RealView Compilation Tools Compiler Reference Guide - ARM ...

Compiler Command-line Options
--no_unaligned_access
Use --no_unaligned_access to disable the generation of unaligned word
and halfword accesses on ARMv6 processors.
To enable modulo four-byte alignment checking on an ARMv6 target
without unaligned accesses, you must:
• Set the A bit, bit 1, of CP15 register 1 in your initialization code.
• Set the U bit, bit 22, of CP15 register 1 in your initialization code.
The initial value of the U bit is determined by the UBITINIT input
to the core.
Note
Unaligned doubleword accesses, for example unaligned accesses to long
long integers, are not supported by ARM processor cores. Doubleword
accesses must be either eight-byte or four-byte aligned.
The compiler does not provide support for modulo eight-byte alignment
checking. That is, the configuration U = 0, A = 1 in CP15 register 1 is not
supported by the compiler, or more generally, by the RVCT toolset.
The RVCT libraries include special versions of certain library functions
designed to exploit unaligned accesses. To prevent these enhanced library
functions being used when unaligned access support is disabled, you
need to specify --no_unaligned_access on both the compiler command
line and the assembler command line when compiling a mixture of C and
C++ source files and asssembly language source files.
Restrictions
Code compiled for processors supporting unaligned accesses to data can run correctly
only if the choice of alignment support in software matches the choice of alignment
support on the processor core.
See also
• --cpu=name on page 2-15
• Command syntax on page 3-2 in the Assembler Guide
• Alignment support on page 4-43 in the Compiler User Guide.
2.1.118 --use_pch=filename
This option instructs the compiler to use a PCH file with the specified filename as part
of the current compilation.
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