Tribblix: manual page: appcert.1

APPCERT(1) User Commands APPCERT(1)

NAME

appcert - examine application-level products for unstable use of
Solaris interfaces

SYNOPSIS

appcert [-h] [-n] [-f infile] [-w working_dir] [-B] [-L]
[-S] {obj | dir}...

DESCRIPTION

The appcert utility examines an application's conformance to the
Solaris Application Binary Interface (ABI). The Solaris ABI defines
the runtime library interfaces in Solaris that are safe and stable
for application use. More specifically, appcert identifies any
dependencies on unstable runtime interfaces, as well as certain other
risks that could cause the product to fail to work on a subsequent
release of Solaris.

appcert checks for:

o Private symbol usage in Solaris libraries. These are
private symbols, that is, functions or data, that are not
intended for developer consumption. They are interfaces
that Solaris libraries use to call one another. These
symbols might change their semantic behavior or even
disappear altogether (so-called demoted symbols), so it
is a good practice to make sure your application does not
depend upon any of them.

o Static linking. In particular, this refers to static
linking of archives libc.a, libsocket.a, and libnsl.a,
that is, instead of dynamically linking the corresponding
shared object .so's. Because the semantics of private
symbol calls from one Solaris library to another can
change from one release to another, it is not a good
practice to hardwire library code into your binary
objects.

o Unbound symbols. These are library symbols (that is,
functions or data) that the dynamic linker could not
resolve when appcert was run. This might be an environment
problem (for example, LD_LIBRARY_PATH) or a build problem
(for example, not specifying -llib and/or -z defs with
compiling). They are flagged to point these problems out
and in case a more serious problem is indicated.

An entire product can be readily examined by appcert (that is, if the
product is a collection of many programs and supporting shared
objects) by referring appcert to the directories where the product is
installed.

To perform its task, appcert constructs a profile of interface
dependencies for each object file within the product (whether an
executable object or shared object), to determine all the Solaris
system interfaces that are depended upon. (Notice that appcert uses
the Solaris runtime linker to make this determination.) These
dependency profiles are then compared to a definition of the Solaris
ABI to identify any interfaces that are Private (unsafe and unstable
for application-level use).

appcert generates a simple roll-up report that indicates which of the
product's components, if any, had liabilities and what those
liabilities were. The report aids developers who are examining their
product's release-to-release stability.

Notice that appcert produces complete interface dependency
information, both the Public (safe and stable) Solaris interfaces and
the Private (non-ABI) interfaces. This information can also be
examined for each product component, if you want.

IMPORTANT: appcert must run in the same environment in which the
application being checked runs. See NOTES.

OPTIONS

The following options are supported:

-B
If appcert is run in batch mode, the output report
will contain one line per binary, beginning with
PASS if no problems were detected for the binary,
FAIL if any problems were found, or INC if the
binary could not be completely checked. Do not
interpret these labels too literally. For example,
PASS just means that none of the appcert warnings
were triggered. These strings are flush left and so
can be selected via grep ^FAIL ..., and so forth.

-f infile
Specifies the file infile that contains a list of
files (one per line) to check. This list is
appended to the list determined from the command
line operands (see OPERANDS below).

-h
Prints out the usage information.

-L
appcert examines your product for the presence of
shared objects. If it finds some, it appends the
directories they reside in to LD_LIBRARY_PATH. Use
this flag to prevent appcert from doing this.

-n
When searching directories for binaries to check,
this option does not follow symbolic links. See
find(1).

-S
Appends Solaris library directories (that is,
/usr/openwin/lib:/usr/dt/lib) to LD_LIBRARY_PATH.

-w working_dir
Identifies the directory in which to run the
library components and create temporary files
(default is /tmp).

OPERANDS

The following operands are supported:

{obj | dir} ...
A complete list of objects and/or directories
that contain the objects constituting the product
to be checked. appcert recursively searches
directories looking for object files; non-object
files are ignored.

EXIT STATUS

The following exit values are returned:

0
appcert ran successfully and found no potential binary stability
problems.

1
appcert failed to run successfully.

2
Some of the objects checked have potential binary stability
problems.

3
No binary objects were located that could be checked.

LIMITATIONS

If the object file to be examined depends on libraries, those
dependencies must be recorded in it (by using the compiler's -l
switch).

If the object file to be examined depends on other shared libraries,
those libraries must be accessible via LD_LIBRARY_PATH or RUNPATH
when appcert is run.

To check 64-bit applications, the machine must be running the 64-bit
Solaris kernel. See isalist(1). Also, the checks for static linking
are currently not done on 64-bit applications.

appcert cannot examine:

o Object files that are completely or partially statically
linked.
Completely statically linked objects are reported as
unstable.

o Executable files that do not have execute permission set.
These are skipped. Shared objects without execute
permission are not skipped.

o Object files that are setuid root.
Due to limitations in ldd(1), these are skipped. Copy
and/or change the permissions to check them.

o Non-ELF file executables such as shell scripts.

o Non-C language interfaces to Solaris; for example, C++ and
Java.
The code itself need not be in C as long as the calls to
Solaris libraries are in C.

OUTPUT FILES

appcert records its findings in the following files in the working
directory (/tmp/appcert.????? by default):

Index
A mapping between checked binaries and the subdirectory in
the working directory in which the output specific to that
binary can be found.

Report
A copy of the rollup report that was displayed on stdout
when appcert was run.

Skipped
A list of binaries that appcert was asked to check but had
to skip, along with a brief reason why each was skipped.

In addition, there is per-object information in the subdirectories
under appcert.?????/objects/, in the following files:

check.demoted_symbols
A list of symbols suspected to be demoted
Solaris symbols.

check.dynamic.private
A list of private Solaris symbols to which
the object makes direct bindings.

check.dynamic.public
A list of public Solaris symbols to which
the object makes direct bindings.

check.dynamic.unbound
A list of symbols not bound by the dynamic
linker when ldd -r was run. For convenience,
ldd output lines containing file not found
are also included.

summary.dynamic
A pretty-printed summary of dynamic bindings
for the objects examined, including tables
of Public and Private symbols used from each
Solaris library.

Other files are temporary files used internally by appcert.

OUTPUT MESSAGES

Private Symbol Use

Private symbols are functions or data variables in a Solaris library
that are not intended for developer or external use. These symbols
are interfaces that the Solaris libraries use to call and communicate
with one another. They are marked in pvs(1) output with the symbol
version name SUNWprivate.

Private symbols can change their semantic behavior or even disappear
altogether (demoted or deprecated symbols), so your application
should not depend upon any of them.

Demoted Symbols

Demoted symbols are functions or data variables in a Solaris library
that were once private to that library and have been removed (or
possibly scoped local to the library) in a later Solaris release. If
your application directly calls one of these demoted symbols, it will
fail to run (relocation error) on the release in which the symbol was
removed and releases thereafter.

In some rare cases, a demoted symbol will return in a later release,
but nevertheless there are still some releases on which the
application will not run.

Sun Microsystems Inc. performed most of the library scoping in the
transition from Solaris 2.5.1 to 2.6. This action was done to
increase binary stability. By making these completely internal
interfaces invisible (that is, they cannot be dynamically linked
against), a developer cannot accidentally or intentionally call these
interfaces. For more information, see the Linker and Libraries Guide,
in particular the chapter on versioning. This document may be found
online at http://docs.sun.com.

Unbound Symbols

Unbound symbols are library symbols (that is, functions or data)
referenced by the application that the dynamic linker could not
resolve when appcert was run. Note: appcert does not actually run
your application, so some aspect of the environment that affects
dynamic linking might not be set properly.

Unbound symbols do not necessarily indicate a potential binary
stability problem. They only mean that when appcert was run, the
runtime dynamic linker could not resolve these symbols.

Unbound symbols might be due to LD_LIBRARY_PATH not being correctly
set. Make sure it is set, so that all of your binary objects can
find all of the libraries they depend on (either your product's own
libraries, Solaris libraries, or those of a third party). Then re-run
appcert.

You might find it useful to write a shell script that sets up the
environment correctly and then runs appcert on the binaries you want
to check.

Another common cause for unbound symbols is when a shared object
under test has not recorded its dynamic dependencies, that is, at
build time the -l switch was not supplied to the compiler and ld(1).
So the shared object requires that the executables that link against
it have the correct dependencies recorded.

Notice that such a shared object can either be linked in the standard
way (that is, specified at an executable's build time) or dynamically
opened (for example, an executable calls dlopen(3C) on the shared
object sometimes when running). Either case can give rise to unbound
symbols when appcert is run. The former can usually be resolved by
setting LD_LIBRARY_PATH appropriately before running appcert. The
latter (dlopen) is usually difficult to resolve. Under some
circumstances, you might be able to set LD_PRELOAD appropriately to
preload the needed libraries, but this procedure does not always
work.

How do you know if the environment has been set up correctly so that
there will be no unbound symbols? It must be set up so that running
ldd -r on the binary yields no "file not found" or "symbol not found"
errors. See ld.so.1(1) and ldd(1) for more information on dynamic
linking.

In any event, appcert flags unbound symbols as a warning in case they
might indicate a more serious problem. Unbound symbols can be an
indicator of dependencies on demoted symbols (symbols that have been
removed from a library or scoped local to it). Dependencies on
demoted symbols will lead to serious binary stability problems.

However, setting up the environment properly should remove most
unbound symbols. In general, it is good practice to record library
dependencies at build time whenever possible because it helps make
the binary object better defined and self-contained. Also recommended
is using the -z defs flag when building shared objects, to force the
resolution of all symbols during compilation. See ld(1) for more
information.

No Bindings Found

appcert runs /bin/ldd -r on each binary object to be tested. It sets
the environment variable LD_DEBUG="files,bindings". (See ldd(1) and
ld.so.1(1) for more information). If that command fails for some
reason, appcert will have no dynamic symbol binding information and
will find "no bindings".

appcert can fail if any of the following is true:

o The binary object does not have read permission.

o The binary object is SUID or SGID and the user does not
have sufficient privileges.

o The binary object is an executable without the execute
permission bit set.

o The binary object is completely statically linked.

o The binary object has no library dependency information
recorded.

Other cases exist as well (for example, out of memory). In general,
this flag means that appcert could not completely examine the object
due to permissions or environment. Try to modify the permissions or
environment so that the dynamic bindings can be recorded.

Obsolete Library

An obsolete library is one whose use is deprecated and that might, in
some future release, be removed from Solaris altogether. appcert
flags these because applications depending on them might not run in
future releases of Solaris. All interfaces, including Private ones,
in an obsolete library are frozen and will not change.

Use of sys_errlist/sys_nerr
Direct use of the symbols sys_errlist or sys_nerr presents a risk in
which reference might be made past the end of the sys_errlist array.
These symbols are deprecated in 32-bit versions of Solaris and are
absent altogether in 64-bit versions. Use strerror(3C) instead.

Use of Strong vs. Weak Symbols
The "strong" symbols (for example, _socket) associated with "weak"
symbols (for example, socket ) are reserved as private (their
behavior could change in the future). Your application should only
directly reference the weak symbol (usually the strong symbols begin
with "_").

Note: Under certain build environments, the strong/private symbol
dependency gets recorded into your binary instead of the weak/public
one, even though the source code doesn't appear to reference the
private symbol. Nevertheless, steps should be taken to trace down
why this is occurring and fix the dependency.

NOTES

appcert needs to run in the same environment in which the application
being checked runs. Otherwise it might not be able to resolve
references correctly to interfaces in the Solaris libraries. Take the
following steps:

1. Make sure that LD_LIBRARY_PATH and any other aspects of
the environment are set to whatever settings are used when
the application is run. Also make sure that it contains
the directories containing any non-Solaris shared objects
that are part of the product, so that they can be found
when referenced.

2. Make sure that all the binaries to be checked:

o Are dynamically linked ELF objects

o Have execute permission set on executables (this is
not necessary for shared objects)

o Are not SUID root (otherwise you will have to be root
to check them; make non-SUID copies and check those if
necessary).

You might find it useful to write a shell script that sets up the
environment correctly and then runs appcert.

Some potential problems that can be encountered are:

o appcert reports unbound symbols that appear to be part of
Solaris libraries.

This is probably caused when the application uses
dlopen(3C) to access a shared object that does not have
its Solaris dependencies recorded. appcert cannot resolve
symbol use in such cases, since the dynamic linker is
never invoked on the shared object, and there is no other
dependency information that could be used to resolve the
Solaris symbol bindings. This can also occur with non-
Solaris symbols.

To avoid this problem, make sure that when a shared object
is built, its dependencies on Solaris libraries are
explicitly recorded by using the -llib option on the
compile line (see cc(1) and ld(1)).

o appcert reports that the application uses a Solaris
private symbol that is not referenced in the application's
source code.

This problem is most likely due to static linking of a
Solaris library that references that symbol. Since appcert
uses the dynamic linker to resolve symbols, statically
linked libraries appear to appcert to be part of the
application code (which, in a sense, they are). This can
also sometimes happen as a result of macro substitution in
a Solaris header file.

To avoid this problem, whenever possible do not statically
link Solaris library archives into your application.

o appcert does not recognize a library as part of Solaris.

Some obsolete Solaris libraries are so old that they were
obsoleted before their symbols could be versioned.
Consequently, appcert cannot recognize them as being part
of Solaris.

BUGS

The use of the terms "public" and "private" as equivalent to "stable"
and "unstable" is unfortunately somewhat confusing. In particular,
experimental or evolving interfaces are public in the sense that they
are documented and their use is encouraged. But they are unstable,
because an application built with them might not run on subsequent
releases. Thus, they are classified as private for appcert's purposes
until they are no longer evolving. Conversely, obsolete interfaces
will eventually disappear, and so are unstable, even though they have
been public and stable in the past and are still treated as public by
appcert. Fortunately, these two situations are rare.

ATTRIBUTES