Date: Thu, 7 Sep 2023 08:48:28 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: aarch64 sigsetjmp relocation truncation bug, maybe On Thu, Sep 07, 2023 at 05:08:13AM +0200, Markus Wichmann wrote: > Am Wed, Sep 06, 2023 at 08:46:32PM -0400 schrieb Peter Williams: > > If I'm understanding correctly, the complaint is that a branch in > > sigsetjmp that invokes setjmp is too far away from the definition of > > setjmp. My very handwavey idea is that maybe for some reason my program > > is causing the linker to want to locate setjmp() and sigsetjmp() really > > far away from each other. If that's right, perhaps it would be possible > > to modify the assembler code to be able to handle such a situation? > > I'm guessing the same. Pretty much all architectures have shorter > conditional than unconditional branches. That is why branches to other > files (technically to other sections) should always be unconditional. I > am attaching a simple patch that should help with the situation. > > Ciao, > Markus > From dd227e22a5337d54e1cb0838410bca6672c76c43 Mon Sep 17 00:00:00 2001 > From: Markus Wichmann <nullplan@....net> > Date: Thu, 7 Sep 2023 05:01:23 +0200 > Subject: [PATCH] Make branch to external symbol unconditional. > > Conditional branches have a shorter branch length than unconditional > ones, and almost all ABIs require unconditional branches to external > symbols. Otherwise linkers may create broken binaries. > --- > src/signal/aarch64/sigsetjmp.s | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/src/signal/aarch64/sigsetjmp.s b/src/signal/aarch64/sigsetjmp..s > index 75910c43..9a28e395 100644 > --- a/src/signal/aarch64/sigsetjmp.s > +++ b/src/signal/aarch64/sigsetjmp.s > @@ -4,7 +4,7 @@ > .type __sigsetjmp,%function > sigsetjmp: > __sigsetjmp: > - cbz x1,setjmp > + cbz x1,1f > > str x30,[x0,#176] > str x19,[x0,#176+8+8] > @@ -19,3 +19,5 @@ __sigsetjmp: > > .hidden __sigsetjmp_tail > b __sigsetjmp_tail > + > +1: b setjmp > -- > 2.39.2 Are you sure this is the actual problem? I think it's that the aarch64 (and several other archs) version of sigsetjmp is wrongly using the public setjmp symbol whose definition is possibly provided by a PLT thunk in the main program, rather than either setjmp@PLT (which would necessarily be the right local call point to use) or the hidden ___setjmp symbol that exists for this purpose (which i386, for example, uses). Rich
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