Re: [musl] aarch64 sigsetjmp relocation truncation bug, maybe

[Markus Wichmann <nullplan@gmx.net>]

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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

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From dd227e22a5337d54e1cb0838410bca6672c76c43 Mon Sep 17 00:00:00 2001
From: Markus Wichmann <nullplan@gmx.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