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[0/6] Clean up arm linker scripts

Message ID 20240304090113.1410575-1-ilias.apalodimas@linaro.org
Headers show
Series Clean up arm linker scripts | expand

Message

Ilias Apalodimas March 4, 2024, 9:01 a.m. UTC 
The arm linker scripts had a mix of symbols and C defined variables in an
effort to emit relative references instead of absolute ones e.g [0]. A
linker bug prevented us from doing so [1] -- fixed since 2016.
This has led to confusion over the years, ending up with mixed section
definitions. Some sections are defined with overlays and different
definitions between v7 and v8 architectures.
For example __efi_runtime_rel_start/end is defined as a linker symbol for
armv8 and a C variable in armv7.

Linker scripts nowadays can emit relative references, as long as the symbol
definition is contained within the section definition. So let's switch most
of the C defined variables and clean up the arm sections.c file.
There's still a few symbols remaining -- __secure_start/end,
__secure_stack_start/end and __end which can be cleaned up
in a followup series.

The resulting binary (tested in QEMU v7/v8) had no size differences apart from
the emited sections and object types of those variables. I've also added prints
throughout the U-Boot init sequence. The offsets and delta for 'end - start'
section sizes is unchanged.

For example on QEMU v8:
$~ ./scripts/bloat-o-meter u-boot u-boot.new
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
Function                                     old     new   delta
Total: Before=798861, After=798861, chg +0.00%

$~ readelf -sW u-boot | grep bss_s
    12: 00000000001029b8     0 SECTION LOCAL  DEFAULT   12 .bss_start
  8088: 0000000000000018     0 NOTYPE  GLOBAL DEFAULT    1 _bss_start_ofs
  8376: 00000000001029b8     0 OBJECT  GLOBAL DEFAULT   12 __bss_start
$~ readelf -sW u-boot.new | grep bss_s
  8085: 0000000000000018     0 NOTYPE  GLOBAL DEFAULT    1 _bss_start_ofs
  8373: 00000000001029b8     0 NOTYPE  GLOBAL DEFAULT   12 __bss_start

For QEMU v7 the differences are a bit bigger but only affect the variables
placed in the .bss section because that was defined as an OVERLAY in the
existing linker script.
For example:
$~ nm u-boot | grep tftp_prev_block
000ca0dc ? tftp_prev_block
$~ nm u-boot.new | grep tftp_prev_block
000e0a5c b tftp_prev_block -----> The symbol is now placed into .bss

It's worth noting that since the efi regions are affected by the change, booting
with EFI is preferable while testing. Booting the kernel only should be enough
since the efi stub and the kernel proper do request boottime and runtime
services respectively.
Something along the lines of
> virtio scan && load virtio 0 $kernel_addr_r Image && bootefi $kernel_addr_r
will work for QEMU aarch64.

Tested platforms:
- QEMU aarch64
- Xilinx kv260 kria starter kit & zynq
- QEMU armv7
- STM32MP157C-DK2

[0] commit 3ebd1cbc49f0 ("arm: make __bss_start and __bss_end__ compiler-generated")
[1] binutils commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared object")

Ilias Apalodimas (6):
  arm: baltos: remove custom linker script
  arm: clean up v7 and v8 linker scripts for bss_start/end
  arm: fix __efi_runtime_rel_start/end definitions
  arm: clean up v7 and v8 linker scripts for __rel_dyn_start/end
  arm: fix __efi_runtime_start/end definitions
  arm: move image_copy_start/end to linker symbols

 arch/arm/cpu/armv8/u-boot-spl.lds        |  14 +--
 arch/arm/cpu/armv8/u-boot.lds            |  45 ++------
 arch/arm/cpu/u-boot.lds                  |  74 +++----------
 arch/arm/lib/sections.c                  |  10 --
 arch/arm/mach-rockchip/u-boot-tpl-v8.lds |  22 +---
 arch/arm/mach-zynq/u-boot.lds            |  72 +++----------
 board/vscom/baltos/u-boot.lds            | 128 -----------------------
 include/asm-generic/sections.h           |   3 +
 lib/efi_loader/efi_runtime.c             |   1 +
 9 files changed, 50 insertions(+), 319 deletions(-)
 delete mode 100644 board/vscom/baltos/u-boot.lds

--

Changes since RFC:
- Rebase on top of -next and get rid of the dragonboard linker script changes.
  Caleb removed that file completely
- Rewrite some commit messages to include the binutils bug details (thanks Sam)

2.37.2