[RFC PATCH 0/6] Clean up arm linker scripts

[Ilias Apalodimas]

On Wed, 28 Feb 2024 at 13:11, Peter Robinson <pbrobinson at gmail.com> wrote:
>
> On Wed, 28 Feb 2024 at 10:58, Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > 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].
> > This has led to confusion over the years, ending up with mixed section
> > definitions. Some sections being 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.
> >
> > I am not sure if this used to be a compiler bug, but 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
>
> Should we be setting/upping the minimum version of the linker version
> as part of this?

The patch that added those as C-defined variables, was in 2013. So any
linker that's not ancient history should emit those correctly.


>
> > 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")
> >
> > 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/qualcomm/dragonboard820c/u-boot.lds |  41 ++-----
> >  board/vscom/baltos/u-boot.lds             | 128 ----------------------
> >  include/asm-generic/sections.h            |   3 +
> >  lib/efi_loader/efi_runtime.c              |   1 +
> >  10 files changed, 58 insertions(+), 352 deletions(-)
> >  delete mode 100644 board/vscom/baltos/u-boot.lds
> >
> > --
> > 2.37.2
> >