This looks good. I just have one wordsmithing comment. I would have listed the STB_SECONDARY differences in a different order -- maybe (3 1 2 4). That puts the most general difference first, and it matches the order used for the description of STB_WEAK.
Randy > -----Original Message----- > From: generic-...@googlegroups.com [mailto:generic- > a...@googlegroups.com] On Behalf Of H.J. Lu > Sent: Wednesday, June 27, 2012 12:06 PM > To: generic-...@googlegroups.com > Cc: GCC Development; Binutils; GNU C Library; Ansari, Zia > Subject: Re: Add STB_SECONDARY to gABI > > Hi, > > Resending with plain text. > > 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 lower precedence than global and week symbols. 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. > > 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 */ > > NOTE: > The behavior of secondary symbols in areas not specified by this > proposal is implementation defined. > > -- > 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.
