2 How to add Binary Annotations to your application.

Normally the option to enable the recording of binary annotation notes is enabled automatically by the build system, so no user intervention is required. On Fedora and RHEL based systems this is handled by the ‘redhat-rpm-config’ package.

Currently the binary annotations are generated by a plugin to the compiler (GCC, clang or llvm). This does mean that files that are not compiled by any of these compilers will not gain any annotations, although there is an optional assembler switch to add some basic notes if none are present in the input files.

If the build system being used does not automatically enable the annobin plugin then it can be specifically added to the compiler command line by adding the -fplugin=annobin (for gcc) or -fplugin=annobin-for-clang (for clang) or -fplugin=annobin-for-llvm (for LLVM) option. It may also be necessary to tell the compiler where to find the plugin by adding the -iplugindir= option, although this should only be necessary if the plugin is installed in an unusual place.

If it is desired to disable the recording of binary annotations then the -fplugin-arg-annobin-disable (for gcc) or -Xclang -plugin-arg-annobin-disable (for clang or llvm) can be used. Note - these options must be placed after the -fplugin=annobin option.

On Fedora and RHEL systems the plugin can be disabled entirely for all compilations in a package by adding %undefine _annotated_build to the spec file.

The plugin accepts a small selection of command line arguments, all accessed by passing -fplugin-arg-annobin-<option> (for gcc) or -Xclang -plugin-arg-annobin-<option> (for clang or llvm) on the command line. These options must be placed on the command line after the plugin itself is mentioned. Note - not all versions of the plugin accept all of these options.

In addition it is possible to pass options via the ANNOBIN environment variable. Multiple arguments must be separated by commas, and arguments that need a value must use an equals sign rather than a space or colon.

Also - in order to support backwards compatibility - the LLVM plugin detects the ANNOBIN_VERBOSE enviroment variable and turns on verbose mode if it is present.

The supported options are:


Either disable or enable the plugin. The default is for the plugin to be enabled.


Display a list of supported options on the standard output. This is in addition to whatever else the plugin has been instructed to do.


Display the version of the plugin on the standard output. This is in addition to whatever else the plugin has been instructed to do.


Report the actions that the plugin is taking. If invoked for a second time on the command line the plugin will be very verbose.


Report the generation of function specific notes. This indicates that the named function was compiled with different options from those that were globally enabled.


Do, or do not, record information about the stack requirements of functions in the executable. This feature is disabled by default as these notes can take up a lot of extra room if the executable contains a lot of functions.


If stack size requirements are being recorded then this option sets the minimum value to record. Functions which require less than N bytes of static stack space will not have their requirements recorded. If not set, then N defaults to 1024.


If enabled the global-file-syms option will create globally visible, unique symbols to mark the start and end of the compiled code. This can be desirable if a program consists of multiple source files with the same name, or if it links to a library that was built with source files of the same name as the program itself. The disadvantage of this feature however is that the unique names are based upon the time of the build, so repeated builds of the same source will have different symbol names inside it. This breaks the functionality of the build-id system which is meant to identify similar builds created at different times. This feature is disabled by default, and if enabled can be disabled again via the no-global-file-syms option.


When gcc compiles code with the -ffunction-sections option active it will place each function into its own section. When the annobin attach option is active the plugin will attempt to attach the function section to a group containing the notes and relocations for the function. In that way, if the linker decides to discard the function, it will also know that it should discard the notes and relocations as well.

The default is attach, but this can be disabled via the no-attach option. Note however that if both attach and link-order are disabled then note generation for function sections will not work properly.


As an alternative to using section groups and a special assembler directive the plugin can use a feature of the ELF SHF_LINK_ORDER flag which tells the linker that it should discard a section if the section it is linked to is also being discarded. This behaviour is enabled by the link-order option.


Adds an extra prefix to the symbol names generated by the annobin plugin. This allows the plugin to be run twice on the same executable, which can be useful for debugging and build testing.


The annobin plugin will normally generate warning messages if it detects that certain preprocessor command line options are missing or misspelt. The active-checks option changes the warnings into errors, just as if -Werror had been specified. The no-active-checks option disables the messages entirely.

Currently the plugin checks for these issues:


This warning is generated when neither -D_FORTIFY_SOURCE=2 nor -D_FORTIFY_SOURCE=3 have been provided on the command line and the -flto option has been enabled.

Nomrally this problem would be detected by the annocheck tool, but LTO compilation hides preprocessor options, so information about them cannot be passed on by the plugin. This is why the plugin will generate a warning message when the _FORTIFY_SOURCE option is missing and LTO is enabled.


The plugin will warn if the -D_FORTIFY_SOURCE option is spelt as either -DFORTIFY_SOURCE or -D__FORTIFY_SOURCE.


The plugin will warn if the -D_GLIBCXX_ASSERTIONS option is spelt as either -DGLIBCXX_ASSERTIONS or -D__GLIBCXX_ASSERTIONS.

Note - in the future the annobin plugin might be extended to produce warning messages for other missing command line options.

Note - as a workaround for certain tests generated by the autoconf tool the warning message will not be produced if the input source filename starts with conftest.. In these cases autoconf is usually checking to see if a warning will be produced for some other reason, and so the annobin warning would get in the way. If the active-checks option has been enabled however, an error message will still be generated.


These options are deprecated.


This option either enables or disables the insertion of NOP instructions in the some of the code sections of PowerPC64 binaries. This is necessary to avoid problems with the elflint program which will complain about binaries built without this option enabled. The option is enabled by default, but since it does increase the size of compiled programs by a small amount, the no-ppc64-nops is provided in order to turn it off.


This option chooses the format used to store the information generated by the plugin. The possibilities are:


Store the information as ELF format notes in the .gnu.build.attributes section.


Store the information as mergeable strings in the .annobin.notes section.

The default is note.

The plugins record information appropriate to the compiler that is running them. So the gcc plugin records information about the following options:

-mbranch-protection (AArch64)
-mstack-realign (i386)
-mtls-size (PowerPC)

The Clang plugin records information on the following command line options:


Note - if LTO compilation is enabled (-flto) then any data recorded by the Clang plugin is ignored when the object file is recompiled by the LLVM backend. Hence when using LTO and Clang it is best to enable the LLVM plugin.

The LLVM plugin records information on the following command line options: