libcommon: DOF parsing

This commit adds a DOF parser, derived from DTrace v1 but simplified.
The parser is intended to run in a strict-mode seccomp jail, and does no
I/O except via pre-provided file descriptors.  The host side should do
I/O using the functions in dof_parser_host.h.

The seccomp parser child returns output as a stream of dof_parsed_t
records, which are variable-length records with an early size member
(the reader code in dof_parser_host.c takes care of reading the right
amount of data).  Errors are returned as PIT_ERR records in this stream,
or signified by a simple crash (in which case the invoker can simply
restart it).

The parser has a notably noisy debugging mechanism which can be turned
on via make dof_dbg=yes (it is separate from make debugging=yes because
it makes the daemon emit lots of stuff on stderr, which you're unlikely
to want unless you're actually debugging USDT itself).

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

Makeoptions

@@ -1,11 +1,12 @@
 # The implementation of the configurable make options.
 #
 # Oracle Linux DTrace.
-# Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2011, 2022, Oracle and/or its affiliates. All rights reserved.
 # Licensed under the Universal Permissive License v 1.0 as shown at
 # http://oss.oracle.com/licenses/upl.
 
 debugging ?= no
+dof_dbg ?= no
 coverage ?= no
 verbose ?= no
 
@@ -14,12 +15,17 @@ help::
 	@printf "make debugging=yes [targets]   Disable optimization to make debugger use easier\n" >&2
 	@printf "make coverage=yes [targets]    Turn on coverage support in the testsuite\n" >&2
 	@printf "make verbose=yes [target]      Enable verbose building\n" >&2
+	@printf "make dof_dbg=yes [targets]     Turn on especially noisy DOF parser debugging\n" >&2
 	@printf "\n" >&2
 
 ifneq ($(debugging),no)
 override CFLAGS += -O0 -g
 endif
 
+ifneq ($(dof_dbg),no)
+override CFLAGS += -DDOF_DEBUG
+endif
+
 ifneq ($(coverage),no)
 override CFLAGS += -O0 --coverage
 override LDFLAGS += --coverage

libcommon/Build

@@ -9,5 +9,5 @@ LIBS += libcommon
 libcommon_TARGET = libcommon
 libcommon_DIR := $(current-dir)
 libcommon_CPPFLAGS := -Ilibcommon -Ilibproc
-libcommon_SOURCES = uprobes.c dt_list.c
+libcommon_SOURCES = dof_parser.c dof_parser_host.c uprobes.c dt_list.c
 libcommon_LIBSOURCES = libcommon