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From: Vladimir Isaev <vladimir.isaev@syntacore.com>
To: <paul.walmsley@sifive.com>, <palmer@dabbelt.com>, <aou@eecs.berkeley.edu>,
	<catalin.marinas@arm.com>, <evan@rivosinc.com>, <nicolas@fjasle.eu>,
	<tglx@linutronix.de>, <samitolvanen@google.com>, <masahiroy@kernel.org>,
	<maskray@google.com>, <linux-riscv@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <guoren@kernel.org>
CC: Vladimir Isaev <vladimir.isaev@syntacore.com>, Roman Artemev
	<roman.artemev@syntacore.com>
Subject: [PATCH] riscv: hwprobe: do not produce frtace relocation
Date: Wed, 13 Mar 2024 10:35:46 +0300
Message-ID: <20240313085843.17661-1-vladimir.isaev@syntacore.com>
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Such relocation causes crash of android linker similar to one
described in commit e05d57dcb8c7
("riscv: Fixup __vdso_gettimeofday broke dynamic ftrace").

Looks like this relocation is added by CONFIG_DYNAMIC_FTRACE which is
disabled in the default android kernel.

Before:

readelf -rW arch/riscv/kernel/vdso/vdso.so:

Relocation section '.rela.dyn' at offset 0xd00 contains 1 entry:
    Offset             Info             Type
0000000000000d20  0000000000000003 R_RISCV_RELATIVE

objdump:
0000000000000c86 <__vdso_riscv_hwprobe@@LINUX_4.15>:
 c86:   0001                    nop
 c88:   0001                    nop
 c8a:   0001                    nop
 c8c:   0001                    nop
 c8e:   e211                    bnez    a2,c92 <__vdso_riscv_hwprobe...

After:
readelf -rW arch/riscv/kernel/vdso/vdso.so:

There are no relocations in this file.

objdump:
0000000000000c86 <__vdso_riscv_hwprobe@@LINUX_4.15>:
 c86:   e211                    bnez    a2,c8a <__vdso_riscv_hwprobe...
 c88:   c6b9                    beqz    a3,cd6 <__vdso_riscv_hwprobe...
 c8a:   e739                    bnez    a4,cd8 <__vdso_riscv_hwprobe...
 c8c:   ffffd797                auipc   a5,0xffffd

Also disable SCS since it also should not be available in vdso.

Fixes: aa5af0aa90ba ("RISC-V: Add hwprobe vDSO function and data")
Signed-off-by: Roman Artemev <roman.artemev@syntacore.com>
Signed-off-by: Vladimir Isaev <vladimir.isaev@syntacore.com>
---
 arch/riscv/kernel/vdso/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 9b517fe1b8a8..272c431ac5b9 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -37,6 +37,7 @@ endif
 
 # Disable -pg to prevent insert call site
 CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
+CFLAGS_REMOVE_hwprobe.o = $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS)
 
 # Disable profiling and instrumentation for VDSO code
 GCOV_PROFILE := n
-- 
2.43.0