linux-kernel - [PATCH] powerpc/vdso32: mark __kernel_datapage_offset as STV

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Date:   Tue, 4 Feb 2020 16:50:54 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Fangrui Song <maskray@...gle.com>
Subject: [PATCH] powerpc/vdso32: mark __kernel_datapage_offset as
 STV_PROTECTED

A PC-relative relocation (R_PPC_REL16_LO in this case) referencing a
preemptible symbol in a -shared link is not allowed.  GNU ld's powerpc
port is permissive and allows it [1], but lld will report an error after
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id=ec0895f08f99515194e9fcfe1338becf6f759d38

Make the symbol protected so that it is non-preemptible but still
exported.

[1]: https://sourceware.org/bugzilla/show_bug.cgi?id=25500

Link: https://github.com/ClangBuiltLinux/linux/issues/851
Signed-off-by: Fangrui Song <maskray@...gle.com>
---
 arch/powerpc/kernel/vdso32/datapage.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vdso32/datapage.S b/arch/powerpc/kernel/vdso32/datapage.S
index 217bb630f8f9..2831a8676365 100644
--- a/arch/powerpc/kernel/vdso32/datapage.S
+++ b/arch/powerpc/kernel/vdso32/datapage.S
@@ -13,7 +13,8 @@
 #include <asm/vdso_datapage.h>
 
 	.text
-	.global	__kernel_datapage_offset;
+	.global	__kernel_datapage_offset
+	.protected	__kernel_datapage_offset
 __kernel_datapage_offset:
 	.long	0
 
-- 
2.25.0.341.g760bfbb309-goog