[Valgrind-users] memcheck question

[Mark R. <ma...@cs...>]

The C/C++ front end to our tool Daikon includes most of Valgrind's memcheck
code.  We monitor the execution of a user's program and record the values
seen for various program variables.  As we follow pointer variables, we need
to make sure they point to valid memory before we attempt to read the
contents.  We have seen very intermittent failures in the code, but I think
I have finally got a repeatable one.  Now to my question.

 

We are using "is_mem_defined" (in mc_main.) to test for "is it safe to read
this location?" and that does not appear to be quite right.  It looks as
though an address in a code segment is defined, but not readable.  We get a
SIGSEGV with a bad permissions message when we try.  Whether or not that is
the correct analysis is not as important as the primary question:

 

What is the proper way to check to see if an address is readable?  And,
similarly, is writable?

 

Thank you,

Mark Roberts