[U-Boot] [PATCH v4 0/6] Enable Thumb build for ARM platforms

[Allen Martin]

> Tom, Albert,
> 
> Does this series look good?

Hi Aneesh,

The assembly files (like arch/arm/cpu/armv7/start.S) are still compiled ARM 32 with this patch series, but they call into C files that are compiled -mthumb.  Shouldn't the branches be changed into thumb state changing branches (bx/blx) ?  In particular I'm looking at the call into board_init_f()

-Allen


> 
> On Thursday 08 March 2012 10:50 PM, Aneesh V wrote:
> > Thumb is an alternate instruction set available in many
> > ARM processors. Below is a detailed description from ARM
> > specs:
> >
> > "The Thumb instruction set is a re-encoded subset of the
> > ARM instruction set. Thumb instructions execute in their
> > own processor state, with the architecture defining the
> > mechanisms required to transition between ARM and Thumb
> > states. The key difference is that Thumb instructions are
> > half the size of ARM instructions(16 bits compared with 32
> > bits). Greater code density can usually be achieved by using
> > the Thumb instruction set in preference to the ARM instruction
> > set, at a cost of some reduction in performance"
> >
> > "In ARMv6T2, Thumb-2 technology is introduced. This technology
> > makes it possible to extend the original Thumb instruction set
> > with many 32-bit instructions. The range of 32-bit Thumb instructions
> > included in ARMv6T2 permits Thumb code to achieve performance
> > similar to ARM code, with code density better than that of earlier
> > Thumb code. From ARMv6T2, the ARM and Thumb instruction sets provide
> > almost identical functionality"
> >
> > This series adds Thumb support in U-Boot and enables it for
> > OMAP4. It also fixes issues faced while booting OMAP4 with
> > Thumb-2 images of U-Boot and SPL.
> >
> > Thumb mode is becoming increasingly relevant for U-Boot with
> > the advent of SPL. It's very important to keep SPL size smaller
> > considering the internal RAM size constraints on many platforms.
> > On OMAP4 the size reduction enables us to use SPL on secure devices
> > that have smaller internal RAM available for non-secure world.
> >
> > To enable support for new platforms you just need to add
> > CONFIG_SYS_THUMB_BUILD in your config file.
> >
> > Tool-chains tried:
> > 1. Sourcery G++ Lite 2010q1-202
> > arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2010q1-202) 4.4.1
> > GNU ld (Sourcery G++ Lite 2010q1-202) - binutils 2.19.51.20090709
> >
> > 2. Linaro 4.6-2012.01
> > arm-linux-gnueabi-gcc (crosstool-NG linaro-1.13.1-2012.01-20120125 -
> > 	Linaro GCC 2012.01) 4.6.3 20120105 (prerelease)
> > GNU ld (crosstool-NG linaro-1.13.1-2012.01-20120125 - Linaro GCC
> 2012.01) 2.22
> >
> > Code-size reduction:
> > Image		ARM build	Thumb build	% Reduction
> > u-boot.bin	190408		144676		24.01%
> > u-boot-spl.bin	33200		25096		24.40%
> >
> > Performance(timestamp just before the main loop):
> > ARM build	Thumb build	% Reduction
> > 898510us	878247us	-2.25%
> >
> > Performance actually improved marginally for the Thumb
> > build, maybe because of the reduced image sizes.
> >
> > Aneesh V (6):
> >    arm: adapt asm/linkage.h from Linux
> >    armv7: add appropriate headers for assembly functions
> >    ARM: enable Thumb build
> >    armv7: Use -march=armv7-a and thereby enable Thumb-2
> >    omap4+: Avoid using __attribute__ ((__packed__))
> >    OMAP4: enable Thumb build
> >
> >   README                                         |    8 +++++
> >   arch/arm/config.mk                             |   22 +++++++++----
> >   arch/arm/cpu/armv7/config.mk                   |    7 +++-
> >   arch/arm/cpu/armv7/mx5/lowlevel_init.S         |    5 ++-
> >   arch/arm/cpu/armv7/mx6/lowlevel_init.S         |    5 ++-
> >   arch/arm/cpu/armv7/omap-common/lowlevel_init.S |   14 ++++----
> >   arch/arm/cpu/armv7/omap-common/reset.S         |    5 ++-
> >   arch/arm/cpu/armv7/omap3/lowlevel_init.S       |   41 ++++++++++++--
> ---------
> >   arch/arm/cpu/armv7/s5pc1xx/cache.S             |   10 +++--
> >   arch/arm/cpu/armv7/s5pc1xx/reset.S             |    5 ++-
> >   arch/arm/cpu/armv7/start.S                     |   13 ++++---
> >   arch/arm/cpu/armv7/tegra2/lowlevel_init.S      |    5 ++-
> >   arch/arm/cpu/armv7/u8500/lowlevel.S            |    9 +++--
> >   arch/arm/include/asm/arch-omap4/mux_omap4.h    |    2 +-
> >   arch/arm/include/asm/arch-omap5/mux_omap5.h    |    2 +-
> >   arch/arm/include/asm/linkage.h                 |    7 ++++
> >   include/configs/omap4_common.h                 |    2 +
> >   include/linux/linkage.h                        |    7 +++-
> >   18 files changed, 106 insertions(+), 63 deletions(-)
> >   create mode 100644 arch/arm/include/asm/linkage.h
> >
> 
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