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arch/avr: reworked eliminating unused sections with GCC

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After a mailing list suggestion, the indirection that enabled
ARCH_TOOLCHAIN_GCC only when user requested it is removed.

The indirection was a safety measure for chips and boards with linker
scripts that (possibly) do not handle keeping for example .vectors
section even if the linker considers it unreferenced.

Instead, all existing configurations now disable
CONFIG_DEBUG_OPT_UNUSED_SECTIONS to prevent the linker from removing
any code. (Preserving previous behaviour.) This can be removed again
at some point after making sure that corresponding linker script
only removes code that is truly unused.

Signed-off-by: Kerogit <kr.git@kerogit.eu>
This commit is contained in:
Kerogit
2025-04-13 11:20:17 +02:00
committed by Xiang Xiao
parent 034d76f28f
commit 8126a8119f
18 changed files with 56 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
Documentation/platforms/avr/at90usb/boards/micropendous3/README.txt
View File

@@ -526,6 +526,11 @@ Common Configuration Notes
CONFIG_WINDOWS_CYGWIN=y
CONFIG_AVR_BUILDROOT_TOOLCHAIN=y
4. Build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS by default.
This is because the linker script was not checked to determine
if it properly prevents removal of sections which the linker considers
unreferenced but which must be present in the binary.
Configuration Sub-Directories
-----------------------------

5
Documentation/platforms/avr/at90usb/boards/teensy-2.0/README.txt
View File

@@ -535,6 +535,11 @@ Common Configuration Notes
CONFIG_WINDOWS_CYGWIN=y
CONFIG_AVR_BUILDROOT_TOOLCHAIN=y
4. Build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS by default.
This is because the linker script was not checked to determine
if it properly prevents removal of sections which the linker considers
unreferenced but which must be present in the binary.
Configuration Sub-Directories
-----------------------------

5
Documentation/platforms/avr/atmega/boards/amber/README.txt
View File

@@ -506,6 +506,11 @@ Common Configuration Notes
CONFIG_WINDOWS_CYGWIN=y
CONFIG_AVR_BUILDROOT_TOOLCHAIN=y
4. Build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS by default.
This is because the linker script was not checked to determine
if it properly prevents removal of sections which the linker considers
unreferenced but which must be present in the binary.
Configuration Sub-Directories
-----------------------------

5
Documentation/platforms/avr/atmega/boards/arduino-mega2560/README.txt
View File

@@ -69,6 +69,11 @@ Configurations
CONFIG_WINDOWS_CYGWIN=y
CONFIG_AVR_BUILDROOT_TOOLCHAIN=y
4. Build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS by default.
This is because the linker script was not checked to determine
if it properly prevents removal of sections which the linker considers
unreferenced but which must be present in the binary.
Configuration Sub-Directories
-----------------------------
hello:

9
Documentation/platforms/avr/atmega/boards/mega1284p-xplained/index.rst
View File

@@ -46,6 +46,15 @@ nsh
Basic NuttShell configuration (console enabled in USART0, pins PD0 (RXD0) and PD1 (TXD0), at 115200 bps).
Compile
=======
Note that build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS
by default. This is because the linker script was not checked
to determine if it properly prevents removal of sections which
the linker considers unreferenced but which must be present
in the binary.
Flash & Debug
=============

5
Documentation/platforms/avr/atmega/boards/moteino-mega/README.txt
View File

@@ -254,6 +254,11 @@ Common Configuration Notes
b. Execute 'make menuconfig' in nuttx/ in order to start the
reconfiguration process.
4. Build with GCC disables CONFIG_DEBUG_OPT_UNUSED_SECTIONS by default.
This is because the linker script was not checked to determine
if it properly prevents removal of sections which the linker considers
unreferenced but which must be present in the binary.
Configuration Sub-Directories
-----------------------------

31
arch/avr/src/avr/Kconfig
View File

@@ -37,10 +37,21 @@ config AVR_ATMEL_AVR_TOOLCHAIN
config AVR_LINUXGCC_TOOLCHAIN
bool "Linux GCC"
depends on HOST_LINUX
select ARCH_TOOLCHAIN_GCC
---help---
For Linux, there are widely available avr-gcc packages. On
Ubuntu, use: sudo apt-get install gcc-avr gdb-avr avr-libc
Note that unlike other toolchains, this one is marked
with ARCH_TOOLCHAIN_GCC which in turn enables other GCC-
and GNU-specific optimizations. One of them is removal
of unused code sections by the linker.
Linker script for the board must take this into account
and flag unreferenced sections that need to be present
in the compiled binary with a KEEP statement. Most notably,
this applies to .vectors section.
config AVR_CROSSPACK_TOOLCHAIN
bool "CrossPack-AVR"
depends on HOST_MACOS
@@ -57,26 +68,6 @@ config AVR_BUILDROOT_TOOLCHAIN
endchoice # Toolchain
config AVR_LINUXGCC_TOOLCHAIN_IS_GCC
bool "Mark the toolchain as a GCC toolchain"
default n
depends on AVR_LINUXGCC_TOOLCHAIN
select ARCH_TOOLCHAIN_GCC
---help---
This option marks the toolchain as a GCC toolchain. Enabling
this will in turn enable other configuration option. Among
them, there is DEBUG_OPT_UNUSED_SECTIONS which will instruct
the compiler and linker to remove unused sections from the final
binary, saving flash space.
There is, however, a catch to this. Linker script for the board
in use must mark unreferenced sections as "KEEP". Most notably,
this applies to .vectors section which is not referenced anywhere
but must be present. If not marked to be kept, the resulting
binary will be faulty.
Consult linker script of your board before enabling this option.
config AVR_HAS_MEMX_PTR
bool "Enable in-flash static const strings"
depends on AVR_ATMEL_AVR_TOOLCHAIN || AVR_LINUXGCC_TOOLCHAIN

1
boards/avr/at90usb/micropendous3/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="micropendous3"

1
boards/avr/at90usb/teensy-2.0/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="teensy-2.0"

1
boards/avr/at90usb/teensy-2.0/configs/nsh/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
# CONFIG_DISABLE_ENVIRON is not set
# CONFIG_NSH_DISABLEBG is not set
# CONFIG_NSH_DISABLE_IFCONFIG is not set

1
boards/avr/at90usb/teensy-2.0/configs/usbmsc/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
# CONFIG_SPI_EXCHANGE is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y

1
boards/avr/atmega/amber/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="amber"

1
boards/avr/atmega/arduino-mega2560/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="arduino-mega2560"

1
boards/avr/atmega/arduino-mega2560/configs/nsh/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="arduino-mega2560"

1
boards/avr/atmega/mega1284p-xplained/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="mega1284p-xplained"

1
boards/avr/atmega/mega1284p-xplained/configs/nsh/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
# CONFIG_DISABLE_ENVIRON is not set
# CONFIG_NSH_DISABLEBG is not set
# CONFIG_NSH_DISABLE_IFCONFIG is not set

1
boards/avr/atmega/moteino-mega/configs/hello/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="moteino-mega"

1
boards/avr/atmega/moteino-mega/configs/nsh/defconfig
View File

@@ -5,6 +5,7 @@
# You can then do "make savedefconfig" to generate a new defconfig file that includes your
# modifications.
#
# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
# CONFIG_DISABLE_ENVIRON is not set
# CONFIG_NSH_DISABLEBG is not set
# CONFIG_NSH_DISABLE_IFCONFIG is not set