4.7 ld
and PowerPC 32-bit ELF Support
Branches on PowerPC processors are limited to a signed 26-bit
displacement, which may result in ld
giving
`relocation truncated to fit' errors with very large programs.
`--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.
- `--bss-plt'
- Current PowerPC GCC accepts a `-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
ld
will generate this layout, including stubs to access the
PLT, if all input files (including startup and static libraries) were
compiled with `-msecure-plt'. `--bss-plt' forces the old
BSS PLT (and GOT layout) which can give slightly better performance.
- `--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
.plt
must change because the new secure PLT is an initialized
section while the old PLT is uninitialized. The reason for the
.got
change is more subtle: The new placement allows
.got
to be read-only in applications linked with
`-z relro -z now'. However, this placement means that
.sdata
cannot always be used in shared libraries, because the
PowerPC ABI accesses .sdata
in shared libraries from the GOT
pointer. `--sdata-got' forces the old GOT placement. PowerPC
GCC doesn't use .sdata
in shared libraries, so this option is
really only useful for other compilers that may do so.
- `--emit-stub-syms'
- This option causes
ld
to label linker stubs with a local
symbol that encodes the stub type and destination.
- `--no-tls-optimize'
- PowerPC
ld
normally performs some optimization of code
sequences used to access Thread-Local Storage. Use this option to
disable the optimization.
This document was generated
by system on July, 22 2007
using texi2html