On Thu, 11 Aug 2016, Arnd Bergmann wrote:
> This goes on top of Nick's latest version of "[PATCH 0/6 v2] kbuild changes,
> thin archives, --gc-sections" and enables both features on ARM.
>
[...]
>
> - I mark a ton of sections as KEEP() in vmlinux.lds.S. Some of
> them might not actually be needed, and I have not spent much
> time checking what they actually are. However, I did build
> a few hundred randconfigs without new issues.
>
> index 7396a5f00c5f..61b9b8784036 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)) \
OK.
> VMLINUX_SYMBOL(__proc_info_end) = .;
>
> #define HYPERVISOR_TEXT \
> @@ -104,7 +104,7 @@ SECTIONS
> _stext = .; /* Text and read-only data */
> IDMAP_TEXT
> __exception_text_start = .;
> - *(.exception.text)
> + KEEP(*(.exception.text))
No need here. The code there has to be referenced from somewhere. If not
it should not be kept.
> __exception_text_end = .;
> IRQENTRY_TEXT
> SOFTIRQENTRY_TEXT
> @@ -169,14 +169,14 @@ SECTIONS
> */
> __vectors_start = .;
> .vectors 0xffff0000 : AT(__vectors_start) {
> - *(.vectors)
> + KEEP(*(.vectors))
OK.
> }
> . = __vectors_start + SIZEOF(.vectors);
> __vectors_end = .;
>
> __stubs_start = .;
> .stubs ADDR(.vectors) + 0x1000 : AT(__stubs_start) {
> - *(.stubs)
> + KEEP(*(.stubs))
This is referenced from .vectors entries and therefore the KEEP() is not
needed. There is nothing to be saved either ways though.
> }
> . = __stubs_start + SIZEOF(.stubs);
> __stubs_end = .;
> @@ -192,24 +192,24 @@ SECTIONS
> }
> .init.arch.info : {
> __arch_info_begin = .;
> - *(.arch.info.init)
> + KEEP(*(.arch.info.init))
OK.
> __arch_info_end = .;
> }
> .init.tagtable : {
> __tagtable_begin = .;
> - *(.taglist.init)
> + KEEP(*(.taglist.init))
OK.
> __tagtable_end = .;
> }
> #ifdef CONFIG_SMP_ON_UP
> .init.smpalt : {
> __smpalt_begin = .;
> - *(.alt.smp.init)
> + KEEP(*(.alt.smp.init))
Yes unfortunately this needs a KEEP() right now as there is no explicit
references to those entries. But by doing so you force a reference from
those entries to all functions they annotate, preventing those functions
from being discarded if there isn't any reference to that code
otherwise. That's a case that falls into the "missing forward reference"
category in my slides.
> __smpalt_end = .;
> }
> #endif
> .init.pv_table : {
> __pv_table_begin = .;
> - *(.pv_table)
> + KEEP(*(.pv_table))
Ditto here.
Nicolas
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