linux-kernel - Re: [PATCH v1A 1/2] x86/fred: Fix build with clang

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Date: Tue, 30 Jan 2024 11:34:45 +0100
From: Borislav Petkov <bp@...en8.de>
To: Xin Li <xin3.li@...el.com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	luto@...nel.org, ravi.v.shankar@...el.com,
	andrew.cooper3@...rix.com
Subject: Re: [PATCH v1A 1/2] x86/fred: Fix build with clang

On Sun, Jan 28, 2024 at 10:45:21PM -0800, Xin Li wrote:
> Remove the .fill statement that referneces asm_fred_entrypoint_kernel()
> before it's defined, which breaks clang build.
> 
> Use the .org directive instead to fill "int3" into the memory between
> asm_fred_entrypoint_user() and asm_fred_entrypoint_kernel().
> 
> Fixes: 5e0636a41485 ("x86/fred: FRED entry/exit and dispatch code")
> Reported-by: Borislav Petkov (AMD) <bp@...en8.de>
> Link: https://lore.kernel.org/lkml/20240126100050.GAZbOC0g3Rlr6otZcT@fat_crate.local/
> Signed-off-by: Xin Li <xin3.li@...el.com>
> ---
> 
> Change since v1:
> * Use ".org ..., 0xcc" to fill "int3" into memory (H. Peter Anvin).
> ---
>  arch/x86/entry/entry_64_fred.S | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
> index eedf98de7538..a02bc6f3d2e6 100644
> --- a/arch/x86/entry/entry_64_fred.S
> +++ b/arch/x86/entry/entry_64_fred.S
> @@ -43,14 +43,12 @@ SYM_INNER_LABEL(asm_fred_exit_user, SYM_L_GLOBAL)
>  	_ASM_EXTABLE_TYPE(1b, asm_fred_entrypoint_user, EX_TYPE_ERETU)
>  SYM_CODE_END(asm_fred_entrypoint_user)
>  
> -.fill asm_fred_entrypoint_kernel - ., 1, 0xcc
> -
>  /*
>   * The new RIP value that FRED event delivery establishes is
>   * (IA32_FRED_CONFIG & ~FFFH) + 256 for events that occur in
>   * ring 0, i.e., asm_fred_entrypoint_user + 256.
>   */
> -	.org asm_fred_entrypoint_user + 256
> +	.org asm_fred_entrypoint_user + 256, 0xcc
>  SYM_CODE_START_NOALIGN(asm_fred_entrypoint_kernel)
>  	FRED_ENTER
>  	call	fred_entry_from_kernel
> -- 

Considering how we're still very early in the game, I'm going to fold
those into the respective patches and rebase so that we have as clean
a branch as possible.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette