On 2/28/24 04:15, Ilias Apalodimas wrote:
On Wed, 28 Feb 2024 at 13:11, Peter Robinson <pbrobin...@gmail.com> wrote:
On Wed, 28 Feb 2024 at 10:58, Ilias Apalodimas
<ilias.apalodi...@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.
GNU ld fixed the problem on 2016-02-23, with this entry in the bfd
changelog:
* elflink.c (bfd_elf_record_link_assignment): Check for shared
library, instead of PIC, and don't check PDE when making linker
assigned symbol dynamic.
It looks like the change was first included in binutils 2.27, released
2016-08-03. I don't know where the minimum linker version requirement is
memorialized but there's a good chance that U-Boot already requires a
version more recent than that. (Someone who knows where that is will
have to check.)
In either case, I strongly agree: sections.c is an unnecessary
workaround with any reasonably recent linker version, it's
fickle/incompatible with non-GNU linkers such as LLD, and the marker
symbols belong in the linker script. This patchset is a big step in the
right direction!
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
