On Wed, Nov 14, 2018 at 09:20:23PM +1100, Michael Ellerman wrote: > Joel Stanley <joel@xxxxxxxxx> writes: > > Hello Alan, > > > > On Tue, 12 Jun 2018 at 07:44, Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote: > > > >> Building Linus' tree, today's linux-next build (powerpc ppc64_defconfig) > >> produced these warning: > >> > >> ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'. > >> ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'. > >> ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'. > >> > >> This may just be because I have started building using the native Debian > >> gcc for the powerpc builds ... > > > > Do you know why we started creating these? > > It's controlled by the ld option --hash-style, which AFAICS still > defaults to sysv (generating .hash). > > But it seems gcc can be configured to have a different default, and at > least my native ppc64le toolchains are passing gnu, eg: > > /usr/lib/gcc/powerpc64le-linux-gnu/6/collect2 -plugin > /usr/lib/gcc/powerpc64le-linux-gnu/6/liblto_plugin.so > -plugin-opt=/usr/lib/gcc/powerpc64le-linux-gnu/6/lto-wrapper > -plugin-opt=-fresolution=/tmp/ccw1U2fF.res > -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s > -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc > -plugin-opt=-pass-through=-lgcc_s --sysroot=/ --build-id --eh-frame-hdr > -V -shared -m elf64lppc > --hash-style=gnu > ^^^^^^^^^^^^^^^^ > > So that's presumably why we're seeing it, some GCCs are configured to > use it. > > > If it's intentional, should we be putting including them in the same > > way as .hash sections? > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/vmlinux.lds.S#n282 > > > > .hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) } > > That would presumably work. > > My question though is do we even need it? > > >From what I can see for it to be useful you need the section as well as > an entry in the dynamic section pointing at it, and we don't have a > dynamic section at all: > > $ readelf -S vmlinux | grep gnu.hash > [ 4] .gnu.hash GNU_HASH c000000000dbbdb0 00dcbdb0 > $ readelf -d vmlinux > > There is no dynamic section in this file. > > Compare to the vdso: > > $ readelf -d arch/powerpc/kernel/vdso64/vdso64.so > > Dynamic section at offset 0x868 contains 12 entries: > Tag Type Name/Value > 0x000000000000000e (SONAME) Library soname: [linux-vdso64.so.1] > 0x0000000000000004 (HASH) 0x120 > 0x000000006ffffef5 (GNU_HASH) 0x170 > 0x0000000000000005 (STRTAB) 0x320 > 0x0000000000000006 (SYMTAB) 0x1d0 > 0x000000000000000a (STRSZ) 269 (bytes) > 0x000000000000000b (SYMENT) 24 (bytes) > 0x0000000070000003 (PPC64_OPT) 0x0 > 0x000000006ffffffc (VERDEF) 0x450 > 0x000000006ffffffd (VERDEFNUM) 2 > 0x000000006ffffff0 (VERSYM) 0x42e > 0x0000000000000000 (NULL) 0x0 > > > So can't we just discard .gnu.hash? And in fact do we need .hash either? > > Actually arm64 discards the latter, and parisc discards both. > > Would still be good to hear from Alan or someone else who knows anything > about toolchain stuff, ie. not me :) .gnu.hash, like .hash, is used by glibc ld.so for dynamic symbol lookup. I imagine you don't need either section in a kernel, so discarding both sounds reasonable. Likely you could discard .interp and .dynstr too, and .dynsym when !CONFIG_PPC32. -- Alan Modra Australia Development Lab, IBM
