xref: /openbmc/u-boot/tools/binman/README (revision 51cb23d4)
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
209Image description format
210------------------------
211
212The binman node is called 'binman'. An example image description is shown
213below:
214
215	binman {
216		filename = "u-boot-sunxi-with-spl.bin";
217		pad-byte = <0xff>;
218		blob {
219			filename = "spl/sunxi-spl.bin";
220		};
221		u-boot {
222			pos = <CONFIG_SPL_PAD_TO>;
223		};
224	};
225
226
227This requests binman to create an image file called u-boot-sunxi-with-spl.bin
228consisting of a specially formatted SPL (spl/sunxi-spl.bin, built by the
229normal U-Boot Makefile), some 0xff padding, and a U-Boot legacy image. The
230padding comes from the fact that the second binary is placed at
231CONFIG_SPL_PAD_TO. If that line were omitted then the U-Boot binary would
232immediately follow the SPL binary.
233
234The binman node describes an image. The sub-nodes describe entries in the
235image. Each entry represents a region within the overall image. The name of
236the entry (blob, u-boot) tells binman what to put there. For 'blob' we must
237provide a filename. For 'u-boot', binman knows that this means 'u-boot.bin'.
238
239Entries are normally placed into the image sequentially, one after the other.
240The image size is the total size of all entries. As you can see, you can
241specify the start position of an entry using the 'pos' property.
242
243Note that due to a device tree requirement, all entries must have a unique
244name. If you want to put the same binary in the image multiple times, you can
245use any unique name, with the 'type' property providing the type.
246
247The attributes supported for entries are described below.
248
249pos:
250	This sets the position of an entry within the image. The first byte
251	of the image is normally at position 0. If 'pos' is not provided,
252	binman sets it to the end of the previous region, or the start of
253	the image's entry area (normally 0) if there is no previous region.
254
255align:
256	This sets the alignment of the entry. The entry position is adjusted
257	so that the entry starts on an aligned boundary within the image. For
258	example 'align = <16>' means that the entry will start on a 16-byte
259	boundary. Alignment shold be a power of 2. If 'align' is not
260	provided, no alignment is performed.
261
262size:
263	This sets the size of the entry. The contents will be padded out to
264	this size. If this is not provided, it will be set to the size of the
265	contents.
266
267pad-before:
268	Padding before the contents of the entry. Normally this is 0, meaning
269	that the contents start at the beginning of the entry. This can be
270	offset the entry contents a little. Defaults to 0.
271
272pad-after:
273	Padding after the contents of the entry. Normally this is 0, meaning
274	that the entry ends at the last byte of content (unless adjusted by
275	other properties). This allows room to be created in the image for
276	this entry to expand later. Defaults to 0.
277
278align-size:
279	This sets the alignment of the entry size. For example, to ensure
280	that the size of an entry is a multiple of 64 bytes, set this to 64.
281	If 'align-size' is not provided, no alignment is performed.
282
283align-end:
284	This sets the alignment of the end of an entry. Some entries require
285	that they end on an alignment boundary, regardless of where they
286	start. If 'align-end' is not provided, no alignment is performed.
287
288	Note: This is not yet implemented in binman.
289
290filename:
291	For 'blob' types this provides the filename containing the binary to
292	put into the entry. If binman knows about the entry type (like
293	u-boot-bin), then there is no need to specify this.
294
295type:
296	Sets the type of an entry. This defaults to the entry name, but it is
297	possible to use any name, and then add (for example) 'type = "u-boot"'
298	to specify the type.
299
300
301The attributes supported for images are described below. Several are similar
302to those for entries.
303
304size:
305	Sets the image size in bytes, for example 'size = <0x100000>' for a
306	1MB image.
307
308align-size:
309	This sets the alignment of the image size. For example, to ensure
310	that the image ends on a 512-byte boundary, use 'align-size = <512>'.
311	If 'align-size' is not provided, no alignment is performed.
312
313pad-before:
314	This sets the padding before the image entries. The first entry will
315	be positionad after the padding. This defaults to 0.
316
317pad-after:
318	This sets the padding after the image entries. The padding will be
319	placed after the last entry. This defaults to 0.
320
321pad-byte:
322	This specifies the pad byte to use when padding in the image. It
323	defaults to 0. To use 0xff, you would add 'pad-byte = <0xff>'.
324
325filename:
326	This specifies the image filename. It defaults to 'image.bin'.
327
328sort-by-pos:
329	This causes binman to reorder the entries as needed to make sure they
330	are in increasing positional order. This can be used when your entry
331	order may not match the positional order. A common situation is where
332	the 'pos' properties are set by CONFIG options, so their ordering is
333	not known a priori.
334
335	This is a boolean property so needs no value. To enable it, add a
336	line 'sort-by-pos;' to your description.
337
338multiple-images:
339	Normally only a single image is generated. To create more than one
340	image, put this property in the binman node. For example, this will
341	create image1.bin containing u-boot.bin, and image2.bin containing
342	both spl/u-boot-spl.bin and u-boot.bin:
343
344	binman {
345		multiple-images;
346		image1 {
347			u-boot {
348			};
349		};
350
351		image2 {
352			spl {
353			};
354			u-boot {
355			};
356		};
357	};
358
359end-at-4gb:
360	For x86 machines the ROM positions start just before 4GB and extend
361	up so that the image finished at the 4GB boundary. This boolean
362	option can be enabled to support this. The image size must be
363	provided so that binman knows when the image should start. For an
364	8MB ROM, the position of the first entry would be 0xfff80000 with
365	this option, instead of 0 without this option.
366
367
368Examples of the above options can be found in the tests. See the
369tools/binman/test directory.
370
371
372Special properties
373------------------
374
375Some entries support special properties, documented here:
376
377u-boot-with-ucode-ptr:
378	optional-ucode: boolean property to make microcode optional. If the
379		u-boot.bin image does not include microcode, no error will
380		be generated.
381
382
383Order of image creation
384-----------------------
385
386Image creation proceeds in the following order, for each entry in the image.
387
3881. GetEntryContents() - the contents of each entry are obtained, normally by
389reading from a file. This calls the Entry.ObtainContents() to read the
390contents. The default version of Entry.ObtainContents() calls
391Entry.GetDefaultFilename() and then reads that file. So a common mechanism
392to select a file to read is to override that function in the subclass. The
393functions must return True when they have read the contents. Binman will
394retry calling the functions a few times if False is returned, allowing
395dependencies between the contents of different entries.
396
3972. GetEntryPositions() - calls Entry.GetPositions() for each entry. This can
398return a dict containing entries that need updating. The key should be the
399entry name and the value is a tuple (pos, size). This allows an entry to
400provide the position and size for other entries. The default implementation
401of GetEntryPositions() returns {}.
402
4033. PackEntries() - calls Entry.Pack() which figures out the position and
404size of an entry. The 'current' image position is passed in, and the function
405returns the position immediately after the entry being packed. The default
406implementation of Pack() is usually sufficient.
407
4084. CheckSize() - checks that the contents of all the entries fits within
409the image size. If the image does not have a defined size, the size is set
410large enough to hold all the entries.
411
4125. CheckEntries() - checks that the entries do not overlap, nor extend
413outside the image.
414
4156. ProcessEntryContents() - this calls Entry.ProcessContents() on each entry.
416The default implementatoin does nothing. This can be overriden to adjust the
417contents of an entry in some way. For example, it would be possible to create
418an entry containing a hash of the contents of some other entries. At this
419stage the position and size of entries should not be adjusted.
420
4217. BuildImage() - builds the image and writes it to a file. This is the final
422step.
423
424
425Automatic .dtsi inclusion
426-------------------------
427
428It is sometimes inconvenient to add a 'binman' node to the .dts file for each
429board. This can be done by using #include to bring in a common file. Another
430approach supported by the U-Boot build system is to automatically include
431a common header. You can then put the binman node (and anything else that is
432specific to U-Boot, such as u-boot,dm-pre-reloc properies) in that header
433file.
434
435Binman will search for the following files in arch/<arch>/dts:
436
437   <dts>-u-boot.dtsi where <dts> is the base name of the .dts file
438   <CONFIG_SYS_SOC>-u-boot.dtsi
439   <CONFIG_SYS_CPU>-u-boot.dtsi
440   <CONFIG_SYS_VENDOR>-u-boot.dtsi
441   u-boot.dtsi
442
443U-Boot will only use the first one that it finds. If you need to include a
444more general file you can do that from the more specific file using #include.
445If you are having trouble figuring out what is going on, you can uncomment
446the 'warning' line in scripts/Makefile.lib to see what it has found:
447
448   # Uncomment for debugging
449   # $(warning binman_dtsi_options: $(binman_dtsi_options))
450
451
452Code coverage
453-------------
454
455Binman is a critical tool and is designed to be very testable. Entry
456implementations target 100% test coverage. Run 'binman -T' to check this.
457
458To enable Python test coverage on Debian-type distributions (e.g. Ubuntu):
459
460   $ sudo apt-get install python-pip python-pytest
461   $ sudo pip install coverage
462
463
464Advanced Features / Technical docs
465----------------------------------
466
467The behaviour of entries is defined by the Entry class. All other entries are
468a subclass of this. An important subclass is Entry_blob which takes binary
469data from a file and places it in the entry. In fact most entry types are
470subclasses of Entry_blob.
471
472Each entry type is a separate file in the tools/binman/etype directory. Each
473file contains a class called Entry_<type> where <type> is the entry type.
474New entry types can be supported by adding new files in that directory.
475These will automatically be detected by binman when needed.
476
477Entry properties are documented in entry.py. The entry subclasses are free
478to change the values of properties to support special behaviour. For example,
479when Entry_blob loads a file, it sets content_size to the size of the file.
480Entry classes can adjust other entries. For example, an entry that knows
481where other entries should be positioned can set up those entries' positions
482so they don't need to be set in the binman decription. It can also adjust
483entry contents.
484
485Most of the time such essoteric behaviour is not needed, but it can be
486essential for complex images.
487
488
489History / Credits
490-----------------
491
492Binman takes a lot of inspiration from a Chrome OS tool called
493'cros_bundle_firmware', which I wrote some years ago. That tool was based on
494a reasonably simple and sound design but has expanded greatly over the
495years. In particular its handling of x86 images is convoluted.
496
497Quite a few lessons have been learned which are hopefully be applied here.
498
499
500Design notes
501------------
502
503On the face of it, a tool to create firmware images should be fairly simple:
504just find all the input binaries and place them at the right place in the
505image. The difficulty comes from the wide variety of input types (simple
506flat binaries containing code, packaged data with various headers), packing
507requirments (alignment, spacing, device boundaries) and other required
508features such as hierarchical images.
509
510The design challenge is to make it easy to create simple images, while
511allowing the more complex cases to be supported. For example, for most
512images we don't much care exactly where each binary ends up, so we should
513not have to specify that unnecessarily.
514
515New entry types should aim to provide simple usage where possible. If new
516core features are needed, they can be added in the Entry base class.
517
518
519To do
520-----
521
522Some ideas:
523- Fill out the device tree to include the final position and size of each
524  entry (since the input file may not always specify these)
525- Use of-platdata to make the information available to code that is unable
526  to use device tree (such as a very small SPL image)
527- Write an image map to a text file
528- Allow easy building of images by specifying just the board name
529- Produce a full Python binding for libfdt (for upstream)
530- Add an option to decode an image into the constituent binaries
531- Suppoort hierarchical images (packing of binaries into another binary
532  which is then placed in the image)
533- Support building an image for a board (-b) more completely, with a
534  configurable build directory
535- Consider making binman work with buildman, although if it is used in the
536  Makefile, this will be automatic
537- Implement align-end
538
539--
540Simon Glass <sjg@chromium.org>
5417/7/2016
542