2022-07-13 17:41:54

by Nathan Chancellor

Subject: [PATCH] bpf, arm64: Mark dummy_tramp as global

When building with clang + CONFIG_CFI_CLANG=y, the following error
occurs at link time:

ld.lld: error: undefined symbol: dummy_tramp

dummy_tramp is declared globally in C but its definition in inline
assembly does not use .global, which prevents clang from properly
resolving the references to it when creating the CFI jump tables.

Mark dummy_tramp as global so that the reference can be properly
resolved.

Fixes: b2ad54e1533e ("bpf, arm64: Implement bpf_arch_text_poke() for arm64")
Link: https://github.com/ClangBuiltLinux/linux/issues/1661
Suggested-by: Sami Tolvanen <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
---
arch/arm64/net/bpf_jit_comp.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index fd1cb0d2aaa6..dcc572b7d4da 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -604,6 +604,7 @@ void dummy_tramp(void);

asm (
" .pushsection .text, \"ax\", @progbits\n"
+" .global dummy_tramp\n"
" .type dummy_tramp, %function\n"
"dummy_tramp:"
#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)

base-commit: ace2bee839e08df324cb320763258dfd72e6120e
--
2.37.1

2022-07-13 19:34:37

by Stanislav Fomichev

Subject: Re: [PATCH] bpf, arm64: Mark dummy_tramp as global

On Wed, Jul 13, 2022 at 10:35 AM Nathan Chancellor <[email protected]> wrote:
>
> When building with clang + CONFIG_CFI_CLANG=y, the following error
> occurs at link time:
>
> ld.lld: error: undefined symbol: dummy_tramp
>
> dummy_tramp is declared globally in C but its definition in inline
> assembly does not use .global, which prevents clang from properly
> resolving the references to it when creating the CFI jump tables.
>
> Mark dummy_tramp as global so that the reference can be properly
> resolved.
>
> Fixes: b2ad54e1533e ("bpf, arm64: Implement bpf_arch_text_poke() for arm64")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1661
> Suggested-by: Sami Tolvanen <[email protected]>
> Signed-off-by: Nathan Chancellor <[email protected]>

Reviewed-by: Stanislav Fomichev <[email protected]>

> ---
> arch/arm64/net/bpf_jit_comp.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index fd1cb0d2aaa6..dcc572b7d4da 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -604,6 +604,7 @@ void dummy_tramp(void);
>
> asm (
> " .pushsection .text, \"ax\", @progbits\n"
> +" .global dummy_tramp\n"
> " .type dummy_tramp, %function\n"
> "dummy_tramp:"
> #if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
>
> base-commit: ace2bee839e08df324cb320763258dfd72e6120e
> --
> 2.37.1
>

2022-07-14 15:38:41

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] bpf, arm64: Mark dummy_tramp as global

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[email protected]>:

On Wed, 13 Jul 2022 10:35:03 -0700 you wrote:
> When building with clang + CONFIG_CFI_CLANG=y, the following error
> occurs at link time:
>
> ld.lld: error: undefined symbol: dummy_tramp
>
> dummy_tramp is declared globally in C but its definition in inline
> assembly does not use .global, which prevents clang from properly
> resolving the references to it when creating the CFI jump tables.
>
> [...]

Here is the summary with links:
- bpf, arm64: Mark dummy_tramp as global
https://git.kernel.org/bpf/bpf-next/c/33f32e5072b6

You are awesome, thank you!
--
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