How about stating that the behavior of STB_SECONDARY symbols in areas not specified by this proposal matches that of STB_WEAK?
For example, we may not want to go into runtime details when an unresolved-hence-zero-valued secondary reference (type STT_FUNC) is hit at runtime. In such instances let us ride on the existing definitions of STB_WEAK. In that way, we don’t have to define everything explicitly. Does that look good? -- Supra > -----Original Message----- > From: generic-...@googlegroups.com [mailto:generic- > a...@googlegroups.com] On Behalf Of Lowell, Randy > Sent: 14 May 2012 07:12 PM > To: generic-...@googlegroups.com; GCC Development; Binutils; GNU C > Library; Ansari, Zia > Subject: RE: Add STB_SECONDARY to gABI > > 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. > > -- > 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.
