This looks good. I just want to check one thing with you. In point 5 you state that unresolved secondary symbols have a zero value. Are you implying that unresolved secondary symbols should not result in a link or load-time error? If that's the case, you should also make it clear that a secondary reference (STB_SECONDARY/SHN_UNDEF) has lower precedence than a global or weak reference.
Randy > -----Original Message----- > From: generic-...@googlegroups.com [mailto:generic- > a...@googlegroups.com] On Behalf Of H.J. Lu > Sent: Saturday, May 12, 2012 9:53 AM > To: Generic System V Application Binary Interface; GCC Development; > Binutils; GNU C Library; Ansari, Zia > Subject: Add STB_SECONDARY to gABI > > Here is the final proposal to add STB_SECONDARY to gABI. > Any comments? > > Thanks. > > -- > H.J. > --- > We want to provide a relocatable object which can take advantage of all > versions of a supported OS. For a function, foo, in the C library, we > can use it only if it is available on all versions of the C library or > we provide our own implementation of foo. With our own foo, the one in > the C library will never be used. Here is a proposal to add > STB_SECONDARY > to gABI to support the secondary definition so that a software vendor > can provide an alternative implementation in case it isn't available > in the C library. > > STB_SECONDARY > > Secondary symbols are similar to weak symbols, but their definitions > have even lower precedence. The difference between secondary symbols > and weak symbols are > > 1. The link editor must search archive library and extract > archive members to resolve defined and undefined secondary symbol. > 2. When the link editor searches a shared object, it must honor > the global or weak definition in the shared object and ignore the > secondary one with the same name. > 3. The link editor ignores the secondary definition if there is > a global, weak or common definition with the same name. Multiple > secondary definitions with the same name will not cause an error. > The first appearance of the secondary definition should be honored > and the rest are ignored. > 4. The link editor may treat the secondary definition in the > shared object as a global definition. > 5. Unresolved secondary symbols have a zero value. > > The purpose of this symbol binding is to provide the primary > definition as a global, weak or common symbol in an archive library > or a shared object while keeping a secondary definition in a > relocatable object. If there is no primary definition, the > secondary definition will be used. > > When secondary definitions become part of an executable or shared > object, linker may convert them to global or local definitions. > > At run-time, when resolving a symbol, after seeing a secondary > definition, the dynamic linker must keep searching until a > global or weak definition is found. If a global or weak > definition is found, it will be used to satisfy the symbol lookup. > Otherwise, the secondary definition will be used. > > If the dlopen loads a global or weak definition after the program > has already resolved references to a secondary definition, those > references remain bound to the secondary definition. Any > references resolved after the dlopen, for which the dlopened > module is included in the module search list, would be resolved > to the global or weak definition. > > STB_SECONDARY is defined as: > > #define STB_SECONDARY 3 /* Secondary symbol */ > > -- > You received this message because you are subscribed to the Google > Groups "Generic System V Application Binary Interface" group. > To post to this group, send email to generic-...@googlegroups.com. > To unsubscribe from this group, send email to generic- > abi+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/generic-abi?hl=en.