Date: Mon, 21 Oct 2019 22:59:42 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH] remove remaining traces of __tls_get_new On Mon, Oct 21, 2019 at 05:50:30PM -0700, Fangrui Song wrote: > On 2019-09-29, Rich Felker wrote: > >On Sun, Sep 29, 2019 at 03:05:27PM +0200, Szabolcs Nagy wrote: > >>reported on irc by malc_ > > > >>>From 4a7090ab76d81b59f57a83bce9d22582e35a8b2b Mon Sep 17 00:00:00 2001 > >>From: Szabolcs Nagy <nsz@...t70.net> > >>Date: Sun, 29 Sep 2019 12:25:39 +0000 > >>Subject: [PATCH] remove remaining traces of __tls_get_new > >> > >>Some declarations of __tls_get_new were left in the code, even > >>though the definition got removed in > >> > >> commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 > >> install dynamic tls synchronously at dlopen, streamline access > >> > >>this can make the build fail with > >> > >> ld: lib/libc.so: hidden symbol `__tls_get_new' isn't defined > >> > >>when libc.so is linked without --gc-sections, because a .hidden > >>declaration in asm code creates a reference even if the symbol > >>is not actually used. > > > >This is definitely a tooling bug. There is no reference to the symbol, > >only declarations of it. I think it's a good idea to cleanup the > >spurious mentions of it anyway, though. > > I think it is hard to simply state that this is a tooling bug. > For the visibility attribute of a symbol, it may still be emitted into > the symbol table even if it is unused. For example: > > ..protected foo => STV_PROTECTED foo > ..hidden foo => STV_HIDDEN foo > > A relocation referencing a symbol may be dropped due to --gc-sections. > Shall we consider the symbol unused if all relocations to it are > dropped? I don't think --gc-sections is relevant except that it happened to make the problem go away. This isn't about ld spuriously thinking there's a reference to a symbol after --gc-sections dropped the sections containing relocations referencing it. Rather, it looks like a bug in --no-undefined, which as documented should only produce an error when there's a *reference* (i.e. an outstanding relocation using) the undefined symbol, instead erroring out just because an undefined symbol appears in the linker's working symbol table for the purpose of tracking its declared visibility. Rich
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