linux-kernel - [PATCH] x86/vdso: Conditionally export __vdso_sgx_enter

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Date:   Tue,  8 Nov 2022 17:03:07 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] x86/vdso: Conditionally export __vdso_sgx_enter_enclave

Recently, ld.lld moved from '--undefined-version' to
'--no-undefined-version' as the default, which breaks building the vDSO
when CONFIG_X86_SGX is not set:

  ld.lld: error: version script assignment of 'LINUX_2.6' to symbol '__vdso_sgx_enter_enclave' failed: symbol not defined

__vdso_sgx_enter_enclave is only included in the vDSO when
CONFIG_X86_SGX is set. Only export it if it will be present in the final
object, which clears up the error.

Link: https://github.com/ClangBuiltLinux/linux/issues/1756
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

It would be nice if this could be picked up for an -rc release but I
won't argue otherwise.

Alternatively, we could add '--undefined-version' to the vDSO ldflags
but this does not seem unreasonable to me.

 arch/x86/entry/vdso/vdso.lds.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/entry/vdso/vdso.lds.S b/arch/x86/entry/vdso/vdso.lds.S
index 4bf48462fca7..e8c60ae7a7c8 100644
--- a/arch/x86/entry/vdso/vdso.lds.S
+++ b/arch/x86/entry/vdso/vdso.lds.S
@@ -27,7 +27,9 @@ VERSION {
 		__vdso_time;
 		clock_getres;
 		__vdso_clock_getres;
+#ifdef CONFIG_X86_SGX
 		__vdso_sgx_enter_enclave;
+#endif
 	local: *;
 	};
 }

base-commit: f0c4d9fc9cc9462659728d168387191387e903cc
-- 
2.38.1