In commit c8ff872 ("Support systems without qsort_r"), usage of qsort_r
was eliminated because it is a glibc extension. There was discussion of
creating a utility function that implements qsort_r(), but the approach
described uses thread local variables, so it is not actually reentrant,
and it was dropped to avoid confusion.

However, upcoming commits will also prefer a comparator function which
takes an argument, and they also won't require a reentrant
implementation. Add this helper in with a name that shouldn't spark
confusion: qsort_arg().

Signed-off-by: Stephen Brennan <[email protected]>

This will be reused in an upcoming commit.

Signed-off-by: Stephen Brennan <[email protected]>

The Symbol Finder API gives us the ability to register a dynamic
callback for symbol lookup. However, many common use cases are satisfied
by a simple static list of symbols. Correct and efficient lookup in this
simple case is rather tricky. Implement a new type, SymbolIndex, which
can take a list of symbols and index them for efficient lookup by name
or address.

Signed-off-by: Stephen Brennan <[email protected]>

When properly configured, Linux contains its own symbol table within
kernel memory at runtime. It is exposed as the /proc/kallsyms file,
which is the easiest way to consume it, for live kernels.

However, with recent changes to the Linux kernel in 6.0, necessary
symbols are exposed within VMCOREINFO that allow us to interpret the
data structures inside kernel memory, without needing debuginfo. This
allows us to write helpers that can load kallsyms on vmcores, or on live
systems.

Signed-off-by: Stephen Brennan <[email protected]>

Add Python helpers which load module kallsyms and return a symbol index
for them. Unlike the /proc/kallsyms and built-in kallsyms, these are
quite easy to handle using regular Python & drgn code, so implement them
as Python helpers.

There are (at least) two use cases for these helpers:
1. After loading CTF and built-in vmlinux kallsyms, support for module
   kallsyms is still necessary.
2. Sometimes, people only extract vmlinux DWARF debuginfo. Adding module
   symbols can allow stack traces and other symbolization to work even
   without module debuginfo.

Signed-off-by: Stephen Brennan <[email protected]>

The SymbolIndex structure owns the memory for symbols and names, and
once added to the Program, it cannot be removed. Making copies of any of
these symbols is purely a waste: we should be able to treat them as
static. So add a lifetime and allow the SymbolIndex to specify static,
avoiding unnecessary copies and frees.

Signed-off-by: Stephen Brennan <[email protected]>