U-Boot has up until now built with -fpic for the MIPS architecture,
producing position independent code which uses indirection through a
global offset table, making relocation fairly straightforward as it
simply involves patching up GOT entries.
Using -fpic does however have some downsides. The biggest of these is
that generated code is bloated in various ways. For example, function
calls are indirected through the GOT & the t9 register:
8f998064 lw t9,-32668(gp)
0320f809 jalr t9
Without -fpic the call is simply:
0f803f01 jal be00fc04 <puts>
This is more compact & faster (due to the lack of the load & the
dependency the jump has on its result). It is also easier to read &
debug because the disassembly shows what function is being called,
rather than just an offset from gp which would then have to be looked up
in the ELF to discover the target function.
Another disadvantage of -fpic is that each function begins with a
sequence to calculate the value of the gp register, for example:
3c1c0004 lui gp,0x4
279c3384 addiu gp,gp,13188
0399e021 addu gp,gp,t9
Without using -fpic this sequence no longer appears at the start of each
function, reducing code size considerably.
This patch switches U-Boot from building with -fpic to building with
-fno-pic, in order to gain the benefits described above. The cost of
this is an extra step during the build process to extract relocation
data from the ELF & write it into a new .rel section in a compact
format, plus the added complexity of dealing with multiple types of
relocation rather than the single type that applied to the GOT. The
benefit is smaller, cleaner, more debuggable code. The relocate_code()
function is reimplemented in C to handle the new relocation scheme,
which also makes it easier to read & debug.
Taking maltael_defconfig as an example the size of u-boot.bin built
using the Codescape MIPS 2016.05-06 toolchain (gcc 4.9.2, binutils
2.24.90) shrinks from 254KiB to 224KiB.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: u-boot@lists.denx.de
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Tested-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
The relocate_code function was handling cache maintenance incorrectly.
It copied U-Boot to its new location, flushed the caches & then
proceeded to apply relocations & jump to the new code without flushing
the caches again. This is problematic as the instruction cache could
potentially have already fetched instructions that hadn't had relocs
applied.
Rework this to perform the flush_cache call using the code in the
original copy of U-Boot, after having applied relocations to the new
copy of U-Boot. The new U-Boot can then be jumped to safely once that
cache flush has been performed.
As part of this, since the old U-Boot is used up until after that cache
flush, complexity around loading values from the GOT using a jump & link
instruction & loads from a table is removed. Instead we can simply load
the needed values with PTR_LA fromt the original GOT.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Commit 79fd7e649e
MIPS: always keep all sections in u-boot ELF binary.
Always keep all sections in u-boot ELF binary. Move all unneeded
sections after _end to avoid allocating space in the final binary.
Also remove .deadcode section which is now obsolete.
removed section .deadcode because the original symptoms were not
visible anymore. Unfortuneatly the binutils bug still exists.
The size of .rel.dyn section is often bigger than needed for all
entries. But objcopy only allocates space as much as required for all
reloc entries. Thus there is a gap between the last entry and
__rel_dyn_end in u-boot.bin. If u-boot is booted from RAM (e.g. in
SPL scenarios) that area could contain garbage data which could lead
to CPU exceptions during relocation.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
The generic board code uses the __init_end symbol to calculate
monitor_flash_len. Define said symbol for MIPS, equivalent to
__image_copy_end which is used for the same purpose in
arch/mips/lib/board.c.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Always keep all sections in u-boot ELF binary. Move all unneeded
sections after _end to avoid allocating space in the final binary.
Also remove .deadcode section which is now obsolete.
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Refactor linker-generated array code so that symbols
which were previously linker-generated are now compiler-
generated. This causes relocation records of type
R_ARM_ABS32 to become R_ARM_RELATIVE, which makes
code which uses LGA able to run before relocation as
well as after.
Note: this affects more than ARM targets, as linker-
lists span possibly all target architectures, notably
PowerPC.
Conflicts:
arch/arm/cpu/arm926ejs/mxs/u-boot-spl.lds
arch/arm/cpu/arm926ejs/spear/u-boot-spl.lds
arch/arm/cpu/armv7/omap-common/u-boot-spl.lds
board/ait/cam_enc_4xx/u-boot-spl.lds
board/davinci/da8xxevm/u-boot-spl-da850evm.lds
board/davinci/da8xxevm/u-boot-spl-hawk.lds
board/vpac270/u-boot-spl.lds
Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
This section contain the table needed for dynamic
relocation. Also provide symbols for the relocation
code to access the table.
Discard all sections which are not needed in the final
ELF binary and U-Boot image. Section .dynsym cannot be
discarded or GNU ld crashes otherwise. This section
will be stripped by GNU objcpy in a later patch.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Use the newly introduced symbol __image_copy_end as end address for
relocation of U-Boot image. This is needed for dynamic relocation added
in later patches. This patch obsoletes the symbols uboot_end and
uboot_end_data which are removed.
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
This symbol is used in later patches as end address
for relocation of the U-Boot image into RAM.
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
These symbols are used in later patches for as addresses for
clearing the BSS area in the relocated U-Boot image.
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
The '__got_start' and '__got_end' symbols are used
only in the linker script to compute the value of
the 'num_got_entries' symbol.
Remove the symbols and use the SIZEOF(.got) command
to get the size of the .got section.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
The patch adds an unified linker script file which
can be used for all currently supported MIPS targets.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Xiangfu Liu <xiangfu@openmobilefree.net>
Acked-by: Stefan Roese <sr@denx.de>
