[Bug runtime/24935] Reading userland static data always leads to read faults on Fedora 29 x86_64

["wcohen at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24935

William Cohen <wcohen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |wcohen at redhat dot com
         Resolution|---                         |NOTABUG

--- Comment #1 from William Cohen <wcohen at redhat dot com> ---
One could have the probe fire after the static string has been accessed by
test.c, for example in the process("function").return for a function that
accesses s. However, in this test.c example for this PR nothing is going to
ever going to cause a page fault to pull in that static page that s points at.

Systemtap can only access pages that are already mapped in.  SystemTap can't
trigger a pagefault to map in a page that is not currently mapped in. A similar
situation was observed on a number of the testsuite/systemtap.syscall tests
where a string was stored on a page that was not mapped in on syscall entry and
the syscall would page fault the string in.  The work around in the syscall
tests was to use mlockall(MCL_CURRENT) to ensure that the string in .rodata
section was mapped in.  One example fix of this is git commit
e67e4b19fd73953fbc8a23c91ae22f9d35a7c817:

Author: William Cohen <wcohen@redhat.com>  2023-11-15 17:01:14
Committer: William Cohen <wcohen@redhat.com>  2023-11-15 17:01:14
Parent: 114de05acfdab36295c9c6beee9715e986810d11 (PR29076: Additional syscall
test fixes for .rodata on x86_64)
Child:  130af146398ca5788be92d258eabe1cee662037f (Tweak
testsuite/semok/target_addr.stp to work with linux 5.14 and newer.)
Branches: master, remotes/origin/master, remotes/origin/mcermak-pr30321,
wcohen/nfs
Follows: release-5.0a
Precedes: 

    PR29076: syscall test fixes for .rodata on x86_64 for pwritev.c and sysfs.c

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