[U-Boot] [RFC PATCH v2 0/15] Provide a mechanism to avoid using #ifdef everywhere

[Simon Glass]

Many parts of the U-Boot code base are sprinkled with #ifdefs. This makes
different boards compile different versions of the source code, meaning
that we must build all boards to check for failures. It is easy to misspell
an #ifdef and there is not as much checking of this by the compiler. Multiple
dependent #ifdefs are harder to do than with if..then..else. Variable
declarations must be #idefed as well as the code that uses them, often much
later in the file/function. #ifdef indents don't match code indents and
have their own separate indent feature. Overall, excessive use of #idef
hurts readability and makes the code harder to modify and refactor. For
people coming newly into the code base, #ifdefs can be a big barrier.

The use of #ifdef in U-Boot has possibly got a little out of hand. In an
attempt to turn the tide, this series includes a patch which provides a way
to make CONFIG macros available to C code without using the preprocessor.
This makes it possible to use standard C conditional features such as
if/then instead of #ifdef. A README update exhorts compliance.

As an example of how to use this, this series replaces all but two #ifdefs
from the main code body of common/main.c, which has the dubious distinction
of having the most #ifdefs by at least one measure:

$ for f in $(find . -name *.c); do echo $(grep -c "ifdef" $f) $f; done \
	|sort -nr |head
57 ./common/main.c
57 ./arch/powerpc/cpu/mpc83xx/cpu_init.c
48 ./arch/powerpc/lib/board.c
46 ./drivers/video/cfb_console.c
40 ./drivers/mtd/cfi_flash.c
38 ./net/tftp.c
38 ./common/cmd_bootm.c
37 ./drivers/usb/host/ohci-hcd.c
36 ./drivers/fpga/ivm_core.c
35 ./drivers/usb/gadget/ether.c

Code size for this patch seems to be roughly neutral (below numbers are
average change in byte size for each region:

       x86: (3 boards)   text -1.3   data +1.3
   sandbox: (1 boards)   bss +16.0
      m68k: (50 boards)   text -4.2
   powerpc: (622 boards)   text +9.1   data +0.0   bss +1.9
        sh: (21 boards)   bss +2.5
     nios2: (3 boards)   text +24.0   data -1.3   bss +1.3
       arm: (285 boards)   spl/u-boot-spl:text +0.4   text -2.3   bss +5.5
     nds32: (3 boards)   text -29.3   bss +10.7

Note that a config_drop.h file is added - this defines all the CONFIGs
which are not used in any board config file. Without this, autoconf cannot
define the macros for this CONFIGs.

Compile time for main.c does not seem to be any different in my tests. The
time to perform the 'dep' step (which now creates autoconf.h) increases,
from about 2.8s to about 4.6s. This additional time is used to grep, sed
and sort the contents of all the header file in U-Boot. The time for an
incremental build is not affected.

It would be much more efficient to maintain a list of all available CONFIG
defines, but no such list exists at present.

Changes in v2:
- Split out changes to main.c into separate patches
- Fix up a few errors and comments in the original RFC
- Use autoconf_...() instead of config_...()
- Use autoconf_has_...() instead of config_..._enabled()
- Add a grep to the sed/sort pipe to speed up processing

Simon Glass (15):
  Implement autoconf header file
  at91: Correct CONFIG_AUTOBOOT_PROMPT definition for pm9263
  net: Add prototype for update_tftp, and use autoconf
  main: Separate out the two abortboot() functions
  main: Move boot_delay code into its own function
  main: Use autoconf for boot retry feature
  main: Remove CONFIG #ifdefs from the abortboot() code
  main: Use get/setenv_ulong()
  main: Use autoconf for boot_delay code
  main: Use autoconf for parser selection
  main: Use autoconf in command line reading
  main: Use autoconf in main_loop()
  main: Correct header order
  main: Add debug_parser() to avoid #ifdefs
  main: Add debug_bootkeys to avoid #ifdefs

 Makefile                      |  42 ++-
 README                        |  87 ++++-
 common/cmd_fitupd.c           |   3 +-
 common/main.c                 | 809 ++++++++++++++++++------------------------
 common/update.c               |  24 +-
 include/command.h             |   2 -
 include/common.h              |   9 +-
 include/config_drop.h         |  17 +
 include/configs/pm9263.h      |   2 +-
 include/fdt_support.h         |   4 +-
 include/hush.h                |   2 -
 include/menu.h                |   2 -
 include/net.h                 |   3 +
 tools/scripts/define2conf.sed |  37 ++
 tools/scripts/define2list.sed |  31 ++
 15 files changed, 579 insertions(+), 495 deletions(-)
 create mode 100644 include/config_drop.h
 create mode 100644 tools/scripts/define2conf.sed
 create mode 100644 tools/scripts/define2list.sed

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1.8.1.3