform file format identification, characterization, and validation actions. Tests of these tools demonstrate that more work is needed – particularly in terms of scalable solutions – to address the expanse of digital data to be preserved and curated. The breadth of file types these tools are anticipated to handle is so great as to call into question whether a scalable solution is feasible, and, more broadly, whether such efforts will offer a meaningful return on investment. Also, these tools, which serve to provide a type of baseline reading of a file in a repository, can be easily tricked.
    [Show full text]
  • Chapter 10: File System
    Chapter 10: File System Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne © 2013 Chapter 10: File System File Concept Access Methods Disk and Directory Structure File-System Mounting File Sharing Protection Operating System Concepts – 9th Edition 11.2 Silberschatz, Galvin and Gagne © 2013 Objectives To explain the function of file systems To describe the interfaces to file systems To discuss file-system design tradeoffs, including access methods, file sharing, file locking, and directory structures To explore file-system protection Operating System Concepts – 9th Edition 11.3 Silberschatz, Galvin and Gagne © 2013 File Concept Contiguous logical address space Types: Data numeric character binary Program Contents defined by file’s creator Many types Consider text file, source file, executable file Operating System Concepts – 9th Edition 11.4 Silberschatz, Galvin and Gagne © 2013 File Structure None - sequence of words, bytes Simple record structure Lines Fixed length Variable length Complex Structures Formatted document Relocatable load file Can simulate last two with first method by inserting appropriate control characters Who decides: Operating system Program Operating System Concepts – 9th Edition 11.5 Silberschatz, Galvin and Gagne © 2013 File Attributes Name – only information kept in human-readable form Identifier – unique tag (number) identifies file within file system Type – needed for systems that support different types Location – pointer to file location on device Size
    [Show full text]
  • Man Pages Section 2 System Calls
    man pages section 2: System Calls Part No: E29032 October 2012 Copyright © 1993, 2012, Oracle and/or its affiliates. All rights reserved. This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited. The information contained herein is subject to change without notice and is not warranted to be error-free. If you find any errors, please report them to us in writing. If this is software or related documentation that is delivered to the U.S. Government or anyone licensing it on behalf of the U.S. Government, the following notice is applicable: U.S. GOVERNMENT END USERS. Oracle programs, including any operating system, integrated software, any programs installed on the hardware, and/or documentation, delivered to U.S. Government end users are "commercial computer software" pursuant to the applicable Federal Acquisition Regulation and agency-specific supplemental regulations. As such, use, duplication, disclosure, modification, and adaptation of the programs, including anyoperating system, integrated software, any programs installed on the hardware, and/or documentation, shall be subject to license terms and license restrictions applicable to the programs. No other rights are granted to the U.S. Government. This software or hardware is developed for general use in a variety of information management applications.
    [Show full text]