On 3/4/24 02:01, Ilias Apalodimas wrote:
commit 3ebd1cbc49f0 ("arm: make __bss_start and __bss_end__ compiler-generated")
and
commit f84a7b8f54db ("ARM: Fix __bss_start and __bss_end in linker scripts")
were moving the bss_start/end on c generated variables that were
injected in their own sections. The reason was that we needed relative
relocations for position independent code and linker bugs back then
prevented us from doing so.
However, the linker documentation pages states that symbols that are
defined within a section definition will create a relocatable
type with the value being a fixed offset from the base of a section.
This have been fixed since 2016 [1]. So let's start cleaning this up
starting with the bss_start and bss_end variables. Convert them into
symbols within the .bss section definition.
[0] https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_mono/ld.html#SEC13
[1] commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared
object")
Signed-off-by: Ilias Apalodimas <ilias.apalodi...@linaro.org>
Tested-by: Caleb Connolly <caleb.conno...@linaro.org> # Qualcomm sdm845
---
arch/arm/cpu/armv8/u-boot-spl.lds | 14 +++-----------
arch/arm/cpu/armv8/u-boot.lds | 15 +++------------
arch/arm/cpu/u-boot.lds | 22 ++++------------------
arch/arm/lib/sections.c | 2 --
arch/arm/mach-rockchip/u-boot-tpl-v8.lds | 14 +++-----------
arch/arm/mach-zynq/u-boot.lds | 21 +++------------------
6 files changed, 16 insertions(+), 72 deletions(-)
diff --git a/arch/arm/cpu/armv8/u-boot-spl.lds
b/arch/arm/cpu/armv8/u-boot-spl.lds
index 7cb9d731246d..16fddb46e9cb 100644
--- a/arch/arm/cpu/armv8/u-boot-spl.lds
+++ b/arch/arm/cpu/armv8/u-boot-spl.lds
@@ -63,18 +63,10 @@ SECTIONS
_image_binary_end = .;
- .bss_start (NOLOAD) : {
- . = ALIGN(8);
- KEEP(*(.__bss_start));
- } >.sdram
-
- .bss (NOLOAD) : {
+ .bss : {
+ __bss_start = .;
*(.bss*)
- . = ALIGN(8);
- } >.sdram
-
- .bss_end (NOLOAD) : {
- KEEP(*(.__bss_end));
+ __bss_end = .;
} >.sdram
/DISCARD/ : { *(.rela*) }
diff --git a/arch/arm/cpu/armv8/u-boot.lds b/arch/arm/cpu/armv8/u-boot.lds
index fb6a30c922f7..c4ee10ebc3ff 100644
--- a/arch/arm/cpu/armv8/u-boot.lds
+++ b/arch/arm/cpu/armv8/u-boot.lds
@@ -149,19 +149,10 @@ SECTIONS
_end = .;
- . = ALIGN(8);
-
- .bss_start : {
- KEEP(*(.__bss_start));
- }
-
- .bss : {
+ .bss ALIGN(8): {
+ __bss_start = .;
*(.bss*)
- . = ALIGN(8);
- }
-
- .bss_end : {
- KEEP(*(.__bss_end));
+ __bss_end = .;
}
/DISCARD/ : { *(.dynsym) }
diff --git a/arch/arm/cpu/u-boot.lds b/arch/arm/cpu/u-boot.lds
index 7724c9332c3b..90d329b1ebe0 100644
--- a/arch/arm/cpu/u-boot.lds
+++ b/arch/arm/cpu/u-boot.lds
@@ -206,27 +206,13 @@ SECTIONS
*(.mmutable)
}
-/*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
- */
-
- .bss_start __rel_dyn_start (OVERLAY) : {
- KEEP(*(.__bss_start));
- __bss_base = .;
- }
-
- .bss __bss_base (OVERLAY) : {
+ .bss ALIGN(4): {
Hi Ilias,
I have been reviewing this patchset by diffing output binaries and
linker maps between successive patches. Most of the patches in this
series result in no change to the output binary whatsoever (which also
means, no regressions!) but this one does have a change: .bss is being
moved after .mmutable. You should be able to see this yourself by
comparing `u-boot.map` after a successful build, before and after
applying this patch.
Since the current u-boot.lds puts .bss right after __image_copy_end
(which makes sense) and uses OVERLAY to overlap .rel.dyn (which... I
guess makes sense, if U-Boot zero-initializes .bss after applying
relocations), perhaps this patch should be moving the .bss section up
there in the .lds, putting (OVERLAY) back, and adding a comment to the
effect of "These sections occupy the same memory, but their lifetimes do
not overlap: U-Boot initializes .bss only after applying relocations and
therefore after it doesn't need .rel.dyn any more."
We might also decide that the overlay memory-saving trick isn't actually
all that important anymore and that .bss should have a new home. Someone
far more seasoned than I should be the one to make that decision though.
The rest of the patchset looks great! I'll add my tags to those in a bit.
Cheers,
Sam
+ __bss_start = .;
*(.bss*)
- . = ALIGN(4);
- __bss_limit = .;
- }
-
- .bss_end __bss_limit (OVERLAY) : {
- KEEP(*(.__bss_end));
+ __bss_end = .;
}
- .dynsym _image_binary_end : { *(.dynsym) }
+ .dynsym : { *(.dynsym) }
.dynbss : { *(.dynbss) }
.dynstr : { *(.dynstr*) }
.dynamic : { *(.dynamic*) }
diff --git a/arch/arm/lib/sections.c b/arch/arm/lib/sections.c
index 857879711c6a..8e8bd5797e16 100644
--- a/arch/arm/lib/sections.c
+++ b/arch/arm/lib/sections.c
@@ -19,8 +19,6 @@
* aliasing warnings.
*/
-char __bss_start[0] __section(".__bss_start");
-char __bss_end[0] __section(".__bss_end");
char __image_copy_start[0] __section(".__image_copy_start");
char __image_copy_end[0] __section(".__image_copy_end");
char __rel_dyn_start[0] __section(".__rel_dyn_start");
diff --git a/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
b/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
index 74618eba591b..b7887194026e 100644
--- a/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
+++ b/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
@@ -56,18 +56,10 @@ SECTIONS
_image_binary_end = .;
- .bss_start (NOLOAD) : {
- . = ALIGN(8);
- KEEP(*(.__bss_start));
- }
-
- .bss (NOLOAD) : {
+ .bss ALIGN(8) : {
+ __bss_start = .;
*(.bss*)
- . = ALIGN(8);
- }
-
- .bss_end (NOLOAD) : {
- KEEP(*(.__bss_end));
+ __bss_end = .;
}
/DISCARD/ : { *(.dynsym) }
diff --git a/arch/arm/mach-zynq/u-boot.lds b/arch/arm/mach-zynq/u-boot.lds
index 3b7c9d515f8b..8d3259821719 100644
--- a/arch/arm/mach-zynq/u-boot.lds
+++ b/arch/arm/mach-zynq/u-boot.lds
@@ -102,26 +102,11 @@ SECTIONS
_image_binary_end = .;
-/*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
- */
-
- .bss_start __rel_dyn_start (OVERLAY) : {
- KEEP(*(.__bss_start));
- __bss_base = .;
- }
-
- .bss __bss_base (OVERLAY) : {
+ .bss ALIGN(4): {
+ __bss_start = .;
*(.bss*)
- . = ALIGN(8);
- __bss_limit = .;
- }
-
- .bss_end __bss_limit (OVERLAY) : {
- KEEP(*(.__bss_end));
+ __bss_end = .;
}
-
/*
* Zynq needs to discard these sections because the user
* is expected to pass this image on to tools for boot.bin
