468 lines
17 KiB
Plaintext
468 lines
17 KiB
Plaintext
o Call module as module.
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Until now, everything is called as attribute. Separate module from it:
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- Module is a collection of code (*.[cSo]), and provides a function.
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Module can depend on other modules.
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- Attribute provides metadata for modules. One module can have
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multiple attributes. Attribute doesn't generate a module (*.o,
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*.ko).
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o Emit everything (ioconf.*, Makefile, ...) per-attribute.
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config(9) related metadata (cfdriver, cfattach, cfdata, ...) should be
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collected using linker. Create ELF sections like
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.{rodata,data}.config.{cfdriver,cfattach,cfdata}. Provide reference
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symbols (e.g. cfdriverinit[]) using linker script. Sort entries by name
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to lookup entries by binary search in kernel.
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o Generate modular(9) related information. Especially module dependency.
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At this moment modular(9) modules hardcode dependency in *.c using the
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MODULE() macro:
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MODULE(MODULE_CLASS_DRIVER, hdaudio, "pci");
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This information already exists in config(5) definitions (files.*).
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Extend config(5) to be able to specify module's class.
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Ideally these module metadata are kept somewhere in ELF headers, so that
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loaders (e.g. boot(8)) can easily read. One idea is to abuse DYNAMIC
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sections to record dependency, as shared library does. (Feasibility
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unknown.)
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o Rename "interface attribute" to "bus".
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Instead of
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define audiobus {}
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attach audio at audiobus
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Do like this
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defbus audiobus {}
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attach audio at audiobus
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Always provide xxxbusprint() (and xxxbussubmatch if multiple children).
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Extend struct cfiattrdata like:
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struct cfiattrdata {
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const char *ci_name;
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cfprint_t ci_print;
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cfsubmatch_t ci_submatch;
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int ci_loclen;
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const struct cflocdesc ci_locdesc[];
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};
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o Simplify child configuration API
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With said struct cfiattrdata extension, config_found*() can omit
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print/submatch args. If the found child is known (e.g., "pcibus" creating
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"pci"):
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config_found(self, "pcibus");
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If finding unknown children (e.g. "pci" finding pci devices):
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config_find(self, "pci", locs, aux);
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o Retire "attach foo at bar with foo_bar.c"
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Most of these should be rewritten by defining a common interface attribute
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"foobus", instead of writing multiple attachments. com(4), ld(4), ehci(4)
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are typical examples. For ehci(4), EHCI-capable controller drivers implement
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"ehcibus" interface, like:
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defne ehcibus {}
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device imxehci: ehcibus
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These drivers' attach functions call config_found() to attach ehci(4) via
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the "ehcibus" interface attribute, instead of calling ehci_init() directly.
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Same for com(4) (com_attach_subr()) and ld(4) (ldattach()).
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o Sort objects in more reasonable order.
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Put machdep.ko in the lowest address. uvm.ko and kern.ko follow.
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Kill alphabetical sort (${OBJS:O} in sys/conf/Makefile.inc.kern.
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Use ldscript. Do like this
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.text :
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AT (ADDR(.text) & 0x0fffffff)
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{
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*(.text.machdep.locore.entry)
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*(.text.machdep.locore)
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*(.text.machdep)
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*(.text)
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*(.text.*)
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:
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Kill linker definitions in sys/conf/Makefile.inc.kern.
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o Differentiate "options" and "flags"/"params".
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"options" enables features by adding *.c files (via attributes).
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"flags" and "params" are to change contents of *.c files. These don't add
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*.c files to the result kernel, or don't build attributes (modules).
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o Make flags/params per attributes (modules).
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Basically flags and params are cpp(1) #define's generated in opt_*.h. Make
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them local to one attributes (modules). Flags/params which affects files
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across attributes (modules) are possible, but should be discouraged.
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o Generate things only by definitions.
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In the ideal dynamically modular world, "selection" will be done not at
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compile time but at runtime. Users select their wanted modules, by
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dynamically loading them.
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This means that the system provides all choices; that is, build all modules
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in the source tree. Necessary information is defined in the "definition"
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part.
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o Split cfdata.
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cfdata is a set of pattern matching rules to enable devices at runtime device
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auto-configuration. It is pure data and can (should) be generated separately
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from the code.
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o Allow easier adding and removing of options.
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It should be possible to add or remove options, flags, etc.,
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without regard to whether or not they are already defined.
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For example, a configuration like this:
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include GENERIC
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options FOO
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no options BAR
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should work regardless of whether or not options FOO and/or
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options BAR were defined in GENERIC. It should not give
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errors like "options BAR was already defined" or "options FOO
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was not defined".
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o Introduce "class".
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Every module should be classified as at least one class, as modular(9)
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modules already do. For example, file systems are marked as "vfs", network
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protocols are "netproto".
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Consider to merge "devclass" into "class".
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For syntax clarity, class names could be used as a keyword to select the
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class's instance module:
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# Define net80211 module as netproto class
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class netproto
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define net80211: netproto
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# Select net80211 to be builtin
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netproto net80211
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Accordingly device/attach selection syntax should be revisited.
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o Support kernel constructor/destructor (.kctors/.kdtors)
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Initialization and finalization should be called via constructors and
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destructors. Don't hardcode those sequences as sys/kern/init_main.c:main()
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does.
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The order of .kctors/.kdtors is resolved by dependency. The difference from
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userland is that in kernel depended ones are located in lower addresses;
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"machdep" module is the lowest. Thus the lowest entry in .ctors must be
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executed the first.
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The .kctors/.kdtors entries are executed by kernel's main() function, unlike
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userland where start code executes .ctors/.dtors before main(). The hardcoded
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sequence of various subsystem initializations in init_main.c:main() will be
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replaced by an array of .kctors invocations, and #ifdef's there will be gone.
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o Hide link-set in the final kernel.
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Link-set is used to collect references (pointers) at link time. It relys on
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the ld(1) behavior that it automatically generates `__start_X' and `__stop_X'
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symbols for the section `X' to reduce coding.
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Don't allow kernel subsystems create random ELF sections.
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Pre-define all the available link-set names and pre-generate a linker script
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to merge them into .rodata.
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(For modular(9) modules, `link_set_modules' is looked up by kernel loader.
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Provide only it.)
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Provide a way for 3rd party modules to declare extra link-set.
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o Shared kernel objects.
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Since NetBSD has not established a clear kernel ABI, every single kernel
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has to build all the objects by their own. As a result, similar kernels
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(e.g. evbarm kernels) repeatedly compile similar objects, that is waste of
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energy & space.
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Share them if possible. For evb* ports, ideally everything except machdep.ko
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should be shared.
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While leaving optimizations as options (CPU specific optimizations, inlined
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bus_space(9) operations, etc.) for users, the official binaries build
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provided by TNF should be as portable as possible.
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o Always use explicit kernel linker script.
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ld(1) has an option -T <ldscript> to use a given linker script. If not
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specified, a default, built-in linker script, mainly meant for userland
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programs, is used.
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Currently m68k, sh3, and vax don't have kernel linker scripts. These work
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because these have no constraints about page boundary; they map and access
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kernel .text/.data in the same way.
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o Pass input files to ${LD} via linker script.
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Instead of passing input files on command-line, output "INPUT(xxx.o)"
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commands, and include it from generated linker scripts.
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o Directly generate `*.d' files.
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Output source/object files in raw texts instead of `Makefile'. Generate
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`*.d' (make(1) depend) files. make(1) knows which object files are to be
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compiled. With "INPUT(xxx.o)" linker scripts, either generated `Makefile'
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or `Makefile.kern.inc' don't need to keep source/object files in variables.
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o Control ELF sections using linker script.
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Now kernel is linked and built directly from object files (*.o). Each port
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has an MD linker script, which does everything needed to be done at link
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time. As a result, they do from MI alignment restriction (read_mostly,
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cacheline_aligned) to load address specification for external boot loaders.
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Make this into multiple stages to make linkage more structural. Especially,
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reserve the final link for purely MD purpose. Note that in modular build,
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*.ko are shared between build of kernel and modular(9) modules (*.kmod).
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Monolithic build:
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*.o ---> netbsd.ko Generic MI linkage
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netbsd.ko ---> netbsd.ro Kernel MI linkage
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netbsd.ro ---> netbsd Kernel MD linkage
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Modular build (kernel):
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*.o ---> *.ko Generic + Per-module MI linkage
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*.ko ---> netbsd.ro Kernel MI linkage
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netbsd.ro ---> netbsd Kernel MD linkage
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Modular build (module):
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*.o ---> *.ko Generic + Per-module MI linkage
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*.ko ---> *.ro Modular MI linkage
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*.ro ---> *.kmod Modular MD linkage
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Genric MI linkage is for processing MI linkage that can be applied generally.
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Data section alignment (.data.read_mostly and .data.cacheline_aligned) is
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processed here.
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Per-module MI linkage is for modules that want some ordering. For example,
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machdep.ko wants to put entry code at the top of .text and .data.
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Kernel MI linkage is for collecting kernel global section data, that is what
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link-set is used for now. Once they are collected and symbols to the ranges
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are assigned, those sections are merged into the pre-existing sections
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(.rodata) because link-set sections in "netbsd" will never be interpreted by
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external loaders.
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Kernel MD linkage is used purely for MD purposes, that is, how kernels are
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loaded by external loaders. It might be possible that one kernel relocatable
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(netbsd.ro) is linked into multiple final kernel image (netbsd) for diferent
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load addresses.
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Modular MI linkage is to prepare a module to be loadable as modular(9). This
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may add some extra sections and/or symbols.
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Modular MD linkage is again for pure MD purposes like kernel MD linkage.
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Adjustment and/or optimization may be done.
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Kernel and modular MI linkages may change behavior depending on existence
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of debug information. In the future .symtab will be copied using linker
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during this stage.
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o Fix db_symtab copying (COPY_SYMTAB)
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o Collect all objects and create a relocatable (netbsd.ro). At this point,
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the number of symbols is known.
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o Relink and allocate .rodata.symtab with the calculated size of .symtab.
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Linker recalculates symbol addresses.
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o Embed the .symtab into .rodata.symtab.
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o Link the final netbsd ELF.
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The make(1) rule (dependency graph) should be identical with/without
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COPY_SYMTAB. Kill .ifdef COPY_SYMTAB from $S/conf/Makefile.kern.inc.
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o Preprocess and generate linker scripts dynamically.
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Include opt_xxx.h and replace some constant values (e.g. COHERENCY_UNIT,
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PAGE_SIZE, KERNEL_BASE_PHYS, KERNEL_BASE_VIRT, ...) with cpp(1).
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Don't unnecessarily define symbols. Don't use sed(1).
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o Clean up linker scripts.
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o Don't specify OUTPUT_FORMAT()/OUTPUT_ARCH()
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These are basically set in compilers/linkers. If non-default ABI is used,
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command-line arguments should be specified.
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o Remove .rel/.rela handlings.
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These are set in relocatable objects, and handled by dynamic linkers.
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Totally irrelefant for kernels.
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o Clean up debug section handlings.
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o Document (section boundary) symbols set in linker scripts.
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There must be a reason why symbols are defined and exported.
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PROVIDE() is to define internal symbols.
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o Clean up load addresses.
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o Program headers.
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o According to matt@, .ARM.extab/.ARM.exidx sections are no longer needed.
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o Redesign swapnetbsd.c (root/swap device specification)
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Don't build a whole kernel only to specify root/swap devices.
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Make these parameter re-configurable afterwards.
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o Namespace.
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Investigate namespace of attributes/modules/options. Figure out the hidden
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design about these, document it, then re-design it.
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At this moment, all of them share the single "selecttab", which means their
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namespaces are common, but they also have respective tables (attrtab,
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opttab, etc.).
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Selecting an option (addoption()), that is also a module name, works only if
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the module doesn't depend on anything, because addoption() doesn't select
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module and its dependencies (selectattr()). In other words, an option is
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only safely converted to a module (define), only if it doesn't depend on
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anything. (One example is DDB.)
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o Convert pseudo(dev) attach functions to take (void) (== kernel ctors).
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The pseudo attach function was originally designed to take `int n' as
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the number of instances of the pseudo device. Now most of pseudo
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devices have been converted to be `cloneable', meaning that their
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instances are dynamically allocated at run-time, because guessing how
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much instances are needed for users at compile time is almost impossible.
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Restricting such a pure software resource at compile time is senseless,
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considering that the rest of the world is dynamic.
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If pseudo attach functions once become (void), config(1) no longer
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has to generate iteration to call those functions, by making them part
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of kernel constructors, that are a list of (void) functions.
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Some pseudo devices may have dependency/ordering problems, because
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pseudo attach functions have no choice when to be called. This could
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be solved by converting to kctors, where functions are called in order
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by dependency.
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o Enhance ioconf behavior for pseudo-devices
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See "bin/48571: config(1) ioconf is insufficient for pseudo-devices" for
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more details. In a nutshell, it would be "useful" for config to emit
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the necessary stuff in the generated ioconf.[ch] to enable use of
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config_{init,fini}_component() for attaching and detaching pseudodev's.
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Currently, you need to manually construct your own data structures, and
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manually "attach" them, one at a time. This leads to duplication of
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code (where multiple drivers contain the same basic logic), and doesn't
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necessarily handle all of the "frobbing" of the kernel lists.
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o Don't use -Ttext ${TEXTADDR}.
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Although ld(1)'s `-Ttext ${TEXTADDR}' is an easy way to specify the virtual
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base address of .text at link time, it needs to change command-line; in
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kernel build, Makefile needs to change to reflect kernel's configuration.
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It is simpler to reflect kenel configuration using linker script via assym.h.
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o Convert ${DIAGNOSTIC} and ${DEBUG} as flags (defflag).
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Probably generate opt_diagnostic.h/opt_debug.h and include them in
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sys/param.h.
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o Strictly define DIAGNOSTIC.
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It is possible to make DIAGNOSTIC kernel and modules binary-compatible with
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non-DIAGNOSTIC ones. In that case, debug type informations should match
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theoretically (not confirmed).
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o Use suffix rules.
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Build objects following suffix rules. Source files are defined as relative to
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$S (e.g. sys/kern/init_main.c) and objects are generated in the corresponding
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subdirectories under kernel build directories (e.g.
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.../compile/GENERIC/sys/kern/init_main.o). Dig subdirectories from within
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config(1).
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Debugging (-g) and profiling (-pg) objects could be generated with *.go/*.po
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suffixes as userland libraries do. Maybe something similar for
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DIAGNOSTIC/DEBUG.
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genassym(1) definitions will be split into per-source instead of the single
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assym.h. Dependencies are corrected and some of misterious dependencies on
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`Makefile' in sys/conf/Makefile.kern.inc can go away.
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o Define genassym(1) symbols per file.
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Have each file define symbols that have to be generated by genassym(1) so
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that more accurate dependency is reflected.
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For example, if foo.S needs some symbols, it defines them in foo.assym,
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declaring that foo.S depends on foo.assym.h, and includes foo.assym.h.
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foo.assym.h is generated by following the suffix rule of .assym -> .assym.h.
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When one header is updated, only related *.assym.h files are regenerated,
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instead of rebuilding all MD/*.S files that depend on the global, single
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assym.h.
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o Support library.
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Provide a consistent way to build library either as .o or .a.
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Build libraries in sub-make. Don't include library makefiles. Don't
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pollute search path (.PATH). libkern does too much.
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o Accept `.a' suffix.
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Make "file" command accept `.a' suffix. Handle it the same way as `.o'.
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o Clean up ${MD_OBJS} and friends in Makefile.${MACHINE}.
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Don't use ${MD_OBJS}, ${MD_LIBS}, ${MD_SFILES}, and ${MD_CFILES}.
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List files in config(5)'s "file". Override build rules only when neccesary.
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Rely on the fact that config(1) parses files.${MACHINE} first, outputs
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files in the order it parses files.* (actually include depth), and
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`Makefile.kern.inc' preserve file order to pass to ${LD}.
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o Clean up CTF-related rules.
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Don't overwrite compile/link rules conditionally by existence of
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${CTFCONVERT}/${CTFMERGE}. Give a separate suffix (*.ctfo) and define its
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rules (.c -> .ctfo).
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o Consider using cpp -MD instead of ${MKDEP}.
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o Make "make depend" mandatory.
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Automatically execute "make depend".
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