COMP 3000 Lab 3 2012 - Revision history

Afry: /* Answers */

2012-11-13T17:50:25Z

Answers

← Older revision		Revision as of 17:50, 13 November 2012
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	== Answers ==		== Answers ==
	<ol>		<ol>
	<li> __libc_start_main		<li> __libc_start_main getpid()
	__printf_chk </li>		__printf_chk </li>

Soma at 03:40, 5 November 2012

2012-11-05T03:40:59Z

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 </pre>
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 <li>NI is the static priority of the process - its "niceness" value.  This value can be increased (= priority lowered) by an unprivileged user for their processes using the renice command or the nice system call.  (The nice command is used to start a process with a given priority.)  The root user can decrease the niceness value as well (increasing the process's priority).  The PR column is the process's dynamic priority, a value used by the scheduler to determine which process should run next.  The PR value is a function a process's static priority (the NI value) and its recent execution history (is it waiting for I/O, has it used a lot of CPU time, etc).
 </ol>

Soma: /* Answers */

2012-11-05T03:25:36Z

Answers

← Older revision		Revision as of 03:25, 5 November 2012
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	<li>Note that your program cannot do anything after the SEGV signal is handled as the invalid pointer will just be accessed again. There does exist libraries for allowing SEGV to be handled (e.g., libsigsegv), but this is in general for userspace virtual memory management.		<li>Note that your program cannot do anything after the SEGV signal is handled as the invalid pointer will just be accessed again. There does exist libraries for allowing SEGV to be handled (e.g., libsigsegv), but this is in general for userspace virtual memory management.
	<pre>		<pre>
	/* ~~receive-term~~.c */		/* nocrash.c */

	~~/* To test handler, run killall -s SIGTERM receive-term~~ */

	#include <unistd.h>		#include <unistd.h>

Soma: /* Answers */

2012-11-05T03:24:46Z

Answers

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+}
 </pre>
-<li>
+<li>Note that your program cannot do anything after the SEGV signal is handled as the invalid pointer will just be accessed again.  There does exist libraries for allowing SEGV to be handled (e.g., libsigsegv), but this is in general for userspace virtual memory management.
 <li>
 <li>NI is the static priority of the process - its "niceness" value.  This value can be increased (= priority lowered) by an unprivileged user for their processes using the renice command or the nice system call.  (The nice command is used to start a process with a given priority.)  The root user can decrease the niceness value as well (increasing the process's priority).  The PR column is the process's dynamic priority, a value used by the scheduler to determine which process should run next.  The PR value is a function a process's static priority (the NI value) and its recent execution history (is it waiting for I/O, has it used a lot of CPU time, etc).
 </ol>

Soma: /* Answers */

2012-11-05T02:30:51Z

Answers

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+}
 </pre>
-<li>
+<li><pre>
 <li>
 <li>
 <li>NI is the static priority of the process - its "niceness" value.  This value can be increased (= priority lowered) by an unprivileged user for their processes using the renice command or the nice system call.  (The nice command is used to start a process with a given priority.)  The root user can decrease the niceness value as well (increasing the process's priority).  The PR column is the process's dynamic priority, a value used by the scheduler to determine which process should run next.  The PR value is a function a process's static priority (the NI value) and its recent execution history (is it waiting for I/O, has it used a lot of CPU time, etc).
 </ol>

Soma: /* Answers */

2012-11-04T21:27:33Z

Answers

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+}
 </pre>
-<li>
+<li><pre>
 <li>
 <li>

Soma: /* Answers */

2012-11-04T20:57:18Z

Answers

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 <li>Operating systems open files to 1) establish a mapping between a pathname and the contents of the file so that the pathname doesn't have to be parsed on every file access, and 2) so the OS can allocate resources (particularly buffers) to accelerate access to the file.  Those buffers can be released (and data flushed to disk) when the file is closed.
 <li>Library calls are function calls, just to functions stored in dynamic libraries that are "included" with the system.  (Note that what is included or not is an ambiguous concept in most Linux distributions.)  System calls are invocations of the kernel (typically via a software interrupt).  A system call's functionality is typically implemented by C functions; because the kernel must run in supervisor mode and regular programs run in user mode, regular function calls don't work between them.  Indeed, userspace programs cannot even directly access the memory of the kernel for security reasons; that is why system calls must be vectored via software interrupts.
-<li>
+<li><pre>
 <li>
 <li>

Soma: /* Part B */

2012-11-04T20:55:19Z

Part B

← Older revision		Revision as of 20:55, 4 November 2012
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	<li value=9> [2] Why do we "open" files? Specifically, to what extent is it possible to do file I/O without open and close operations - assuming you could change the UNIX API?		<li value=9> [2] Why do we "open" files? Specifically, to what extent is it possible to do file I/O without open and close operations - assuming you could change the UNIX API?
	<li> [2] What is the relationship between function calls, system calls, and library calls?		<li> [2] What is the relationship between function calls, system calls, and library calls?
	<li> [2] Create ''run-program-skips.c'' that is the same as run-program.c except that it ignores every other argument to the program to be run (starting with the first non-program-name argument). Hence, ''./run-program-~~skip~~ /bin/ls ignore -a ignore /tmp'' will do the same as ''./run-program /bin/ls -a /tmp''. </li>		<li> [2] Create ''run-program-skips.c'' that is the same as run-program.c except that it ignores every other argument to the program to be run (starting with the first non-program-name argument). Hence, ''./run-program-skips /bin/ls ignore -a ignore /tmp'' will do the same as ''./run-program /bin/ls -a /tmp''. </li>
	<li> [2] Create ''sanitize-env.c'' that does the same as run-program.c except it exec's the program with all environment variables stripped except the PATH and TERM variables (assuming they are defined). Be sure to document how you tested your program.		<li> [2] Create ''sanitize-env.c'' that does the same as run-program.c except it exec's the program with all environment variables stripped except the PATH and TERM variables (assuming they are defined). Be sure to document how you tested your program.
	<li> [2] Create a simple program ''receive-term.c'' that uses sigaction in order to print "Ouch!" when you send the program the TERM signal and then exits. Note that your program should not consume much CPU time while waiting (i.e., do not poll for the signal). As part of your answer, give the command for sending the signal.</li>		<li> [2] Create a simple program ''receive-term.c'' that uses sigaction in order to print "Ouch!" when you send the program the TERM signal and then exits. Note that your program should not consume much CPU time while waiting (i.e., do not poll for the signal). As part of your answer, give the command for sending the signal.</li>

Soma: /* Answers */

2012-10-25T18:47:51Z

Answers

← Older revision		Revision as of 18:47, 25 October 2012
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	<li>		<li>
	<li>		<li>
	<li>		<li>NI is the static priority of the process - its "niceness" value. This value can be increased (= priority lowered) by an unprivileged user for their processes using the renice command or the nice system call. (The nice command is used to start a process with a given priority.) The root user can decrease the niceness value as well (increasing the process's priority). The PR column is the process's dynamic priority, a value used by the scheduler to determine which process should run next. The PR value is a function a process's static priority (the NI value) and its recent execution history (is it waiting for I/O, has it used a lot of CPU time, etc).
	</ol>		</ol>

Soma: /* Answers */

2012-10-25T18:31:03Z

Answers

← Older revision		Revision as of 18:31, 25 October 2012
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	</li>		</li>
	<li>Operating systems open files to 1) establish a mapping between a pathname and the contents of the file so that the pathname doesn't have to be parsed on every file access, and 2) so the OS can allocate resources (particularly buffers) to accelerate access to the file. Those buffers can be released (and data flushed to disk) when the file is closed.		<li>Operating systems open files to 1) establish a mapping between a pathname and the contents of the file so that the pathname doesn't have to be parsed on every file access, and 2) so the OS can allocate resources (particularly buffers) to accelerate access to the file. Those buffers can be released (and data flushed to disk) when the file is closed.
	<li>		<li>Library calls are function calls, just to functions stored in dynamic libraries that are "included" with the system. (Note that what is included or not is an ambiguous concept in most Linux distributions.) System calls are invocations of the kernel (typically via a software interrupt). A system call's functionality is typically implemented by C functions; because the kernel must run in supervisor mode and regular programs run in user mode, regular function calls don't work between them. Indeed, userspace programs cannot even directly access the memory of the kernel for security reasons; that is why system calls must be vectored via software interrupts.
	<li>		<li>
	<li>		<li>