User Commands appcert(1)
NAME
appcert - examine application-level products for unstable
use of Solaris interfaces
SYNOPSIS
appcert [-h] [-n] [-f infile] [-w workingdir] [-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 prac-
tice 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,
LDLIBRARYPATH) or a build problem (for example,
not specifying -llib and/or -z defs with compil-
ing). They are flagged to point these problems out
and in case a more serious problem is indicated.
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An entire product can be readily examined by appcert (that
is, if the product is a collection of many programs and sup-
porting shared objects) by referring appcert to the direc-
tories where the product is installed.
To perform its task, appcert constructs a profile of inter-
face dependencies for each object file within the product
(whether an executable object or shared object), to deter-
mine 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 stabil-
ity.
Notice that appcert produces complete interface dependency
information, both the Public (safe and stable) Solaris
interfaces and the Private (non-ABI) interfaces. This infor-
mation 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 out-
put report will contain one line per
binary, beginning with PAS 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, PAS 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.
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This list is appended to the list deter-
mined 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 LDLIBRARYPATH. Use this
flag to prevent appcert from doing this.
-n When searching directories for binaries to
check, this option does not follow sym-
bolic links. See find(1).
-S Appends Solaris library directories (that
is, /usr/openwin/lib:/usr/dt/lib) to
LDLIBRARYPATH.
-w workingdir Identifies the directory in which to run
the library components and create tem-
porary files (default is /tmp).
OPERANDS
The following operands are supported:
{obj dir} ... A complete list of objects and/or direc-
tories that contain the objects consti-
tuting 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.
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2 Some of the objects checked have potential binary sta-
bility 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
LDLIBRARYPATH 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 applica-
tions.
appcert cannot examine:
o Object files that are completely or partially stat-
ically linked.
Completely statically linked objects are reported
as unstable.
o Executable files that do not have execute permis-
sion 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):
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Index A mapping between checked binaries and the sub-
directory 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 sub-
directories under appcert.?????/objects/, in the following
files:
check.demotedsymbols 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 bind-
ings.
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 MESAGES
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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 com-
pletely internal interfaces invisible (that is, they cannot
be dynamically linked against), a developer cannot acciden-
tally or intentionally call these interfaces. For more
information, see the Linker and Libraries Guide, in particu-
lar 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.
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Unbound symbols might be due to LDLIBRARYPATH 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 dependen-
cies 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 run-
ning). Either case can give rise to unbound symbols when
appcert is run. The former can usually be resolved by set-
ting LDLIBRARYPATH appropriately before running appcert.
The latter (dlopen) is usually difficult to resolve. Under
some circumstances, you might be able to set LDPRELOAD
appropriately to preload the needed libraries, but this pro-
cedure 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 sym-
bols (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
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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 LDEBUG="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 exe-
cute permission bit set.
o The binary object is completely statically linked.
o The binary object has no library dependency infor-
mation 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 alto-
gether. 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 syserrlist/sysnerr
Direct use of the symbols syserrlist or sysnerr presents a
risk in which reference might be made past the end of the
syserrlist array. These symbols are deprecated in 32-bit
versions of Solaris and are absent altogether in 64-bit ver-
sions. 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
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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 LDLIBRARYPATH and any other
aspects of the environment are set to whatever set-
tings are used when the application is run. Also
make sure that it contains the directories contain-
ing any non-Solaris shared objects that are part of
the product, so that they can be found when refer-
enced.
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
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object, and there is no other dependency informa-
tion that could be used to resolve the Solaris sym-
bol 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 hap-
pen 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 pub-
lic 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 situa-
tions are rare.
ATRIBUTES
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See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWapct
Interface stability Stable
SEE ALSO
cc(1), find(1), isalist(1), ld(1), ldd(1), ld.so.1(1),
pvs(1), dlopen(3C), strerror(3C), Intro(4), attributes(5)
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