On Wed, 28 Feb 2024 at 13:11, Peter Robinson pbrobinson@gmail.com wrote:
On Wed, 28 Feb 2024 at 10:58, Ilias Apalodimas ilias.apalodimas@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