xref: /openbmc/u-boot/tools/binman/README (revision 445277b9)
1# Copyright (c) 2016 Google, Inc
2#
3# SPDX-License-Identifier:	GPL-2.0+
4#
5
6Introduction
7------------
8
9Firmware often consists of several components which must be packaged together.
10For example, we may have SPL, U-Boot, a device tree and an environment area
11grouped together and placed in MMC flash. When the system starts, it must be
12able to find these pieces.
13
14So far U-Boot has not provided a way to handle creating such images in a
15general way. Each SoC does what it needs to build an image, often packing or
16concatenating images in the U-Boot build system.
17
18Binman aims to provide a mechanism for building images, from simple
19SPL + U-Boot combinations, to more complex arrangements with many parts.
20
21
22What it does
23------------
24
25Binman reads your board's device tree and finds a node which describes the
26required image layout. It uses this to work out what to place where. The
27output file normally contains the device tree, so it is in principle possible
28to read an image and extract its constituent parts.
29
30
31Features
32--------
33
34So far binman is pretty simple. It supports binary blobs, such as 'u-boot',
35'spl' and 'fdt'. It supports empty entries (such as setting to 0xff). It can
36place entries at a fixed location in the image, or fit them together with
37suitable padding and alignment. It provides a way to process binaries before
38they are included, by adding a Python plug-in. The device tree is available
39to U-Boot at run-time so that the images can be interpreted.
40
41Binman does not yet update the device tree with the final location of
42everything when it is done. A simple C structure could be generated for
43constrained environments like SPL (using dtoc) but this is also not
44implemented.
45
46Binman can also support incorporating filesystems in the image if required.
47For example x86 platforms may use CBFS in some cases.
48
49Binman is intended for use with U-Boot but is designed to be general enough
50to be useful in other image-packaging situations.
51
52
53Motivation
54----------
55
56Packaging of firmware is quite a different task from building the various
57parts. In many cases the various binaries which go into the image come from
58separate build systems. For example, ARM Trusted Firmware is used on ARMv8
59devices but is not built in the U-Boot tree. If a Linux kernel is included
60in the firmware image, it is built elsewhere.
61
62It is of course possible to add more and more build rules to the U-Boot
63build system to cover these cases. It can shell out to other Makefiles and
64build scripts. But it seems better to create a clear divide between building
65software and packaging it.
66
67At present this is handled by manual instructions, different for each board,
68on how to create images that will boot. By turning these instructions into a
69standard format, we can support making valid images for any board without
70manual effort, lots of READMEs, etc.
71
72Benefits:
73- Each binary can have its own build system and tool chain without creating
74any dependencies between them
75- Avoids the need for a single-shot build: individual parts can be updated
76and brought in as needed
77- Provides for a standard image description available in the build and at
78run-time
79- SoC-specific image-signing tools can be accomodated
80- Avoids cluttering the U-Boot build system with image-building code
81- The image description is automatically available at run-time in U-Boot,
82SPL. It can be made available to other software also
83- The image description is easily readable (it's a text file in device-tree
84format) and permits flexible packing of binaries
85
86
87Terminology
88-----------
89
90Binman uses the following terms:
91
92- image - an output file containing a firmware image
93- binary - an input binary that goes into the image
94
95
96Relationship to FIT
97-------------------
98
99FIT is U-Boot's official image format. It supports multiple binaries with
100load / execution addresses, compression. It also supports verification
101through hashing and RSA signatures.
102
103FIT was originally designed to support booting a Linux kernel (with an
104optional ramdisk) and device tree chosen from various options in the FIT.
105Now that U-Boot supports configuration via device tree, it is possible to
106load U-Boot from a FIT, with the device tree chosen by SPL.
107
108Binman considers FIT to be one of the binaries it can place in the image.
109
110Where possible it is best to put as much as possible in the FIT, with binman
111used to deal with cases not covered by FIT. Examples include initial
112execution (since FIT itself does not have an executable header) and dealing
113with device boundaries, such as the read-only/read-write separation in SPI
114flash.
115
116For U-Boot, binman should not be used to create ad-hoc images in place of
117FIT.
118
119
120Relationship to mkimage
121-----------------------
122
123The mkimage tool provides a means to create a FIT. Traditionally it has
124needed an image description file: a device tree, like binman, but in a
125different format. More recently it has started to support a '-f auto' mode
126which can generate that automatically.
127
128More relevant to binman, mkimage also permits creation of many SoC-specific
129image types. These can be listed by running 'mkimage -T list'. Examples
130include 'rksd', the Rockchip SD/MMC boot format. The mkimage tool is often
131called from the U-Boot build system for this reason.
132
133Binman considers the output files created by mkimage to be binary blobs
134which it can place in an image. Binman does not replace the mkimage tool or
135this purpose. It would be possible in some situtions to create a new entry
136type for the images in mkimage, but this would not add functionality. It
137seems better to use the mkiamge tool to generate binaries and avoid blurring
138the boundaries between building input files (mkimage) and packaging then
139into a final image (binman).
140
141
142Example use of binman in U-Boot
143-------------------------------
144
145Binman aims to replace some of the ad-hoc image creation in the U-Boot
146build system.
147
148Consider sunxi. It has the following steps:
149
1501. It uses a custom mksunxiboot tool to build an SPL image called
151sunxi-spl.bin. This should probably move into mkimage.
152
1532. It uses mkimage to package U-Boot into a legacy image file (so that it can
154hold the load and execution address) called u-boot.img.
155
1563. It builds a final output image called u-boot-sunxi-with-spl.bin which
157consists of sunxi-spl.bin, some padding and u-boot.img.
158
159Binman is intended to replace the last step. The U-Boot build system builds
160u-boot.bin and sunxi-spl.bin. Binman can then take over creation of
161sunxi-spl.bin (by calling mksunxiboot, or hopefully one day mkimage). In any
162case, it would then create the image from the component parts.
163
164This simplifies the U-Boot Makefile somewhat, since various pieces of logic
165can be replaced by a call to binman.
166
167
168Example use of binman for x86
169-----------------------------
170
171In most cases x86 images have a lot of binary blobs, 'black-box' code
172provided by Intel which must be run for the platform to work. Typically
173these blobs are not relocatable and must be placed at fixed areas in the
174firmare image.
175
176Currently this is handled by ifdtool, which places microcode, FSP, MRC, VGA
177BIOS, reference code and Intel ME binaries into a u-boot.rom file.
178
179Binman is intended to replace all of this, with ifdtool left to handle only
180the configuration of the Intel-format descriptor.
181
182
183Running binman
184--------------
185
186Type:
187
188	binman -b <board_name>
189
190to build an image for a board. The board name is the same name used when
191configuring U-Boot (e.g. for sandbox_defconfig the board name is 'sandbox').
192Binman assumes that the input files for the build are in ../b/<board_name>.
193
194Or you can specify this explicitly:
195
196	binman -I <build_path>
197
198where <build_path> is the build directory containing the output of the U-Boot
199build.
200
201(Future work will make this more configurable)
202
203In either case, binman picks up the device tree file (u-boot.dtb) and looks
204for its instructions in the 'binman' node.
205
206Binman has a few other options which you can see by running 'binman -h'.
207
208
209Enabling binman for a board
210---------------------------
211
212At present binman is invoked from a rule in the main Makefile. Typically you
213will have a rule like:
214
215ifneq ($(CONFIG_ARCH_<something>),)
216u-boot-<your_suffix>.bin: <input_file_1> <input_file_2> checkbinman FORCE
217	$(call if_changed,binman)
218endif
219
220This assumes that u-boot-<your_suffix>.bin is a target, and is the final file
221that you need to produce. You can make it a target by adding it to ALL-y
222either in the main Makefile or in a config.mk file in your arch subdirectory.
223
224Once binman is executed it will pick up its instructions from a device-tree
225file, typically <soc>-u-boot.dtsi, where <soc> is your CONFIG_SYS_SOC value.
226You can use other, more specific CONFIG options - see 'Automatic .dtsi
227inclusion' below.
228
229
230Image description format
231------------------------
232
233The binman node is called 'binman'. An example image description is shown
234below:
235
236	binman {
237		filename = "u-boot-sunxi-with-spl.bin";
238		pad-byte = <0xff>;
239		blob {
240			filename = "spl/sunxi-spl.bin";
241		};
242		u-boot {
243			pos = <CONFIG_SPL_PAD_TO>;
244		};
245	};
246
247
248This requests binman to create an image file called u-boot-sunxi-with-spl.bin
249consisting of a specially formatted SPL (spl/sunxi-spl.bin, built by the
250normal U-Boot Makefile), some 0xff padding, and a U-Boot legacy image. The
251padding comes from the fact that the second binary is placed at
252CONFIG_SPL_PAD_TO. If that line were omitted then the U-Boot binary would
253immediately follow the SPL binary.
254
255The binman node describes an image. The sub-nodes describe entries in the
256image. Each entry represents a region within the overall image. The name of
257the entry (blob, u-boot) tells binman what to put there. For 'blob' we must
258provide a filename. For 'u-boot', binman knows that this means 'u-boot.bin'.
259
260Entries are normally placed into the image sequentially, one after the other.
261The image size is the total size of all entries. As you can see, you can
262specify the start position of an entry using the 'pos' property.
263
264Note that due to a device tree requirement, all entries must have a unique
265name. If you want to put the same binary in the image multiple times, you can
266use any unique name, with the 'type' property providing the type.
267
268The attributes supported for entries are described below.
269
270pos:
271	This sets the position of an entry within the image. The first byte
272	of the image is normally at position 0. If 'pos' is not provided,
273	binman sets it to the end of the previous region, or the start of
274	the image's entry area (normally 0) if there is no previous region.
275
276align:
277	This sets the alignment of the entry. The entry position is adjusted
278	so that the entry starts on an aligned boundary within the image. For
279	example 'align = <16>' means that the entry will start on a 16-byte
280	boundary. Alignment shold be a power of 2. If 'align' is not
281	provided, no alignment is performed.
282
283size:
284	This sets the size of the entry. The contents will be padded out to
285	this size. If this is not provided, it will be set to the size of the
286	contents.
287
288pad-before:
289	Padding before the contents of the entry. Normally this is 0, meaning
290	that the contents start at the beginning of the entry. This can be
291	offset the entry contents a little. Defaults to 0.
292
293pad-after:
294	Padding after the contents of the entry. Normally this is 0, meaning
295	that the entry ends at the last byte of content (unless adjusted by
296	other properties). This allows room to be created in the image for
297	this entry to expand later. Defaults to 0.
298
299align-size:
300	This sets the alignment of the entry size. For example, to ensure
301	that the size of an entry is a multiple of 64 bytes, set this to 64.
302	If 'align-size' is not provided, no alignment is performed.
303
304align-end:
305	This sets the alignment of the end of an entry. Some entries require
306	that they end on an alignment boundary, regardless of where they
307	start. If 'align-end' is not provided, no alignment is performed.
308
309	Note: This is not yet implemented in binman.
310
311filename:
312	For 'blob' types this provides the filename containing the binary to
313	put into the entry. If binman knows about the entry type (like
314	u-boot-bin), then there is no need to specify this.
315
316type:
317	Sets the type of an entry. This defaults to the entry name, but it is
318	possible to use any name, and then add (for example) 'type = "u-boot"'
319	to specify the type.
320
321
322The attributes supported for images are described below. Several are similar
323to those for entries.
324
325size:
326	Sets the image size in bytes, for example 'size = <0x100000>' for a
327	1MB image.
328
329align-size:
330	This sets the alignment of the image size. For example, to ensure
331	that the image ends on a 512-byte boundary, use 'align-size = <512>'.
332	If 'align-size' is not provided, no alignment is performed.
333
334pad-before:
335	This sets the padding before the image entries. The first entry will
336	be positionad after the padding. This defaults to 0.
337
338pad-after:
339	This sets the padding after the image entries. The padding will be
340	placed after the last entry. This defaults to 0.
341
342pad-byte:
343	This specifies the pad byte to use when padding in the image. It
344	defaults to 0. To use 0xff, you would add 'pad-byte = <0xff>'.
345
346filename:
347	This specifies the image filename. It defaults to 'image.bin'.
348
349sort-by-pos:
350	This causes binman to reorder the entries as needed to make sure they
351	are in increasing positional order. This can be used when your entry
352	order may not match the positional order. A common situation is where
353	the 'pos' properties are set by CONFIG options, so their ordering is
354	not known a priori.
355
356	This is a boolean property so needs no value. To enable it, add a
357	line 'sort-by-pos;' to your description.
358
359multiple-images:
360	Normally only a single image is generated. To create more than one
361	image, put this property in the binman node. For example, this will
362	create image1.bin containing u-boot.bin, and image2.bin containing
363	both spl/u-boot-spl.bin and u-boot.bin:
364
365	binman {
366		multiple-images;
367		image1 {
368			u-boot {
369			};
370		};
371
372		image2 {
373			spl {
374			};
375			u-boot {
376			};
377		};
378	};
379
380end-at-4gb:
381	For x86 machines the ROM positions start just before 4GB and extend
382	up so that the image finished at the 4GB boundary. This boolean
383	option can be enabled to support this. The image size must be
384	provided so that binman knows when the image should start. For an
385	8MB ROM, the position of the first entry would be 0xfff80000 with
386	this option, instead of 0 without this option.
387
388
389Examples of the above options can be found in the tests. See the
390tools/binman/test directory.
391
392
393Special properties
394------------------
395
396Some entries support special properties, documented here:
397
398u-boot-with-ucode-ptr:
399	optional-ucode: boolean property to make microcode optional. If the
400		u-boot.bin image does not include microcode, no error will
401		be generated.
402
403
404Order of image creation
405-----------------------
406
407Image creation proceeds in the following order, for each entry in the image.
408
4091. GetEntryContents() - the contents of each entry are obtained, normally by
410reading from a file. This calls the Entry.ObtainContents() to read the
411contents. The default version of Entry.ObtainContents() calls
412Entry.GetDefaultFilename() and then reads that file. So a common mechanism
413to select a file to read is to override that function in the subclass. The
414functions must return True when they have read the contents. Binman will
415retry calling the functions a few times if False is returned, allowing
416dependencies between the contents of different entries.
417
4182. GetEntryPositions() - calls Entry.GetPositions() for each entry. This can
419return a dict containing entries that need updating. The key should be the
420entry name and the value is a tuple (pos, size). This allows an entry to
421provide the position and size for other entries. The default implementation
422of GetEntryPositions() returns {}.
423
4243. PackEntries() - calls Entry.Pack() which figures out the position and
425size of an entry. The 'current' image position is passed in, and the function
426returns the position immediately after the entry being packed. The default
427implementation of Pack() is usually sufficient.
428
4294. CheckSize() - checks that the contents of all the entries fits within
430the image size. If the image does not have a defined size, the size is set
431large enough to hold all the entries.
432
4335. CheckEntries() - checks that the entries do not overlap, nor extend
434outside the image.
435
4366. ProcessEntryContents() - this calls Entry.ProcessContents() on each entry.
437The default implementatoin does nothing. This can be overriden to adjust the
438contents of an entry in some way. For example, it would be possible to create
439an entry containing a hash of the contents of some other entries. At this
440stage the position and size of entries should not be adjusted.
441
4426. WriteEntryInfo()
443
4447. BuildImage() - builds the image and writes it to a file. This is the final
445step.
446
447
448Automatic .dtsi inclusion
449-------------------------
450
451It is sometimes inconvenient to add a 'binman' node to the .dts file for each
452board. This can be done by using #include to bring in a common file. Another
453approach supported by the U-Boot build system is to automatically include
454a common header. You can then put the binman node (and anything else that is
455specific to U-Boot, such as u-boot,dm-pre-reloc properies) in that header
456file.
457
458Binman will search for the following files in arch/<arch>/dts:
459
460   <dts>-u-boot.dtsi where <dts> is the base name of the .dts file
461   <CONFIG_SYS_SOC>-u-boot.dtsi
462   <CONFIG_SYS_CPU>-u-boot.dtsi
463   <CONFIG_SYS_VENDOR>-u-boot.dtsi
464   u-boot.dtsi
465
466U-Boot will only use the first one that it finds. If you need to include a
467more general file you can do that from the more specific file using #include.
468If you are having trouble figuring out what is going on, you can uncomment
469the 'warning' line in scripts/Makefile.lib to see what it has found:
470
471   # Uncomment for debugging
472   # This shows all the files that were considered and the one that we chose.
473   # u_boot_dtsi_options_debug = $(u_boot_dtsi_options_raw)
474
475
476Access to binman entry positions at run time
477--------------------------------------------
478
479Binman assembles images and determines where each entry is placed in the image.
480This information may be useful to U-Boot at run time. For example, in SPL it
481is useful to be able to find the location of U-Boot so that it can be executed
482when SPL is finished.
483
484Binman allows you to declare symbols in the SPL image which are filled in
485with their correct values during the build. For example:
486
487    binman_sym_declare(ulong, u_boot_any, pos);
488
489declares a ulong value which will be assigned to the position of any U-Boot
490image (u-boot.bin, u-boot.img, u-boot-nodtb.bin) that is present in the image.
491You can access this value with something like:
492
493    ulong u_boot_pos = binman_sym(ulong, u_boot_any, pos);
494
495Thus u_boot_pos will be set to the position of U-Boot in memory, assuming that
496the whole image has been loaded, or is available in flash. You can then jump to
497that address to start U-Boot.
498
499At present this feature is only supported in SPL. In principle it is possible
500to fill in such symbols in U-Boot proper, as well.
501
502
503Code coverage
504-------------
505
506Binman is a critical tool and is designed to be very testable. Entry
507implementations target 100% test coverage. Run 'binman -T' to check this.
508
509To enable Python test coverage on Debian-type distributions (e.g. Ubuntu):
510
511   $ sudo apt-get install python-pip python-pytest
512   $ sudo pip install coverage
513
514
515Advanced Features / Technical docs
516----------------------------------
517
518The behaviour of entries is defined by the Entry class. All other entries are
519a subclass of this. An important subclass is Entry_blob which takes binary
520data from a file and places it in the entry. In fact most entry types are
521subclasses of Entry_blob.
522
523Each entry type is a separate file in the tools/binman/etype directory. Each
524file contains a class called Entry_<type> where <type> is the entry type.
525New entry types can be supported by adding new files in that directory.
526These will automatically be detected by binman when needed.
527
528Entry properties are documented in entry.py. The entry subclasses are free
529to change the values of properties to support special behaviour. For example,
530when Entry_blob loads a file, it sets content_size to the size of the file.
531Entry classes can adjust other entries. For example, an entry that knows
532where other entries should be positioned can set up those entries' positions
533so they don't need to be set in the binman decription. It can also adjust
534entry contents.
535
536Most of the time such essoteric behaviour is not needed, but it can be
537essential for complex images.
538
539If you need to specify a particular device-tree compiler to use, you can define
540the DTC environment variable. This can be useful when the system dtc is too
541old.
542
543
544History / Credits
545-----------------
546
547Binman takes a lot of inspiration from a Chrome OS tool called
548'cros_bundle_firmware', which I wrote some years ago. That tool was based on
549a reasonably simple and sound design but has expanded greatly over the
550years. In particular its handling of x86 images is convoluted.
551
552Quite a few lessons have been learned which are hopefully be applied here.
553
554
555Design notes
556------------
557
558On the face of it, a tool to create firmware images should be fairly simple:
559just find all the input binaries and place them at the right place in the
560image. The difficulty comes from the wide variety of input types (simple
561flat binaries containing code, packaged data with various headers), packing
562requirments (alignment, spacing, device boundaries) and other required
563features such as hierarchical images.
564
565The design challenge is to make it easy to create simple images, while
566allowing the more complex cases to be supported. For example, for most
567images we don't much care exactly where each binary ends up, so we should
568not have to specify that unnecessarily.
569
570New entry types should aim to provide simple usage where possible. If new
571core features are needed, they can be added in the Entry base class.
572
573
574To do
575-----
576
577Some ideas:
578- Fill out the device tree to include the final position and size of each
579  entry (since the input file may not always specify these). See also
580  'Access to binman entry positions at run time' above
581- Use of-platdata to make the information available to code that is unable
582  to use device tree (such as a very small SPL image)
583- Write an image map to a text file
584- Allow easy building of images by specifying just the board name
585- Produce a full Python binding for libfdt (for upstream)
586- Add an option to decode an image into the constituent binaries
587- Suppoort hierarchical images (packing of binaries into another binary
588  which is then placed in the image)
589- Support building an image for a board (-b) more completely, with a
590  configurable build directory
591- Consider making binman work with buildman, although if it is used in the
592  Makefile, this will be automatic
593- Implement align-end
594
595--
596Simon Glass <sjg@chromium.org>
5977/7/2016
598