On Wed, Jun 24, 2020 at 10:26:20AM -0700, Fangrui Song wrote: > > On 2020-06-24, Arvind Sankar wrote: > >On Wed, Jun 24, 2020 at 09:16:43AM -0700, Fangrui Song wrote: > >> > >> On 2020-06-24, Arvind Sankar wrote: > >> >On Tue, Jun 23, 2020 at 06:49:33PM -0700, Kees Cook wrote: > >> >> When linking vmlinux with LLD, the synthetic sections .symtab, .strtab, > >> >> and .shstrtab are listed as orphaned. Add them to the STABS_DEBUG section > >> >> so there will be no warnings when --orphan-handling=warn is used more > >> >> widely. (They are added above comment as it is the more common > >> > > >> >Nit 1: is "after .comment" better than "above comment"? It's above in the > >> >sense of higher file offset, but it's below in readelf output. > >> > >> I mean this order:) > >> > >> .comment > >> .symtab > >> .shstrtab > >> .strtab > >> > >> This is the case in the absence of a linker script if at least one object file has .comment (mostly for GCC/clang version information) or the linker is LLD which adds a .comment > >> > >> >Nit 2: These aren't actually debugging sections, no? Is it better to add > >> >a new macro for it, and is there any plan to stop LLD from warning about > >> >them? > >> > >> https://reviews.llvm.org/D75149 "[ELF] --orphan-handling=: don't warn/error for unused synthesized sections" > >> described that .symtab .shstrtab .strtab are different in GNU ld. > >> Since many other GNU ld synthesized sections (.rela.dyn .plt ...) can be renamed or dropped > >> via output section descriptions, I don't understand why the 3 sections > >> can't be customized. > > > >So IIUC, lld will now warn about .rela.dyn etc only if they're non-empty? > > HEAD and future 11.0.0 will not warn about unused synthesized sections > like .rela.dyn > > For most synthesized sections, empty = unused. > > >> > >> I created a feature request: https://sourceware.org/bugzilla/show_bug.cgi?id=26168 > >> (If this is supported, it is a consistent behavior to warn for orphan > >> .symtab/.strtab/.shstrtab > >> > >> There may be 50% chance that the maintainer decides that "LLD diverges" > >> I would disagree: there is no fundamental problems with .symtab/.strtab/.shstrtab which make them special in output section descriptions or orphan handling.) > >> > > > >.shstrtab is a little special in that it can't be discarded if the ELF > >file contains any sections at all. But yeah, there's no reason they > >can't be renamed or placed in a custom location in the file. > > https://sourceware.org/pipermail/binutils/2020-March/000179.html > proposes -z nosectionheader. With this option, I believe .shstrtab is > not needed. /DISCARD/ : { *(.shstrtab) } should achieve a similar effect. oh wow.
