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The try..endtry statement preserves several bytes of data whenever you ente a try..endtry statement. Upon leaving the try..endtry block (or hitting the unprotected clause), the program restores the exception environment. As long as no exception occurs, the try..endtry statement does not affect the values of any registers upon entry to or upon exit from the try..endtry statement. However, this claim is not true if an exception occurs during the execution of the protected statements. Upon entry into an exception clause, the EAX register contains the exception number, but the values of all other general-purpose registers ar undefined. Because the operating system may have raised the exception in response to a hardware error (and, therefore, has played around with the registers), you can't even assume that the general-purpose registers contain whatever values they happened to contain at the point of the exception. The underlying code that HLA generates for exceptions is subject to change in different versions of the compiler, and certainly it changes across operating systems, so it is never a good idea to experimentally determine what values registers contain in an exception handler and depend on those values in your code. Because entry into an exception handler can scramble the register values, you must ensure that you reload important registers if the code following your endtry clause assumes that the registers contain certain values (i.e., values set in the protected section or values set prior to executing the try..endtry statement). Failure to do so will introduce some nasty defects into your program (and these defects may be very intermittent and difficult to detect because exceptions rarely occur and may not always destrov the value

The try..endtry statement preserves several bytes of data whenever you ente a try..endtry statement. Upon leaving the try..endtry block (or hitting the unprotected clause), the program restores the exception environment. As long as no exception occurs, the try..endtry statement does not affect the values of any registers upon entry to or upon exit from the try..endtry statement. However, this claim is not true if an exception occurs during the execution of the protected statements. Upon entry into an exception clause, the EAX register contains the exception number, but the values of all other general-purpose registers ar undefined. Because the operating system may have raised the exception in response to a hardware error (and, therefore, has played around with the registers), you can't even assume that the general-purpose registers contain whatever values they happened to contain at the point of the exception. The underlying code that HLA generates for exceptions is subject to change in different versions of the compiler, and certainly it changes across operating systems, so it is never a good idea to experimentally determine what values registers contain in an exception handler and depend on those values in your code. Because entry into an exception handler can scramble the register values, you must ensure that you reload important registers if the code following your endtry clause assumes that the registers contain certain values (i.e., values set in the protected section or values set prior to executing the try..endtry statement). Failure to do so will introduce some nasty defects into your program (and these defects may be very intermittent and difficult to detect because exceptions rarely occur and may not always destrov the value

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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The try..endtry statement preserves several bytes of data whenever you enter a try..endtry statement. Upon leaving the try..endtry block (or hitting the unprotected clause), the program restores the exception environment. As long as no exception occurs, the try..endtry statement does not affect the 48 Chapter 1 values of any registers upon entry to or upon exit from the try..endtry statement. However, this claim is not true if an exception occurs during the execution of the protected statements. Upon entry into an exception clause, the EAX register contains the exception number, but the values of all other general-purpose registers are undefined. Because the operating system may have raised the exception in response to a hardware error (and, therefore, has played around with the registers), you can't even assume that the general-purpose registers contain whatever values they happened to contain at the point of the exception. The underlying code that HLA generates for exceptions is subject to change in different versions of the compiler, and certainly it changes across operating systems, so it is never a good idea to experimentally determine what values registers contain in an exception handler and depend on those values in your code. Because entry into an exception handler can scramble the register values, you must ensure that you reload important registers if the code following your endtry clause assumes that the registers contain certain values (i.e., values set in the protected section or values set prior to executing the try..endtry statement). Failure to do so will introduce some nasty defects into your program (and these defects may be very intermittent and difficult to detect because exceptions rarely occur and may not always destroy the value
Transcribed Image Text:The try..endtry statement preserves several bytes of data whenever you enter a try..endtry statement. Upon leaving the try..endtry block (or hitting the unprotected clause), the program restores the exception environment. As long as no exception occurs, the try..endtry statement does not affect the 48 Chapter 1 values of any registers upon entry to or upon exit from the try..endtry statement. However, this claim is not true if an exception occurs during the execution of the protected statements. Upon entry into an exception clause, the EAX register contains the exception number, but the values of all other general-purpose registers are undefined. Because the operating system may have raised the exception in response to a hardware error (and, therefore, has played around with the registers), you can't even assume that the general-purpose registers contain whatever values they happened to contain at the point of the exception. The underlying code that HLA generates for exceptions is subject to change in different versions of the compiler, and certainly it changes across operating systems, so it is never a good idea to experimentally determine what values registers contain in an exception handler and depend on those values in your code. Because entry into an exception handler can scramble the register values, you must ensure that you reload important registers if the code following your endtry clause assumes that the registers contain certain values (i.e., values set in the protected section or values set prior to executing the try..endtry statement). Failure to do so will introduce some nasty defects into your program (and these defects may be very intermittent and difficult to detect because exceptions rarely occur and may not always destroy the value
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