Recent Posts by Ali Bahrami

Solaris 11.4 comes with a new user level command, /usr/bin/kldd. kldd performs ldd style analysis for kernel modules. The ldd utility is used to analyze the dependencies of a userland dynamic object. Given an object, it tells you what other objects it depends on, as well as revealing related details. This is very basic, and very useful ability. ldd has been part of our product since it debuted, along with support for dynamic linking in SunOS 4.0 in late 1988. It subsequently...

Solaris 11.4 comes with a number of enhancements that allow the elfdump utility to display a wealth of information that was previously hidden in Solaris core files. Best of all, this comes without a significant increase in core file size. Core files are ELF files, and as such, can be examined by tools like elfdump. Historically, Solaris core files have contained the following information: Program Headers PT_LOAD program headers for the mappings of objects found in the process....

The generic ELF format does not assign names to program headers. We've changed that with Solaris 11.4. This article describes how and why. So much of ELF revolves around naming, particularly for sections and symbols. Today, noting that nearly everything else in an ELF object is explicitly named, and in particular, that sections have names, it seems like an odd oversight that program headers are nameless. However, when ELF was invented, it was always true that each object had...

(Written: December 2015)   In December of 2015, we added public and documented ELF functions for section compression to libelf, in cooperation with the GNU libutils, whose libelf delivers the same routines. This means that the ELF world now has a stable and portable way to compress non-allocable (debug) data in an ELF object —a big deal in ELF circles. For us, this was the cumulation of a 4 year journey. In this article, I'll tell that story, and describe the new ELF...

(Written: December 2015)   There are 3 basic types of ELF object: ET_REL A relocatable object, commonly called a "dot O" files, because of the ".o" file extension that is commonly used for them. Compilers take in source files and produce relocatable objects. Relocatable objects can be subsequently be combined to create executables or shared objects. Relocatable objects cannot be executed without first being processed by another link-edit (ld) step to create an executable or...

(Written: December 2015)   In Solaris 11 Update 4, the ld mapfile language has gained MATCH and MATCH_REF expressions, which provide the ability to match sections and symbols using regular expressions or glob patterns. In the case of regular expressions, you can also use back substitution to generate replacement names, using substrings from the original matched name. Support for the GNU --version-script option is also added. History These abilities were a long time coming....

(Written: December 2015)  Solaris 11 Update 4 introduces a new set of CRT objects for use by compilers, and others creating specialized low level system objects. This area has always been poorly documented and it took far longer to unravel the history and understand how things are supposed to work, than it look to actually write and test. Unlike the CRT objects they replace, this set is publicly documented and committed, and the same set of objects are delivered uniformly...

(Written: December 2015)   One of the nice simplifications in Solaris 11 Update 4 is that it is no longer necessary to pass the -mt option to the compilers, or to set -D_REENTRANT when building threaded code. Nothing will stop you from doing that, but they no longer do anything, and can be removed. This is going to simplify documentation, and eliminate potential bugs when making system calls. If you're building on Solaris 11.3 or older, you do still need to set -D_REENTRANT,...

(Written: December 2015)   libc Refactoring Over The Years libc has always been the core library in Unix, providing the system calls, and basic math and I/O abilities (e.g. printf). In the era before dynamic linking, it was an archive, libc.a. It's safe to say that some part of libc is in every program. When dynamic linking was introduced to Unix with SunOS 4.x, libc was delivered as a shared library. Years later, we eliminated the ability to create static executables in...