Move comment on the 'stepping over resolver' mechanism to the internals manual.

This whole comment is now a bit out of place.  I looked into moving it
to handle_inferior_event, close to where in_solib_dynsym_resolve_code
is used, but then there are 3 such places.  I then looked at
fragmenting it, pushing bits closer to the definitions of
in_solib_dynsym_resolve_code and gdbarch_skip_solib_resolver, but then
we'd lose the main advantage which is the overview.  In the end, I
realized this can fit nicely as internals manual material.

This could possibly be a subsection of a new "run control", or "source
stepping" or "stepping" or some such a bit more general section, but
we can do that when we have more related content...  Even the "single
stepping" section is presently empty...

gdb/doc/
2013-06-27  Pedro Alves  <palves@redhat.com>

	* gdbint.texinfo (Algorithms) <Stepping over runtime loader
	dynamic symbol resolution code>: New section, based on infrun.c
	comment.

gdb/
2013-06-27  Pedro Alves  <palves@redhat.com>

	* infrun.c: Remove comment describing the 'stepping over runtime
	loader dynamic symbol resolution code' mechanism; moved to
	gdbint.texinfo.

2 files changed, 51 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 27d37bd6ed9..afd66e63832 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,9 @@
+2013-06-27  Pedro Alves  <palves@redhat.com>
+
+	* gdbint.texinfo (Algorithms) <Stepping over runtime loader
+	dynamic symbol resolution code>: New section, based on infrun.c
+	comment.
+
 2013-06-26  Tom Tromey  <tromey@redhat.com>
 
 	* gdbint.texinfo (Versions and Branches): Use common/version.in.
diff --git a/gdb/doc/gdbint.texinfo b/gdb/doc/gdbint.texinfo
index 8f826117f5e..749e121332b 100644
--- a/gdb/doc/gdbint.texinfo
+++ b/gdb/doc/gdbint.texinfo
@@ -592,6 +592,51 @@ but @code{placed_size} may be.
 
 @section Single Stepping
 
+@section Stepping over runtime loader dynamic symbol resolution code
+@cindex Procedure Linkage Table, stepping over
+@cindex PLT, stepping over
+@cindex resolver, stepping over
+
+If the program uses ELF-style shared libraries, then calls to
+functions in shared libraries go through stubs, which live in a table
+called the PLT (@dfn{Procedure Linkage Table}).  The first time the
+function is called, the stub sends control to the dynamic linker,
+which looks up the function's real address, patches the stub so that
+future calls will go directly to the function, and then passes control
+to the function.
+
+If we are stepping at the source level, we don't want to see any of
+this --- we just want to skip over the stub and the dynamic linker.
+The simple approach is to single-step until control leaves the dynamic
+linker.
+
+However, on some systems (e.g., Red Hat's 5.2 distribution) the
+dynamic linker calls functions in the shared C library, so you can't
+tell from the PC alone whether the dynamic linker is still running.
+In this case, we use a step-resume breakpoint to get us past the
+dynamic linker, as if we were using @code{next} to step over a
+function call.
+
+The @code{in_solib_dynsym_resolve_code} function says whether we're in
+the dynamic linker code or not.  Normally, this means we single-step.
+However, if @code{gdbarch_skip_solib_resolver} then returns non-zero,
+then its value is an address where we can place a step-resume
+breakpoint to get past the linker's symbol resolution function.
+
+The @code{in_dynsym_resolve_code} hook of the @code{target_so_ops}
+vector can generally be implemented in a pretty portable way, by
+comparing the PC against the address ranges of the dynamic linker's
+sections.
+
+The @code{gdbarch_skip_solib_resolver} implementation is generally
+going to be system-specific, since it depends on internal details of
+the dynamic linker.  It's usually not too hard to figure out where to
+put a breakpoint, but it certainly isn't portable.
+@code{gdbarch_skip_solib_resolver} should do plenty of sanity
+checking.  If it can't figure things out, returning zero and getting
+the (possibly confusing) stepping behavior is better than signaling an
+error, which will obscure the change in the inferior's state.  */
+
 @section Signal Handling
 
 @section Thread Handling