FIXADE(3) FIXADE(3)
fixade - misaligned data bus error handler and report generator
subroutine handle_unaligned_traps
subroutine list_by_addr
subroutine summary_listing
subroutine print_unaligned_summary
Fixade is a bus error handler which fields, corrects, and reports bus
errors arising due to misaligned data in Irix programs. The MIPS
architecture, for performance reasons, is very restrictive on the
alignment of data which can be used with its standard instruction set.
Usually, the compilers can guarantee this alignment, however, some
situations exist in which this guarantee cannot be made. These
misalignments may be necessary to satisfy Fortran equivalence statements,
due to mismatched formal/actual parameter types, or due to userinstructed
suppression of common block padding (via use of the -align
switches, see f77(1)). Unless the bus error arising due to a load or
store from a misaligned address is caught, it will cause unexpected
program failure.
Routines in the fixade package provide a bus error handler to catch these
errors, correct them, and allow the program to continue execution. They
also provide a reporting facility so that the causes of these errors can
be located and remedied.
None of the routines of fixade have arguments. The routine
handle_unaligned_traps must be called to initialize the handler. If a
misaligned reference is encountered prior to calling this initialization
routine, the reference will produce a core dump. No other routines of the
trap handler may be called prior to calling this initialization routine.
No other routines of the trap handler need to be called unless a report
of misaligned references is desired. A report of misaligned references
consists of two portions: a summary of the types of misaligned
instructions, their counts and relative frequency. (e.g., 'half aligned
load-word occurred fifteen times, and accounted for 2% of all misaligned
references'); and a listing based either on the instruction addresses at
which the faults occurred, or the data addresses producing the faults.
This listing is either an exhaustive listing (default), or a summary
listing. The summary listing will list the address (either instruction
or data, as opted) associated with the fault, and its absolute and
relative frequency, as a percentage. The exhaustive listing will list
all instruction/data address pairs producing a fault. This listing will
be sorted by the address on which the listing is based (i.e., by
instruction address or data address). By default, the listing is
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FIXADE(3) FIXADE(3)
exhaustive. If only a summary of misalignment errors is desired, the
routine summary_listing must be called immediately after the
initialization routine.
Also by default, the listing is based on instruction addresses. If it is
desired to base the listing on data addresses, the routine list_by_addr
must be invoked during initialization.
Prior to program exit, the routine print_unaligned_summary may be called
to print the listing of bus error events, in either summary or exhaustive
format, as described previously. This listing will go to the standard
output. A sample line of this listing in summary format might be
0x0042445c 1536 33% 67%
where 0x0042445c is the address associated with 1536 faults (33% of the
total). The final percentage is cumulative. Whether the address is of
the data causing the fault or the instruction at which it occurred is
indicated in a printed heading.
New options have been added to f77(1) to generate (much slower) code
which tolerates misalignments (see f77(1)). As discussed previously, use
of these options will suppress the padding of common usually done by the
fortran compiler to align elements. They will also generate code which
uses pessimistic code sequences to avoid bus errors due to misalignment.
No bus errors due to misaligned data will occur in modules compiled with
these new options.
Users desiring to find and repair instances of misaligned data may use
either instruction addresses to decide which modules need to be specially
compiled (see f77(1)), or data addresses to find misalignments. In
either case, a symbol table listing produced by nm(1), using the -Bgn
options, will be necessary to map the addresses to routine (or common
block) names.
Similar functionality is available from the Irix kernel by way of the
sysmips(2) call. This, too, handles the unaligned data traps and
emulates the memory reference in software but does not generate any
reports at program termination.
The use of fixade.o is intended for diagnostic purposes only. Program
efficiency may be severely impacted by its use. In addition, programs
using fixade.o may fail to work under future releases of the operating
system or on future processors.
/usr/lib/fixade.o
/usr/lib32/mips3/fixade.o
/usr/lib32/mips4/fixade.o
/usr/lib64/mips3/fixade.o
/usr/lib64/mips4/fixade.o
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FIXADE(3) FIXADE(3)
Larry Weber
Greg Boyd
f77(1), sysmips(2)
When making an exhaustive listing, the trap handler's tables may
overflow. If this occurs, the message
number events not listed due to insufficient table size.
will be printed at the end of the listing.
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