Ilias Apalodimas <ilias.apalodimas@linaro.org> says:
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.
For both QEMU v7/v8 bloat-o-meter shows now size difference
$~ ./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%
The symbols seem largely unchanged apart from a difference in .bss
as well as the emited sections and object types of the affected variables.
On the output below the first value is from -next and the second comes from
-next + this patchset. The .bss_start/end sections have disappeared from
the newer binaries.
# For example on QEMU v8:
efi_runtime_start
7945: 0000000000000178 0 OBJECT GLOBAL DEFAULT 2 __efi_runtime_start
7942: 0000000000000178 0 NOTYPE GLOBAL DEFAULT 2 __efi_runtime_start
efi_runtime_stop
9050: 0000000000000d38 0 OBJECT GLOBAL DEFAULT 2 __efi_runtime_stop
9047: 0000000000000d38 0 NOTYPE GLOBAL DEFAULT 2 __efi_runtime_stop
__efi_runtime_rel_start
7172: 00000000000dc2f0 0 OBJECT GLOBAL DEFAULT 10 __efi_runtime_rel_start
7169: 00000000000dc2f0 0 NOTYPE GLOBAL DEFAULT 10 __efi_runtime_rel_start
__efi_runtime_rel_stop
7954: 00000000000dc4a0 0 OBJECT GLOBAL DEFAULT 10 __efi_runtime_rel_stop
7951: 00000000000dc4a0 0 NOTYPE GLOBAL DEFAULT 10 __efi_runtime_rel_stop
__rel_dyn_start
7030: 00000000000dc4a0 0 OBJECT GLOBAL DEFAULT 11 __rel_dyn_start
7027: 00000000000dc4a0 0 NOTYPE GLOBAL DEFAULT 11 __rel_dyn_start
__rel_dyn_end
8959: 0000000000102b10 0 OBJECT GLOBAL DEFAULT 12 __rel_dyn_end
8956: 0000000000102b10 0 NOTYPE GLOBAL DEFAULT 11 __rel_dyn_end
image_copy_start
9051: 0000000000000000 0 OBJECT GLOBAL DEFAULT 1 __image_copy_start
9048: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 1 __image_copy_start
image_copy_end
7467: 00000000000dc4a0 0 OBJECT GLOBAL DEFAULT 11 __image_copy_end
7464: 00000000000dc4a0 0 NOTYPE GLOBAL DEFAULT 11 __image_copy_end
bss_start
12: 0000000000102b10 0 SECTION LOCAL DEFAULT 12 .bss_start
8087: 0000000000000018 0 NOTYPE GLOBAL DEFAULT 1 _bss_start_ofs
8375: 0000000000102b10 0 OBJECT GLOBAL DEFAULT 12 __bss_start
8084: 0000000000000018 0 NOTYPE GLOBAL DEFAULT 1 _bss_start_ofs
8372: 0000000000102b10 0 NOTYPE GLOBAL DEFAULT 12 __bss_start
bss_end
14: 000000000010bc30 0 SECTION LOCAL DEFAULT 14 .bss_end
7683: 000000000010bc30 0 OBJECT GLOBAL DEFAULT 14 __bss_end
8479: 0000000000000020 0 NOTYPE GLOBAL DEFAULT 1 _bss_end_ofs
7680: 000000000010bbb0 0 NOTYPE GLOBAL DEFAULT 12 __bss_end
8476: 0000000000000020 0 NOTYPE GLOBAL DEFAULT 1 _bss_end_ofs
# For QEMU v7:
efi_runtime_start
10703: 000003bc 0 OBJECT GLOBAL DEFAULT 2 __efi_runtime_start
10699: 000003c0 0 NOTYPE GLOBAL DEFAULT 2 __efi_runtime_start
efi_runtime_stop
11796: 000012ec 0 OBJECT GLOBAL DEFAULT 2 __efi_runtime_stop
11792: 000012ec 0 NOTYPE GLOBAL DEFAULT 2 __efi_runtime_stop
__efi_runtime_rel_start
9937: 000c40dc 0 OBJECT GLOBAL DEFAULT 8 __efi_runtime_rel_start
9935: 000c40dc 0 NOTYPE GLOBAL DEFAULT 9 __efi_runtime_rel_start
__efi_runtime_rel_stop
10712: 000c41dc 0 OBJECT GLOBAL DEFAULT 10 __efi_runtime_rel_stop
10708: 000c41dc 0 NOTYPE GLOBAL DEFAULT 9 __efi_runtime_rel_stop
__rel_dyn_start
9791: 000c41dc 0 OBJECT GLOBAL DEFAULT 10 __rel_dyn_start
9789: 000c41dc 0 NOTYPE GLOBAL DEFAULT 10 __rel_dyn_start
__rel_dyn_end
11708: 000da5f4 0 OBJECT GLOBAL DEFAULT 10 __rel_dyn_end
11704: 000da5f4 0 NOTYPE GLOBAL DEFAULT 10 __rel_dyn_end
image_copy_start
448: 0000177c 0 NOTYPE LOCAL DEFAULT 3 _image_copy_start_ofs
11797: 00000000 0 OBJECT GLOBAL DEFAULT 1 __image_copy_start
445: 0000177c 0 NOTYPE LOCAL DEFAULT 3 _image_copy_start_ofs
11793: 00000000 0 NOTYPE GLOBAL DEFAULT 1 __image_copy_start
image_copy_end
450: 00001780 0 NOTYPE LOCAL DEFAULT 3 _image_copy_end_ofs
10225: 000c41dc 0 OBJECT GLOBAL DEFAULT 10 __image_copy_end
447: 00001780 0 NOTYPE LOCAL DEFAULT 3 _image_copy_end_ofs
10222: 000c41dc 0 NOTYPE GLOBAL DEFAULT 10 __image_copy_end
bss_start
11: 000c41dc 0 SECTION LOCAL DEFAULT 11 .bss_start
11124: 000c41dc 0 OBJECT GLOBAL DEFAULT 11 __bss_start
11120: 000c41dc 0 NOTYPE GLOBAL DEFAULT 11 __bss_start
bss_end
13: 000cbbf8 0 SECTION LOCAL DEFAULT 13 .bss_end
10442: 000cbbf8 0 OBJECT GLOBAL DEFAULT 13 __bss_end
10439: 000cbbf8 0 NOTYPE GLOBAL DEFAULT 11 __bss_end
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 3ebd1cbc49 ("arm: make __bss_start and __bss_end__ compiler-generated")
[1] binutils commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared object")
6e2228fb05