* [PATCH] [EXPERIMENTAL, v2] enable thin archives and --gc-sections on ARM
@ 2017-03-15 16:50 Arnd Bergmann
2017-03-17 9:17 ` Alan Modra
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2017-03-15 16:50 UTC (permalink / raw)
Cc: Arnd Bergmann, Nicolas Pitre, Nicholas Piggin, Alan Modra,
Russell King, linux-arm-kernel, linux-kernel
I'm still build testing with an experimental change to enable
thin architeves and --gc-sections on ARM, which should bring
multiple benefits
- improve build times
- allow 'allyesconfig' to succeed without exceeding the
section size when linking drivers/built-in.o
- reduce the kernel image size
However, I have now run into a build error binutils commit
f02cb05 ("Always descend into output section statements in
lang_do_assignments") in binutils-2.28 and later:
no __ex_table in file: vmlinux
Any idea what's going wrong here?
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Alan Modra <amodra@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/arm/Kconfig | 2 ++
arch/arm/kernel/Makefile | 3 +++
arch/arm/kernel/vmlinux-xip.lds.S | 32 +++++++++++++++++++++-----------
arch/arm/kernel/vmlinux.lds.S | 22 ++++++++++++++++------
4 files changed, 42 insertions(+), 17 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 27e738b82e45..333a1f685abb 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -89,6 +89,7 @@ config ARM
select HAVE_UID16
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select IRQ_FORCED_THREADING
+ select LD_DEAD_CODE_DATA_ELIMINATION
select MODULES_USE_ELF_REL
select NO_BOOTMEM
select OF_EARLY_FLATTREE if OF
@@ -98,6 +99,7 @@ config ARM
select PERF_USE_VMALLOC
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
+ select THIN_ARCHIVES
# Above selects are sorted alphabetically; please add new ones
# according to that. Thanks.
help
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index d1b06cd79b23..469b78f5f529 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -13,6 +13,9 @@ endif
CFLAGS_REMOVE_return_address.o = -pg
+ccflags-y += -fno-function-sections -fno-data-sections
+subdir-ccflags-y += -fno-function-sections -fno-data-sections
+
# Object file lists.
obj-y := elf.o entry-common.o irq.o opcodes.o \
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 2e5b5f0dbadf..bf900f5421a1 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -18,17 +18,17 @@
#define PROC_INFO \
. = ALIGN(4); \
VMLINUX_SYMBOL(__proc_info_begin) = .; \
- *(.proc.info.init) \
+ KEEP(*(.proc.info.init)) \
VMLINUX_SYMBOL(__proc_info_end) = .;
#define IDMAP_TEXT \
ALIGN_FUNCTION(); \
VMLINUX_SYMBOL(__idmap_text_start) = .; \
- *(.idmap.text) \
+ KEEP(*(.idmap.text)) \
VMLINUX_SYMBOL(__idmap_text_end) = .; \
. = ALIGN(PAGE_SIZE); \
VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \
- *(.hyp.idmap.text) \
+ KEEP(*(.hyp.idmap.text)) \
VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
#ifdef CONFIG_HOTPLUG_CPU
@@ -48,6 +48,16 @@
#define ARM_EXIT_DISCARD(x) x
#endif
+#undef TEXT_TEXT
+#define TEXT_TEXT \
+ ALIGN_FUNCTION(); \
+ *(.text.hot .text.hot.*) \
+ *(.text.unlikely .text.unlikely.*) \
+ *(.text .text.*) \
+ *(.ref.text) \
+ MEM_KEEP(init.text) \
+ MEM_KEEP(exit.text) \
+
OUTPUT_ARCH(arm)
ENTRY(stext)
@@ -121,7 +131,7 @@ SECTIONS
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
__start___ex_table = .;
#ifdef CONFIG_MMU
- *(__ex_table)
+ KEEP(*(__ex_table))
#endif
__stop___ex_table = .;
}
@@ -133,12 +143,12 @@ SECTIONS
. = ALIGN(8);
.ARM.unwind_idx : {
__start_unwind_idx = .;
- *(.ARM.exidx*)
+ KEEP(*(.ARM.exidx*))
__stop_unwind_idx = .;
}
.ARM.unwind_tab : {
__start_unwind_tab = .;
- *(.ARM.extab*)
+ KEEP(*(.ARM.extab*))
__stop_unwind_tab = .;
}
#endif
@@ -153,7 +163,7 @@ SECTIONS
*/
__vectors_start = .;
.vectors 0xffff0000 : AT(__vectors_start) {
- *(.vectors)
+ KEEP(*(.vectors))
}
. = __vectors_start + SIZEOF(.vectors);
__vectors_end = .;
@@ -176,24 +186,24 @@ SECTIONS
}
.init.arch.info : {
__arch_info_begin = .;
- *(.arch.info.init)
+ KEEP(*(.arch.info.init))
__arch_info_end = .;
}
.init.tagtable : {
__tagtable_begin = .;
- *(.taglist.init)
+ KEEP(*(.taglist.init))
__tagtable_end = .;
}
#ifdef CONFIG_SMP_ON_UP
.init.smpalt : {
__smpalt_begin = .;
- *(.alt.smp.init)
+ KEEP(*(.alt.smp.init))
__smpalt_end = .;
}
#endif
.init.pv_table : {
__pv_table_begin = .;
- *(.pv_table)
+ KEEP(*(.pv_table))
__pv_table_end = .;
}
.init.data : {
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 30f04ce52dde..5f2c8c90beac 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -17,7 +17,7 @@
#define PROC_INFO \
. = ALIGN(4); \
VMLINUX_SYMBOL(__proc_info_begin) = .; \
- *(.proc.info.init) \
+ KEEP(*(.proc.info.init)) \
VMLINUX_SYMBOL(__proc_info_end) = .;
#define HYPERVISOR_TEXT \
@@ -35,6 +35,16 @@
*(.hyp.idmap.text) \
VMLINUX_SYMBOL(__hyp_idmap_text_end) = .;
+#undef TEXT_TEXT
+#define TEXT_TEXT \
+ ALIGN_FUNCTION(); \
+ *(.text.hot .text.hot.*) \
+ *(.text.unlikely .text.unlikely.*) \
+ *(.text .text.*) \
+ *(.ref.text) \
+ MEM_KEEP(init.text) \
+ MEM_KEEP(exit.text) \
+
#ifdef CONFIG_HOTPLUG_CPU
#define ARM_CPU_DISCARD(x)
#define ARM_CPU_KEEP(x) x
@@ -170,7 +180,7 @@ SECTIONS
*/
__vectors_start = .;
.vectors 0xffff0000 : AT(__vectors_start) {
- *(.vectors)
+ KEEP(*(.vectors))
}
. = __vectors_start + SIZEOF(.vectors);
__vectors_end = .;
@@ -193,24 +203,24 @@ SECTIONS
}
.init.arch.info : {
__arch_info_begin = .;
- *(.arch.info.init)
+ KEEP(*(.arch.info.init))
__arch_info_end = .;
}
.init.tagtable : {
__tagtable_begin = .;
- *(.taglist.init)
+ KEEP(*(.taglist.init))
__tagtable_end = .;
}
#ifdef CONFIG_SMP_ON_UP
.init.smpalt : {
__smpalt_begin = .;
- *(.alt.smp.init)
+ KEEP(*(.alt.smp.init))
__smpalt_end = .;
}
#endif
.init.pv_table : {
__pv_table_begin = .;
- *(.pv_table)
+ KEEP(*(.pv_table))
__pv_table_end = .;
}
.init.data : {
--
2.9.0
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] [EXPERIMENTAL, v2] enable thin archives and --gc-sections on ARM
2017-03-15 16:50 [PATCH] [EXPERIMENTAL, v2] enable thin archives and --gc-sections on ARM Arnd Bergmann
@ 2017-03-17 9:17 ` Alan Modra
0 siblings, 0 replies; 2+ messages in thread
From: Alan Modra @ 2017-03-17 9:17 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Nicolas Pitre, Nicholas Piggin, Russell King, linux-arm-kernel,
linux-kernel
On Wed, Mar 15, 2017 at 05:50:00PM +0100, Arnd Bergmann wrote:
> I'm still build testing with an experimental change to enable
> thin architeves and --gc-sections on ARM, which should bring
> multiple benefits
>
> - improve build times
> - allow 'allyesconfig' to succeed without exceeding the
> section size when linking drivers/built-in.o
> - reduce the kernel image size
>
> However, I have now run into a build error binutils commit
> f02cb05 ("Always descend into output section statements in
> lang_do_assignments") in binutils-2.28 and later:
>
> no __ex_table in file: vmlinux
>
> Any idea what's going wrong here?
I presume you checked that section really had disappeared?
> __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
> __start___ex_table = .;
> #ifdef CONFIG_MMU
> - *(__ex_table)
> + KEEP(*(__ex_table))
> #endif
> __stop___ex_table = .;
> }
I think that if CONFIG_MMU is not defined, then ld will remove the
empty section.
--
Alan Modra
Australia Development Lab, IBM
^ permalink raw reply [flat|nested] 2+ messages in thread
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