On Sun, May 24, 2020 at 03:13:26PM -0700, Fangrui Song wrote: > On 2020-05-24, Arvind Sankar wrote: > >gcc puts the main function into .text.startup when compiled with -Os (or > >-O2). This results in arch/x86/boot/main.c having a .text.startup > >section which is currently not included explicitly in the linker script > >setup.ld in the same directory. > > > >The BFD linker places this orphan section immediately after .text, so > >this still works. However, LLD git, since [1], is choosing to place it > >immediately after the .bstext section instead (this is the first code > >section). This plays havoc with the section layout that setup.elf > >requires to create the setup header, for eg on 64-bit: > > > > LD arch/x86/boot/setup.elf > > ld.lld: error: section .text.startup file range overlaps with .header > > >>> .text.startup range is [0x200040, 0x2001FE] > > >>> .header range is [0x2001EF, 0x20026B] > > > > ld.lld: error: section .header file range overlaps with .bsdata > > >>> .header range is [0x2001EF, 0x20026B] > > >>> .bsdata range is [0x2001FF, 0x200398] > > > > ld.lld: error: section .bsdata file range overlaps with .entrytext > > >>> .bsdata range is [0x2001FF, 0x200398] > > >>> .entrytext range is [0x20026C, 0x2002D3] > > > > ld.lld: error: section .text.startup virtual address range overlaps > > with .header > > >>> .text.startup range is [0x40, 0x1FE] > > >>> .header range is [0x1EF, 0x26B] > > > > ld.lld: error: section .header virtual address range overlaps with > > .bsdata > > >>> .header range is [0x1EF, 0x26B] > > >>> .bsdata range is [0x1FF, 0x398] > > > > ld.lld: error: section .bsdata virtual address range overlaps with > > .entrytext > > >>> .bsdata range is [0x1FF, 0x398] > > >>> .entrytext range is [0x26C, 0x2D3] > > > > ld.lld: error: section .text.startup load address range overlaps with > > .header > > >>> .text.startup range is [0x40, 0x1FE] > > >>> .header range is [0x1EF, 0x26B] > > > > ld.lld: error: section .header load address range overlaps with > > .bsdata > > >>> .header range is [0x1EF, 0x26B] > > >>> .bsdata range is [0x1FF, 0x398] > > > > ld.lld: error: section .bsdata load address range overlaps with > > .entrytext > > >>> .bsdata range is [0x1FF, 0x398] > > >>> .entrytext range is [0x26C, 0x2D3] > > > >Explicitly pull .text.startup into the .text output section to avoid > >this. > > > >[1] https://reviews.llvm.org/D75225 > > > >Signed-off-by: Arvind Sankar <[email protected]> > >Reviewed-by: Fangrui Song <[email protected]> > >--- > > arch/x86/boot/setup.ld | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld > >index 24c95522f231..ed60abcdb089 100644 > >--- a/arch/x86/boot/setup.ld > >+++ b/arch/x86/boot/setup.ld > >@@ -20,7 +20,7 @@ SECTIONS > > .initdata : { *(.initdata) } > > __end_init = .; > > > >- .text : { *(.text) } > >+ .text : { *(.text.startup) *(.text) } > > .text32 : { *(.text32) } > > > > . = ALIGN(16); > >-- > >2.26.2 > > Should .text.startup* be used instead? If -ffunction-sections is used, > > // a.c > int main() {} > > gcc -O2 a.c # .text.startup > gcc -Os a.c # .text.startup > > gcc -O2 -ffunction-sections a.c # .text.startup.main > gcc -Os -ffunction-sections a.c # .text.startup.main
It's probably unlikely we'll use function-sections on the setup code, but *(.text.*) might be more future-proof, since gcc/clang might grow the ability to stick code into .text.hot or .text.unlikely etc automatically. > > ----- > > In case anyone wants to CC a GCC dev for the citation that > main compiles to `.text.startup` in -Os or -O2 mode, I have a small request > that `.text.startup.` probably makes more sense. See > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95095 > > I made an llvm change recently https://reviews.llvm.org/D79600
