Messages in this thread |  | | | Date | Tue, 10 Mar 2009 12:24:10 +0100 | | From | Sam Ravnborg <> | | Subject | Re: Absolute symbols in vmlinux_64.lds.S |
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On Mon, Mar 09, 2009 at 10:57:19PM -0700, Yinghai Lu wrote: > 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....
So you say that we do hit this issue here - right. But the better way to do it is to include the assignment inside the {} block, thus we are not dependent on an ALIGN() that logically belongs to .data_nosave. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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