Messages in this thread | | | Date | Mon, 9 Mar 2009 22:57:19 -0700 | Subject | Re: Absolute symbols in vmlinux_64.lds.S | From | Yinghai Lu <> |
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On Mon, Mar 9, 2009 at 10:37 PM, Sam Ravnborg <sam@ravnborg.org> wrote: > On Mon, Mar 09, 2009 at 06:23:55PM -0700, Yinghai Lu wrote: >> Jeremy Fitzhardinge wrote: >> > Why does vmlinux_64.lds.S use absolute symbols for things like >> > __bss_start/stop: >> > >> > __bss_start = .; /* BSS */ >> > .bss : AT(ADDR(.bss) - LOAD_OFFSET) { >> > *(.bss.page_aligned) >> > *(.bss) >> > } >> > __bss_stop = .; >> > >> > >> > vmlinux_32.lds.S puts __bss_start/stop into the .bss section itself. Is >> > there some particular reason they need to be absolute symbols >> > (relocation?). >> > >> >> they are the same. > > Thats depends on the value of '.' where you assign __bss_start. > We have had several bugs where the symbol assinged outside the > section was less than expected because the linker aling the > start of the section equal to the lrgest alignment requirement > of a member in the section. > > So in this case if '.' equals to 0xabcd and the lagest > alignment requirement inside the block is 0x1000 and we have > __bss_start1 = .; > .bss : { > __bss_start2 = .; > *(.bss.page_aligned) > } > > Then you would see that: > __bss_start1 equals 0xabcd > __bss_start2 equals 0xb000
good to know...
anyway, more lines
. = ALIGN(PAGE_SIZE); __nosave_begin = .; .data_nosave : AT(ADDR(.data_nosave) - LOAD_OFFSET) { *(.data.nosave) } :data.init2 /* use another section data.init2, see PERCPU_VADDR() above */ . = ALIGN(PAGE_SIZE); __nosave_end = .;
__bss_start = .; /* BSS */ .bss : AT(ADDR(.bss) - LOAD_OFFSET) { *(.bss.page_aligned) *(.bss) } __bss_stop = .;
_end = . ;
there are extra ALIGN(PAGE_SIZE) between them....
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