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* ld.texinfo: Document PowerPC and PowerPC64 options.

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* gen-doc.texi: Enable.
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Alan Modra 2006-05-05 00:51:37 +00:00
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5
ld/ChangeLog
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@ -1,3 +1,8 @@
2006-05-05 Alan Modra <amodra@bigpond.net.au>
* ld.texinfo: Document PowerPC and PowerPC64 options.
* gen-doc.texi: Enable.
2006-05-02 Daniel Jacobowitz <dan@codesourcery.com>
* Makefile.am (AM_MAKEINFOFLAGS): Add libiberty.

2
ld/gen-doc.texi
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@ -9,6 +9,8 @@
@set HPPA
@set MMIX
@set MSP430
@set POWERPC
@set POWERPC64
@set TICOFF
@set WIN32
@set XTENSA

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ld/ld.texinfo
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@ -40,6 +40,8 @@
@set MSP430
@set PDP11
@set PJ
@set POWERPC
@set POWERPC64
@set SH
@set SPARC
@set TIC54X
@ -156,6 +158,12 @@ section entitled ``GNU Free Documentation License''.
@ifset M68HC11
* M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
@end ifset
@ifset POWERPC
* PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
@end ifset
@ifset POWERPC64
* PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support
@end ifset
@ifset TICOFF
* TI COFF:: ld and the TI COFF
@end ifset
@ -1383,6 +1391,9 @@ This option is only supported on a few targets.
@ifset M68HC11
@xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}.
@end ifset
@ifset POWERPC
@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
@end ifset
On some platforms, the @samp{--relax} option performs global
optimizations that become possible when the linker resolves addressing
@ -5111,6 +5122,12 @@ functionality are not listed.
@ifset M68HC11
* M68HC11/68HC12:: @code{ld} and the Motorola 68HC11 and 68HC12 families
@end ifset
@ifset POWERPC
* PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support
@end ifset
@ifset POWERPC64
* PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support
@end ifset
@ifset TICOFF
* TI COFF:: @command{ld} and TI COFF
@end ifset
@ -5502,6 +5519,183 @@ The last two sections are used by gcc.
@end ifclear
@end ifset
@ifset POWERPC
@ifclear GENERIC
@raisesections
@end ifclear
@node PowerPC ELF32
@section @command{ld} and PowerPC 32-bit ELF Support
@cindex PowerPC long branches
@kindex --relax on PowerPC
Branches on PowerPC processors are limited to a signed 26-bit
displacement, which may result in @command{ld} giving
@samp{relocation truncated to fit} errors with very large programs.
@samp{--relax} enables the generation of trampolines that can access
the entire 32-bit address space. These trampolines are inserted at
section boundaries, so may not themselves be reachable if an input
section exceeds 33M in size.
@cindex PowerPC ELF32 options
@table @option
@cindex PowerPC PLT
@kindex --bss-plt
@item --bss-plt
Current PowerPC GCC accepts a @samp{-msecure-plt} option that
generates code capable of using a newer PLT and GOT layout that has
the security advantage of no executable section ever needing to be
writable and no writable section ever being executable. PowerPC
@command{ld} will generate this layout, including stubs to access the
PLT, if all input files (including startup and static libraries) were
compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old
BSS PLT (and GOT layout) which can give slightly better performance.
@cindex PowerPC GOT
@kindex --sdata-got
@item --sdata-got
The new secure PLT and GOT are placed differently relative to other
sections compared to older BSS PLT and GOT placement. The location of
@code{.plt} must change because the new secure PLT is an initialized
section while the old PLT is uninitialized. The reason for the
@code{.got} change is more subtle: The new placement allows
@code{.got} to be read-only in applications linked with
@samp{-z relro -z now}. However, this placement means that
@code{.sdata} cannot always be used in shared libraries, because the
PowerPC ABI accesses @code{.sdata} in shared libraries from the GOT
pointer. @samp{--sdata-got} forces the old GOT placement. PowerPC
GCC doesn't use @code{.sdata} in shared libraries, so this option is
really only useful for other compilers that may do so.
@cindex PowerPC stub symbols
@kindex --emit-stub-syms
@item --emit-stub-syms
This option causes @command{ld} to label linker stubs with a local
symbol that encodes the stub type and destination.
@cindex PowerPC TLS optimization
@kindex --no-tls-optimize
@item --no-tls-optimize
PowerPC @command{ld} normally performs some optimization of code
sequences used to access Thread-Local Storage. Use this option to
disable the optimization.
@end table
@ifclear GENERIC
@lowersections
@end ifclear
@end ifset
@ifset POWERPC64
@ifclear GENERIC
@raisesections
@end ifclear
@node PowerPC64 ELF64
@section @command{ld} and PowerPC64 64-bit ELF Support
@cindex PowerPC64 ELF64 options
@table @option
@cindex PowerPC64 stub grouping
@kindex --stub-group-size
@item --stub-group-size
Long branch stubs, PLT call stubs and TOC adjusting stubs are placed
by @command{ld} in stub sections located between groups of input sections.
@samp{--stub-group-size} specifies the maximum size of a group of input
sections handled by one stub section. Since branch offsets are signed,
a stub section may serve two groups of input sections, one group before
the stub section, and one group after it. However, when using
conditional branches that require stubs, it may be better (for branch
prediction) that stub sections only serve one group of input sections.
A negative value for @samp{N} chooses this scheme, ensuring that
branches to stubs always use a negative offset. Two special values of
@samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
@command{ld} to automatically size input section groups for the branch types
detected, with the same behaviour regarding stub placement as other
positive or negative values of @samp{N} respectively.
Note that @samp{--stub-group-size} does not split input sections. A
single input section larger than the group size specified will of course
create a larger group (of one section). If input sections are too
large, it may not be possible for a branch to reach its stub.
@cindex PowerPC64 stub symbols
@kindex --emit-stub-syms
@item --emit-stub-syms
This option causes @command{ld} to label linker stubs with a local
symbol that encodes the stub type and destination.
@cindex PowerPC64 dot symbols
@kindex --dotsyms
@kindex --no-dotsyms
@item --dotsyms, --no-dotsyms
These two options control how @command{ld} interprets version patterns
in a version script. Older PowerPC64 compilers emitted both a
function descriptor symbol with the same name as the function, and a
code entry symbol with the name prefixed by a dot (@samp{.}). To
properly version a function @samp{foo}, the version script thus needs
to control both @samp{foo} and @samp{.foo}. The option
@samp{--dotsyms}, on by default, automatically adds the required
dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this
feature.
@cindex PowerPC64 TLS optimization
@kindex --no-tls-optimize
@item --no-tls-optimize
PowerPC64 @command{ld} normally performs some optimization of code
sequences used to access Thread-Local Storage. Use this option to
disable the optimization.
@cindex PowerPC64 OPD optimization
@kindex --no-opd-optimize
@item --no-opd-optimize
PowerPC64 @command{ld} normally removes @code{.opd} section entries
corresponding to deleted link-once functions, or functions removed by
the action of @samp{--gc-sections} or linker scrip @code{/DISCARD/}.
Use this option to disable @code{.opd} optimization.
@cindex PowerPC64 OPD spacing
@kindex --non-overlapping-opd
@item --non-overlapping-opd
Some PowerPC64 compilers have an option to generate compressed
@code{.opd} entries spaced 16 bytes apart, overlapping the third word,
the static chain pointer (unused in C) with the first word of the next
entry. This option expands such entries to the full 24 bytes.
@cindex PowerPC64 TOC optimization
@kindex --no-toc-optimize
@item --no-toc-optimize
PowerPC64 @command{ld} normally removes unused @code{.toc} section
entries. Such entries are detected by examining relocations that
reference the TOC in code sections. A reloc in a deleted code section
marks a TOC word as unneeded, while a reloc in a kept code section
marks a TOC word as needed. Since the TOC may reference itself, TOC
relocs are also examined. TOC words marked as both needed and
unneeded will of course be kept. TOC words without any referencing
reloc are assumed to be part of a multi-word entry, and are kept or
discarded as per the nearest marked preceding word. This works
reliably for compiler generated code, but may be incorrect if assembly
code is used to insert TOC entries. Use this option to disable the
optimization.
@cindex PowerPC64 multi-TOC
@kindex --no-multi-toc
@item --no-multi-toc
By default, PowerPC64 GCC generates code for a TOC model where TOC
entries are accessed with a 16-bit offset from r2. This limits the
total TOC size to 64K. PowerPC64 @command{ld} extends this limit by
grouping code sections such that each group uses less than 64K for its
TOC entries, then inserts r2 adjusting stubs between inter-group
calls. @command{ld} does not split apart input sections, so cannot
help if a single input file has a @code{.toc} section that exceeds
64K, most likely from linking multiple files with @command{ld -r}.
Use this option to turn off this feature.
@end table
@ifclear GENERIC
@lowersections
@end ifclear
@end ifset
@ifset TICOFF
@ifclear GENERIC
@raisesections