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* gdbint.texinfo (Target Architecture Definition): Add section 

``Converting an existing Target Architecture to Multi-arch''.
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Andrew Cagney 2002-06-01 20:14:16 +00:00
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gdb/doc/ChangeLog
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@ -1,3 +1,8 @@
2002-06-01 Andrew Cagney <ac131313@redhat.com>
* gdbint.texinfo (Target Architecture Definition): Add section
``Converting an existing Target Architecture to Multi-arch''.
2002-05-30 Andrew Cagney <ac131313@redhat.com>
* gdbint.texinfo (Releasing GDB): Rename ``Obsoleting any code''

162
gdb/doc/gdbint.texinfo
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@ -3885,6 +3885,168 @@ that just @code{#include}s @file{tm-@var{arch}.h} and
@file{config/tm-@var{os}.h}.
@section Converting an existing Target Architecture to Multi-arch
@cindex converting targets to multi-arch
This section describes the current accepted best practice for converting
an existing target architecture to the multi-arch framework.
The process consists of generating, testing, posting and committing a
sequence of patches. Each patch must contain a single change, for
instance:
@itemize @bullet
@item
Directly convert a group of functions into macros (the conversion does
not change the behavior of any of the functions).
@item
Replace a non-multi-arch with a multi-arch mechanism (e.g.,
@code{FRAME_INFO}).
@item
Enable multi-arch level one.
@item
Delete one or more files.
@end itemize
@noindent
There isn't a size limit on a patch, however, a developer is strongly
encouraged to keep the patch size down.
Since each patch is well defined, and since each change has been tested
and shows no regressions, the patches are considered @emph{fairly}
obvious. Such patches, when submitted by developers listed in the
@file{MAINTAINERS} file, do not need approval. Occasional steps in the
process may be more complicated and less clear. The developer is
expected to use their judgment and is encouraged to seek advice as
needed.
@subsection Preparation
The first step is to establish control. Build (with @option{-Werror}
enabled) and test the target so that there is a baseline against which
the debugger can be compared.
At no stage can the test results regress or @value{GDBN} stop compiling
with @option{-Werror}.
@subsection Add the multi-arch initialization code
The objective of this step is to establish the basic multi-arch
framework. It involves
@itemize @bullet
@item
The addition of a @code{@var{arch}_gdbarch_init} function@footnote{The
above is from the original example and uses K&R C. @value{GDBN}
has since converted to ISO C but lets ignore that.} that creates
the architecture:
@smallexample
static struct gdbarch *
d10v_gdbarch_init (info, arches)
struct gdbarch_info info;
struct gdbarch_list *arches;
@{
struct gdbarch *gdbarch;
/* there is only one d10v architecture */
if (arches != NULL)
return arches->gdbarch;
gdbarch = gdbarch_alloc (&info, NULL);
return gdbarch;
@}
@end smallexample
@noindent
@emph{}
@item
A per-architecture dump function to print any architecture specific
information:
@smallexample
static void
mips_dump_tdep (struct gdbarch *current_gdbarch,
struct ui_file *file)
@{
@dots{} code to print architecture specific info @dots{}
@}
@end smallexample
@item
A change to @code{_initialize_@var{arch}_tdep} to register this new
architecture:
@smallexample
void
_initialize_mips_tdep (void)
@{
gdbarch_register (bfd_arch_mips, mips_gdbarch_init,
mips_dump_tdep);
@end smallexample
@item
Add the macro @code{GDB_MULTI_ARCH}, defined as 0 (zero), to the file@*
@file{config/@var{arch}/tm-@var{arch}.h}.
@end itemize
@subsection Update multi-arch incompatible mechanisms
Some mechanisms do not work with multi-arch. They include:
@table @code
@item EXTRA_FRAME_INFO
Delete.
@item FRAME_FIND_SAVED_REGS
Replaced with @code{FRAME_INIT_SAVED_REGS}
@end table
@noindent
At this stage you could also consider converting the macros into
functions.
@subsection Prepare for multi-arch level to one
Temporally set @code{GDB_MULTI_ARCH} to @code{GDB_MULTI_ARCH_PARTIAL}
and then build and start @value{GDBN} (the change should not be
committed). @value{GDBN} may not build, and once built, it may die with
an internal error listing the architecture methods that must be
provided.
Fix any build problems (patch(es)).
Convert all the architecture methods listed, which are only macros, into
functions (patch(es)).
Update @code{@var{arch}_gdbarch_init} to set all the missing
architecture methods and wrap the corresponding macros in @code{#if
!GDB_MULTI_ARCH} (patch(es)).
@subsection Set multi-arch level one
Change the value of @code{GDB_MULTI_ARCH} to GDB_MULTI_ARCH_PARTIAL (a
single patch).
Any problems with throwing ``the switch'' should have been fixed
already.
@subsection Convert remaining macros
Suggest converting macros into functions (and setting the corresponding
architecture method) in small batches.
@subsection Set multi-arch level to two
This should go smoothly.
@subsection Delete the TM file
The @file{tm-@var{arch}.h} can be deleted. @file{@var{arch}.mt} and
@file{configure.in} updated.
@node Target Vector Definition
@chapter Target Vector Definition