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 libaries 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


See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface stability | Stable |
+--------------------+-----------------+

SEE ALSO


cc(1), find(1), isalist(1), ld(1), ld.so.1(1), ldd(1), pvs(1),
dlopen(3C), strerror(3C), Intro(5), attributes(7)


January 29, 2007 APPCERT(1)