[Bug runtime/31074] On aarch64 the systemtap.base/set_kernel.stp triggers "Unable to handle kernel paging request"

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

https://sourceware.org/bugzilla/show_bug.cgi?id=31074

--- Comment #6 from William Cohen <wcohen at redhat dot com> ---
The code in loc2c-runtime.c  _stp_store_deref_string_() looks like it can write
past the end of the buffer.  The for loop has a loop test of "i < len-1".  When
the for loop exits i == len. The statement after the for loop is:

  err = __stp_put_either('\0', (u8 *)addr + i, seg);

This would be effectively addressing addr + len.  The ranges accessing the
buffer should be 0 to len-1.

For aarch64 the buffer for set_kernel.stp get_buffer function and the
tracepoint_table butt up to each other no padding between them.  Some
tracepoints on aarch64 map to the tracepoint_table[0] which is getting
corrupted.  On x86_64 either nothing is getting mapped to tracepoint_table[0]
or there is some space between the end of buffer and the beginning of
tracepoint_table.

On aarch64 sizeof('\0') is returning 4 rather than 1 as expected for a
character. This would explain 4 bytes of tracepoint_table[0] being 0.

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