linux-kernel - Re: [PATCH] riscv: hwprobe: do not produce frtace relocation

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Message-ID: <be1b8bb6-ae08-4173-9ce5-26f2acee5950@ghiti.fr>
Date: Tue, 26 Mar 2024 09:56:10 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Vladimir Isaev <vladimir.isaev@...tacore.com>, paul.walmsley@...ive.com,
 palmer@...belt.com, aou@...s.berkeley.edu, catalin.marinas@....com,
 evan@...osinc.com, nicolas@...sle.eu, tglx@...utronix.de,
 samitolvanen@...gle.com, masahiroy@...nel.org, maskray@...gle.com,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 guoren@...nel.org
Cc: Roman Artemev <roman.artemev@...tacore.com>
Subject: Re: [PATCH] riscv: hwprobe: do not produce frtace relocation

Hi Vladimir,

s/frtace/ftrace

On 13/03/2024 08:35, Vladimir Isaev wrote:
> 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@...tacore.com>
> Signed-off-by: Vladimir Isaev <vladimir.isaev@...tacore.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)


I did not find a way to remove those flags for all C files 
automatically, too bad. But then I noticed that we were the only 
architecture which does not check for dynamic relocations in vdso, so at 
least we'll fail loudly. I'll send a patch for that soon.

This should go into -fixes.

Anyway, you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex


>   
>   # Disable profiling and instrumentation for VDSO code
>   GCOV_PROFILE := n