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RE: Add STB_SECONDARY to gABI
- From: "Lowell, Randy" <Randy dot Lowell at hp dot com>
- To: "generic-abi at googlegroups dot com" <generic-abi at googlegroups dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>, Binutils <binutils at sourceware dot org>, "GNU C Library" <libc-alpha at sourceware dot org>, "Ansari, Zia" <zia dot ansari at intel dot com>
- Date: Thu, 28 Jun 2012 13:43:57 +0000
- Subject: RE: Add STB_SECONDARY to gABI
- References: <CAMe9rOp5KkoVJV52nRO_X5ek-hSScttSZFgJgQNAHnYVybCKHQ@mail.gmail.com> <F4135B89B3F3E8418F97AC4644C7678D3AE913E6@G9W0750.americas.hpqcorp.net> <email@example.com> <F4135B89B3F3E8418F97AC4644C7678D3AE914D0@G9W0750.americas.hpqcorp.net> <CAMe9rOpkTfoR1-0nDquDQsm96yp0YzghfDNc_sRm62J47X1Z-Q@mail.gmail.com>
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
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:generic-
> email@example.com] On Behalf Of H.J. Lu
> Sent: Wednesday, June 27, 2012 12:06 PM
> To: firstname.lastname@example.org
> Cc: GCC Development; Binutils; GNU C Library; Ansari, Zia
> Subject: Re: Add STB_SECONDARY to gABI
> Resending with plain text.
> Here is the final proposal to add STB_SECONDARY to gABI.
> Any comments?
> 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.
> 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 */
> The behavior of secondary symbols in areas not specified by this
> proposal is implementation defined.
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