I think the objtool works on individual object files (or vmlinux.o). The -Wl,--gc-sections flag, on the other hand, is a linker flag that acts on the final link -- it's applied after objtool invocations. Therefore, even with -Wl,--gc-sections, we'll still encounter those spurious warnings from objtool. -Rong On Mon, Oct 28, 2024 at 5:19 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote: > > On 10/28/24 17:16, Kees Cook wrote: > > On Fri, Oct 25, 2024 at 10:14:04PM -0700, Rong Xu wrote: > >> In the presence of both weak and strong function definitions, the > >> linker drops the weak symbol in favor of a strong symbol, but > >> leaves the code in place. Code in ignore_unreachable_insn() has > >> some heuristics to suppress the warning, but it does not work when > >> -ffunction-sections is enabled. > >> > >> Suppose function foo has both strong and weak definitions. > >> Case 1: The strong definition has an annotated section name, > >> like .init.text. Only the weak definition will be placed into > >> .text.foo. But since the section has no symbols, there will be no > >> "hole" in the section. > >> > >> Case 2: Both sections are without an annotated section name. > >> Both will be placed into .text.foo section, but there will be only one > >> symbol (the strong one). If the weak code is before the strong code, > >> there is no "hole" as it fails to find the right-most symbol before > >> the offset. > >> > >> The fix is to use the first node to compute the hole if hole.sym > >> is empty. If there is no symbol in the section, the first node > >> will be NULL, in which case, -1 is returned to skip the whole > >> section. > >> > >> Co-developed-by: Han Shen <shenhan@xxxxxxxxxx> > >> Signed-off-by: Han Shen <shenhan@xxxxxxxxxx> > > > > This seems logically correct to me, but I'd love to see review from Josh > > and/or Peter Z on this change too. > > > > Reviewed-by: Kees Cook <kees@xxxxxxxxxx> > > > > Does this happen even with -Wl,--gc-sections? > > -hpa >
