* [x86-64 psABI] Document STT_GNU_IFUNC and R_X86_64_IRELATIVE
@ 2012-04-10 15:33 H.J. Lu
2012-04-16 16:52 ` H.J. Lu
0 siblings, 1 reply; 3+ messages in thread
From: H.J. Lu @ 2012-04-10 15:33 UTC (permalink / raw)
To: discuss, GCC Development, Binutils, GNU C Library, GDB
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Hi,
This patch for x86-64 psABI adds document for STT_GNU_IFUNC and
R_X86_64_IRELATIVE. It has been implemented on Linux/x86-64 for
more than a year. Please add it to x86-64 psABI.
Thanks.
--
H.J.
[-- Attachment #2: ifunc-spec.patch --]
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2010-12-30 H.J. Lu <hongjiu.lu@intel.com>
* object-files.tex: Document STT_GNU_IFUNC and R_X86_64_IRELATIVE.
diff --git a/object-files.tex b/object-files.tex
index 757a25d..4705e96 100644
--- a/object-files.tex
+++ b/object-files.tex
@@ -344,6 +344,23 @@ the section until the end, counting entries as they are encountered.
The discussion of "Function Addresses" in Section \ref{function_addresses}
defines some special values for symbol table fields.
+The \texttt{STT_GNU_IFUNC}
+\footnote{It is specified in {\bf ifunc.txt}
+at \url{http://groups.google.com/group/generic-abi/files}}
+symbol type is optional. It is the same as
+\texttt{STT_FUNC} except that it always points to a function or piece of
+executable code which takes no arguments and returns a function pointer.
+If an \texttt{STT_GNU_IFUNC} symbol is referred to by a relocation, then
+evaluation of that relocation is delayed until load-time. The value
+used in the relocation is the function pointer returned by an invocation
+of the \texttt{STT_GNU_IFUNC} symbol.
+
+The purpose of the \texttt{STT_GNU_IFUNC} symbol type is to allow the
+run-time to select between multiple versions of the implementation of
+a specific function. The selection made in general will take the
+currently available hardware into account and select the most
+appropriate version.
+
\section{Relocation}
\subsection{Relocation Types}
@@ -451,6 +468,7 @@ the relocation addend.
\texttt{R_X86_64_GOTPC32_TLSDESC} & 34 & \textit{word32} & \\
\texttt{R_X86_64_TLSDESC_CALL} & 35 & none & \\
\texttt{R_X86_64_TLSDESC} & 36 & \textit{word64}$\times 2$ & \\
+ \texttt{R_X86_64_IRELATIVE} & 37 & \textit{word64} & \texttt{indirect (B + A)}\\
% \texttt{R_X86_64_GOT64} & 16 & \textit{word64} & \texttt{G + A} \\
% \texttt{R_X86_64_PLT64} & 17 & \textit{word64} & \texttt{L + A - P} \\
\end{tabular}
@@ -563,6 +581,16 @@ to the named symbol. \texttt{R_X86_64_TLSDESC_CALL} must annotate the
instruction used to call the TLS Descriptor resolver function, so as
to enable relaxation of that instruction.
+\texttt{R_X86_64_IRELATIVE} is similar to \texttt{R_X86_64_RELATIVE}
+except that the value used in this relocation is the program address
+returned by the function, which takes no arguments, at the address of
+the result of the corresponding \texttt{R_X86_64_RELATIVE} relocation.
+
+One use of the \texttt{R_X86_64_IRELATIVE} relocation is to avoid name
+lookup for the locally defined \texttt{STT_GNU_IFUNC} symbols at
+load-time. Support for this relocation is optional, but is required for
+the \texttt{STT_GNU_IFUNC} symbols.
+
\subsection{Large Models}
In order to extend both the PLT and the GOT beyond 2GB, it
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [x86-64 psABI] Document STT_GNU_IFUNC and R_X86_64_IRELATIVE
2012-04-10 15:33 [x86-64 psABI] Document STT_GNU_IFUNC and R_X86_64_IRELATIVE H.J. Lu
@ 2012-04-16 16:52 ` H.J. Lu
2012-04-17 12:42 ` Michael Matz
0 siblings, 1 reply; 3+ messages in thread
From: H.J. Lu @ 2012-04-16 16:52 UTC (permalink / raw)
To: discuss, GCC Development, Binutils, GNU C Library, GDB, Michael Matz
On Tue, Apr 10, 2012 at 8:33 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> Hi,
>
> This patch for x86-64 psABI adds document for STT_GNU_IFUNC and
> R_X86_64_IRELATIVE. It has been implemented on Linux/x86-64 for
> more than a year. Please add it to x86-64 psABI.
>
> Thanks.
>
Hi Michael,
Can you apply IFUNC spec to x86-64 psABI?
BTW, where can I find the latest x86-64 psABI source? The svn
site:
https://www.x86-64.org/svn/trunk/x86-64-ABI
is down.
Thanks.
--
H.J.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [x86-64 psABI] Document STT_GNU_IFUNC and R_X86_64_IRELATIVE
2012-04-16 16:52 ` H.J. Lu
@ 2012-04-17 12:42 ` Michael Matz
0 siblings, 0 replies; 3+ messages in thread
From: Michael Matz @ 2012-04-17 12:42 UTC (permalink / raw)
To: H.J. Lu; +Cc: discuss, GCC Development, Binutils, GNU C Library, GDB
Hi,
On Mon, 16 Apr 2012, H.J. Lu wrote:
> Hi Michael,
>
> Can you apply IFUNC spec to x86-64 psABI?
Yes, ...
> BTW, where can I find the latest x86-64 psABI source? The svn
> site:
>
> https://www.x86-64.org/svn/trunk/x86-64-ABI
>
> is down.
... once I find out what the problem with that is :)
Ciao,
Michael.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-04-16 16:52 ` H.J. Lu
2012-04-17 12:42 ` Michael Matz
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