Recent Posts by Rod Evans

The runtime linker, ld.so.1(1), is capable of loading relocatable objects. This capability arrived somewhat by accident, and as a side effect of some other projects related to the link-editor, ld(1). But, it was thought that this capability could prove useful within a development environment. A user can preload relocatable objects, and this technique might provide a quick prototyping turnaround instead of having to first combine the relocatable objects into some huge shared...

In a previous posting, I covered how the interface of a dynamic object could be established by defining the interface symbols within a mapfile, and feeding this file to the link-edit of the final object. Establishing an objects interface in this manner hides all non-interface symbols, making the object more robust and less vulnerable to symbol name space pollution. This symbol reduction also goes a long way to reducing the runtime relocation cost of the dynamic object. This map...

With Solaris 10 you can no longer build a static executable. It's not that ld(1) doesn't allow static linking, or using archives, it's just that libc.a, the archive version of libc.so.1, is no longer provided. This library provides the interfaces between user land and the kernel, and without this library it is rather hard to create any form of application. We've been warning users against static linking for some time now, and linking against libc.a has been...

Filters are a class of shared objects that are available with Solaris. These objects allow for the redirection of symbol bindings at runtime. They have been employed to provide standards interfaces and to allow the selection of optimized function implementations at runtime. For those of you unfamiliar with filters, here's an introduction, plus a glimpse of some new techniques available with Solaris 10. Filters can exist in two forms, standard filters and auxiliary filters. At...

Since Solaris 2.0, the link-editors have provided a mechanism for tracing what they're doing. As this mechanism has been around for so long, plus I've used some small examples in previous postings, I figured most folks knew of its existence. I was reminded the other day that this isn't the case. For those of you unfamiliar with this tracing, here's an introduction, plus a glimpse of a new analysis tool available with Solaris 10. You can set the environment variable LD_DEBUG to...

I received an application from a customer the other day. It's quite a big sucker, consisting of the application and over 70 shared objects (that's besides the system objects that also get used). % size -x main \*.so main: 2df35c + 2675a4 + 80918f8 = 0x85d81f8 libxxx.so: 64d4d9c + 9af9f6 + 19604ba = 0x87e4c4c libyyy.so: 4db7aeb + 76aa4c + 32cc16c = 0x87ee6a3 libzzz.so: 3f347ce + d8ebb1 + 4642a3b = 0x9305dba .... The customer has complained that it...

For some time now, we've been versioning core system libraries. You can display version definitions, and version requirements with pvs(1). For example, the latest version of libelf.so.1 from Solaris 10, provides the following versions: % pvs -d /lib/libelf.so.1 libelf.so.1; SUNW_1.5; SUNW_1.4; .... SUNWprivate_1.1; So, what do these versions provide? Shared object versioning has often been established with various conventions of...

In a previous posting I described the use of lazy loading. Of course, when we initially played with an implementation of this technology, a couple of applications immediately fell over. It turns out that a fall back was necessary. Let's say an application developer creates an application with two dependencies. The developer wishes to employ lazy loading for both dependencies. % ldd main foo.so => ./foo.so bar.so => ./bar.so ... The...

In a previous posting I stated that you should only record those dependencies you need, and nothing else. There's another step you can take to reduce start-up processing overhead. Dynamic objects need to resolve symbolic references from each other. Function calls are typically implemented through an indirection that allows the function binding to be deferred until the function call is first made. Because of this deferral, it is also possible to cause the defining dependency to...