path: root/doc/qa.docbook

<part id='qa'>
<title>Quality Assurance</title>
<chapter id='qa-notices'>
 <title>QA Notices</title>
 <para>
  Here we'll go over each QA notice and what you (as a developer) can do to fix
  the issue.  If you're a user, you should of course go 
  <ulink url="https://bugs.gentoo.org/">file a bug</ulink>.  We'll only cover the
  non-obvious notices here.
 </para>
 <para>
  In pretty much all cases, you should try and get these issues resolved
  upstream rather than simply fixing them in our ebuilds.
 </para>

 <sect1 id='qa-scanelf-runpath'>
  <title>Scanelf: Insecure RUNPATHs</title>
  <para>
   <programlisting>
    QA Notice: The following files contain insecure RUNPATHs
   </programlisting>
  </para>
  <para>
   Some of the ELFs that would be installed on the system have insecure dynamic
   RUNPATH tags.  RUNPATH tags are a hardcoded list of filesystem paths that
   will be searched at runtime when the ELF is executed.  If the ELF has a
   world accessible directory hardcoded in it, then a malicious person can
   inject code at runtime by adding their own libraries to the directory.
  </para>
  <para>
   Here are some of the common problems and their solutions.
   <itemizedlist>
    <listitem>
     <para>Libtool - old versions of libtool would use too many -rpath flags</para>
     <para>Solution: Regenerate the autotool code</para>
    </listitem>
    <listitem>
     <para>Perl - some versions of perl would use incorrect -rpath flags</para>
     <para>Solution: Upgrade system perl build modules</para>
    </listitem>
    <listitem>
     <para>Crappy build system - the custom build system uses -rpath incorrectly</para>
     <para>Solution: Review the LDFLAGS in the build system and make them not suck</para>
    </listitem>
    <listitem>
     <para>Crappy ebuild - the ebuild installs ELFs instead of using the package's build system</para>
     <para>Solution: Fix the crappy ebuild to use the package's build system</para>
    </listitem>
   </itemizedlist>
  </para>
 </sect1>

 <sect1 id='qa-scanelf-textrel'>
  <title>Scanelf: Runtime Text Relocations (TEXTRELS)</title>
  <para>
   <programlisting>
    QA Notice: The following files contain runtime text relocations
   </programlisting>
  </para>
  <para>
   Please see the Gentoo Hardened <ulink url="https://wiki.gentoo.org/wiki/Hardened/Textrels_Guide">PIC Fix Guide</ulink>.
  </para>
 </sect1>

 <sect1 id='qa-scanelf-execstack'>
  <title>Scanelf: Executable Stack (EXECSTACK)</title>
  <para>
   <programlisting>
    QA Notice: The following files contain executable stacks
   </programlisting>
  </para>
  <para>
   Please see the Gentoo Hardened <ulink url="https://wiki.gentoo.org/wiki/Hardened/GNU_stack_quickstart">GNU Stack Guide</ulink>.
  </para>
 </sect1>

 <sect1 id='qa-scanelf-soname'>
  <title>Scanelf: Missing Shared Object Name (SONAME)</title>
  <para>
   <programlisting>
    QA Notice: The following shared libraries lack a SONAME
   </programlisting>
  </para>
  <para>
   A shared library that you would link against lacks an ELF SONAME tag.  With
   simpler libraries, this can be acceptable, but with any sort of ABI sane
   setup, you need the SONAME tag.  This tag is how the system linker tells the
   loader what libraries a program needs at runtime.  With a missing SONAME,
   the linker needs to guess and with many cases, this guess will not work for
   long.
  </para>
  <para>
   To fix this issue, make sure the shared library is linked with the proper
   <option>-Wl,-soname,...</option> flag.  You will need to replace the
   <replaceable>...</replaceable> part with the actual ABI name.  For example,
   if the library is named <filename>libfoo.so.1.2.3</filename>, you will
   probably want to specify <option>-Wl,-soname,libfoo.so.1</option>.
  </para>
  <para>
   Note that this warning only applies to shared libraries that you would link
   against.  It certainly does not apply to plugins that you would dynamically
   load.  However, plugins should not exist in the main library directory, but
   rather an application specific subdirectory in the library directory.  In
   other words, it should be <filename>/usr/lib/app/plugin.so</filename> rather
   than <filename>/usr/lib/plugin.so</filename>.
  </para>
 </sect1>

 <sect1 id='qa-scanelf-needed'>
  <title>Scanelf: Missing Needed Entries</title>
  <para>
   <programlisting>
    QA Notice: The following shared libraries lack NEEDED entries
   </programlisting>
  </para>
  <para>
   This warning comes up when a library does not actually seem to need any
   other libraries in order to run.  Rarely is this true as almost every
   library will need at least the system C library.
  </para>
  <para>
   Once you've determined that the library is indeed being generated
   incorrectly, you will need to dig into the build system to make sure that
   it pulls in the libraries it needs.  Often times, this is because the
   build system invokes the system linker (<command>ld</command>) directly
   instead of the system compiler driver (<command>gcc</command>).
  </para>
 </sect1>

 <sect1 id='qa-abs-lib-link'>
  <title>Absolute Symlink In Library Directory</title>
  <para>
   <programlisting>
    QA Notice: Found an absolute symlink in a library directory
   </programlisting>
  </para>
  <para>
   If you want to use symlinks in library directories, please use either a
   relative symlink or a linker script.  This can cause problems when working
   with cross-compiler systems or when accessing systems in a different ROOT
   directory.
  </para>
  <para>
   If you have a library installed into <filename>/lib/</filename> and you want
   to have it accessible in <filename>/usr/lib/</filename>, then you should
   generate a linker script so that the system toolchain can handle it properly.
   Please see the <link linkend="qa-missing-ldscript">linker script section</link>
   for more information.
  </para>
 </sect1>

 <sect1 id='qa-missing-ldscript'>
  <title>Missing Linker Script</title>
  <para>
   <programlisting>
    QA Notice: Missing gen_usr_ldscript
   </programlisting>
  </para>
  <para>
   If you have a shared library in <filename>/lib/</filename> and a static
   library in <filename>/usr/lib/</filename>, but no linker script in
   <filename>/usr/lib/</filename>, then the toolchain will choose the incorrect
   version when linking.  The system linker will find the static library first
   and not bother searching for a dynamic version.  To overcome this, you need
   to use the <command>gen_usr_ldscript</command> function found in the
   toolchain-funcs.eclass.  Refer to the
   man page for information on how to use it.  See this
   <ulink url="https://bugs.gentoo.org/4411">bug report</ulink> for some history
   on this issue.
  </para>
 </sect1>

 <sect1 id='qa-root-cruft'>
  <title>Excessive Files in /</title>
  <para>
   <programlisting>
    QA Notice: Excessive files found in the / partition
   </programlisting>
  </para>
  <para>
   You should not store files that are not critical to boot and recovery in
   the root filesystem.  This means that static libraries and libtool scripts do
   not belong in the <filename>/lib/</filename> directory.  Fix your ebuild so
   it does not install there.
  </para>
 </sect1>

 <sect1 id='qa-tempdir-libtool'>
  <title>Portage Tempdir In Libtool Scripts</title>
  <para>
   <programlisting>
    QA Notice: ... appears to contain PORTAGE_TMPDIR paths
   </programlisting>
  </para>
  <para>
   Older versions of libtool would incorrectly record the build and/or install
   directory in the libtool script (*.la).  This would lead to problems when
   building other things against your package as libtool would be confused by
   the old paths.
  </para>
  <para>
   You may be able to cheat and use the <command>elibtoolize</command> function
   in the libtool.eclass.  However, if
   that does not help, you will probably need to regenerate all of the autotool
   files.
  </para>
 </sect1>

 <sect1 id='qa-build-strict-aliasing'>
  <title>Build Warning: Strict Aliasing</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               fine but exhibit random runtime failures.
    ...: warning: dereferencing type-punned pointer will break strict-aliasing rules
   </programlisting>
  </para>
  <para>
   This warning crops up when code starts casting distinct pointer types and
   then dereferencing them.  Generally, this is a violation of aliasing rules
   which are part of the C standard.  Historically, these warnings did not show
   up as the optimization was not turned on by default.  With gcc-4.1.x and
   newer though, the -O2 optimization level enables strict aliasing support.
   For information, please review these links:
   <ulink url="https://mail-index.netbsd.org/tech-kern/2003/08/11/0001.html">NetBSD Explanation</ulink>,
   <ulink url="http://thread.gmane.org/gmane.linux.gentoo.devel/39495">Gentoo Dev Thread</ulink>,
   <ulink url="https://gcc.gnu.org/bugs.html#nonbugs_c">GCC Docs</ulink>,
   <ulink url="http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html">Practical examples</ulink>.
  </para>
  <para>
   To fix this issue, use the methods proposed in the links mentioned earlier.
   If you're unable to do so, then a work around would be to append the gcc
   -fno-strict-aliasing flag to CFLAGS in the ebuild.
  </para>
 </sect1>

 <sect1 id='qa-build-implicit-decl'>
  <title>Build Warning: Implicit Declarations</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               fine but exhibit random runtime failures.
    ...: warning: implicit declaration of function ...
    ...: warning: incompatible implicit declaration of built-in function ...
   </programlisting>
  </para>
  <para>
   Your code is calling functions which lack prototypes.  In C++, this would
   have been a build failure, but C is lazy so you just get a warning.  This
   can be a problem as gcc has to guess at what sort of arguments a function
   takes based upon how it was called and often times, this is not the same
   as what the function actually takes.  The function return type is also
   unknown so it's just assumed to be an integer (which is often times wrong).
   This can get to be a problem when the size of the types guessed do not
   actually match the size of the types the function expects.  Generally, this
   corresponds directly to proper coding practices (and the lack thereof).
   Also, by including proper prototypes, the compiler often helps by checking
   types used, proper number of arguments passed, etc...
  </para>
  <para>
   To fix this, just include the proper header files for the functions in
   question.  If the function is a package-specific one, then you may have to
   create a header/function prototype for it.
  </para>
 </sect1>

 <sect1 id='qa-build-uninitialized'>
  <title>Build Warning: Used Uninitialized</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               fine but exhibit random runtime failures.
    ...: warning: is used uninitialized in this function
   </programlisting>
  </para>
  <para>
   This means code uses a variable without actually setting it first.  In other
   words, the code is basically using random garbage.
  </para>
  <para>
   The fix here is simple: make sure variables are initialized properly before
   using them.
  </para>
 </sect1>

 <sect1 id='qa-build-math-compare'>
  <title>Build Warning: Invalid X&lt;=Y&lt;=Z Comparisons</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               fine but exhibit random runtime failures.
    ...: warning: comparisons like X&lt;=Y&lt;=Z do not have their mathematical meaning
   </programlisting>
  </para>
  <para>
   This warning crops up either when the programmer expected the expression
   to work or they just forgot to use sufficient parentheses.  For example,
   the following code snippets are wrong (we won't get into the technical
   argument of this being valid C code; just change the code to not be
   ambiguous).
   <programlisting>
    if (x &lt;= y &lt;= z)
      ...;
    if (a &lt; b &lt;= c)
      ...;
   </programlisting>
  </para>
  <para>
   To fix this, read the code to figure out what exactly the programmer meant.
  </para>
 </sect1>

 <sect1 id='qa-build-non-null'>
  <title>Build Warning: Non-Null Required</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               fine but exhibit random runtime failures.
    ...: warning: null argument where non-null required
   </programlisting>
  </para>
  <para>
   Many functions take pointers as arguments and require that the pointer never
   be NULL.  To this end, you can declare function prototypes that instruct the
   compiler to do simple checks to make sure people do not incorrectly call the
   function with NULL values.  This warning pops up when someone calls a
   function and they use NULL when they should not.  Depending on the library,
   the function may actually crash (they told you not to use NULL after-all, so
   it's your fault :P).
  </para>
  <para>
   You will need to read the code and fix it so that it does not incorrectly
   call the relevant functions with NULL values.
  </para>
 </sect1>

 <sect1 id='qa-build-pointer-trunc'>
  <title>Build Warning: Truncating Pointers</title>
  <para>
   <programlisting>
    QA Notice: Package has poor programming practices which may compile
               but will almost certainly crash on 64bit architectures.
   </programlisting>
  </para>
  <para>
   A large portion of code in the open source world is developed on the 32bit
   x86 architecture.  Unfortunately, this has led to many pieces of code not
   handling pointer types properly.  When compiled and run on a 64bit
   architecture, the code in question will probably crash horribly.  Some
   common examples are assuming that an integer type is large enough to hold
   pointers.  This is true on 32bit architectures (an integer can hold 32bits
   and a pointer is 32bits big), but not true on 64bit architectures (an
   integer still holds just 32bits, but a pointer is 64bits big).
  </para>
  <para>
   Since this issue can manifest itself in many ways (as there are many ways to
   improperly truncate a pointer), you will need to read the source code
   starting with the displayed warning.  Make sure types are declared, used,
   and passed properly.  Make sure that all function prototypes are found (see
   the <link linkend="qa-build-implicit-decl">Implicit Declarations</link>
   section for more information).  So on and so forth.
  </para>
 </sect1>
</chapter>
</part>