linux-kernel - Re: [PATCH bpf-next v9 3/4] bpf, arm64: Implement bpf_arch_text

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Date:   Mon, 18 Jul 2022 23:37:01 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Jon Hunter <jonathanh@...dia.com>, <bpf@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Will Deacon <will@...nel.org>, KP Singh <kpsingh@...nel.org>
CC:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...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>,
        "H . Peter Anvin" <hpa@...or.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        James Morse <james.morse@....com>,
        Hou Tao <houtao1@...wei.com>,
        Jason Wang <wangborong@...rlc.com>
Subject: Re: [PATCH bpf-next v9 3/4] bpf, arm64: Implement
 bpf_arch_text_poke() for arm64

On 7/18/2022 9:52 PM, Jon Hunter wrote:

[..]
> 
> This change appears to be causing the build to fail ...
> 
> /tmp/cc52xO0c.s: Assembler messages:
> /tmp/cc52xO0c.s:8: Error: operand 1 should be an integer register --
> `mov lr,x9'
> /tmp/cc52xO0c.s:7: Error: undefined symbol lr used as an immediate value
> make[2]: *** [scripts/Makefile.build:250: arch/arm64/net/bpf_jit_comp.o]
> Error 1
> make[1]: *** [scripts/Makefile.build:525: arch/arm64/net] Error 2
> 
> Let me know if you have any thoughts.
> 

Sorry for this failure, but I can't reproduce it.

I guess maybe your assembler doesn't recognize "lr". Could you give a
try to replace "lr" with "x30"?

 #if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
 "      bti j\n" /* dummy_tramp is called via "br x10" */
 #endif
-"      mov x10, lr\n"
-"      mov lr, x9\n"
+"      mov x10, x30\n"
+"      mov x30, x9\n"
 "      ret x10\n"
 "      .size dummy_tramp, .-dummy_tramp\n"
 "      .popsection\n

Thanks.

> Cheers
> Jon
>