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SYS$$QIO entries in System Service Call trace file

wbecker
Occasional Visitor

SYS$$QIO entries in System Service Call trace file

Tracing System Service Calls with set process/sslog I can see for example SYS$$QIO or other SYY$$* entries in the trace log.

Is there a difference between SYS$$QIO and SYS$QIO?

1 REPLY
John Gillings
Honored Contributor

Re: SYS$$QIO entries in System Service Call trace file

Waving hands... the answer to "Is there a difference between SYS$$QIO and SYS$QIO?" is "not really".

 

The thing you refer to when you make a reference to SYS$QIO isn't a routine entry point. It's effectively an entry in a dispatch table, which is used to find the actual code (described in excruciating detail in the Internals and Data Structures manual, Section 7.5 CHANGE MODE DISPATCHING). There are several symbols associated with each system service, including the one prefixed SYS$$. The "$$" indicates an internal system defined symbol. 

 

Somewhere around the web there's a paper written by Ruth Goldenberg which describes how system service tracing works. Ultimately, some address needs to be symbolised (basically a reverse lookup in a symbol table). Where that happens and which address is used will determine which symbol is chosen. As long as it's clear which system service is involved, I guess it doesn't matter how many $ signs are displayed. 

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