Re: [PATCH v3 10/13] riscv: alternative: patch alternatives in the vDSO

[Conor Dooley]

Hey Jisheng,

On Thu, Jan 12, 2023 at 01:10:24AM +0800, Jisheng Zhang wrote:
> Make it possible to use alternatives in the vDSO, so that better
> implementations can be used if possible.
> 
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

FYI, from this patch onwards the rv32 build is broken.
Should be reproduceable with the in-tree rv32_defconfig.

Unfortunately no logs for you, I've got a CI bug to fix!

Thanks,
Conor.

> ---
>  arch/riscv/include/asm/vdso.h     |  4 ++++
>  arch/riscv/kernel/alternative.c   | 25 +++++++++++++++++++++++++
>  arch/riscv/kernel/vdso.c          |  5 -----
>  arch/riscv/kernel/vdso/vdso.lds.S |  7 +++++++
>  4 files changed, 36 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
> index a7644f46d0e5..f891478829a5 100644
> --- a/arch/riscv/include/asm/vdso.h
> +++ b/arch/riscv/include/asm/vdso.h
> @@ -28,8 +28,12 @@
>  #define COMPAT_VDSO_SYMBOL(base, name)						\
>  	(void __user *)((unsigned long)(base) + compat__vdso_##name##_offset)
>  
> +extern char compat_vdso_start[], compat_vdso_end[];
> +
>  #endif /* CONFIG_COMPAT */
>  
> +extern char vdso_start[], vdso_end[];
> +
>  #endif /* !__ASSEMBLY__ */
>  
>  #endif /* CONFIG_MMU */
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index 3d4f1f32c7f6..a883a309139f 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -11,7 +11,9 @@
>  #include <linux/cpu.h>
>  #include <linux/uaccess.h>
>  #include <asm/alternative.h>
> +#include <asm/module.h>
>  #include <asm/sections.h>
> +#include <asm/vdso.h>
>  #include <asm/vendorid_list.h>
>  #include <asm/sbi.h>
>  #include <asm/csr.h>
> @@ -160,6 +162,27 @@ static void __init_or_module _apply_alternatives(struct alt_entry *begin,
>  				stage);
>  }
>  
> +static void __init apply_vdso_alternatives(void)
> +{
> +	const struct elf64_hdr *hdr;
> +	const struct elf64_shdr *shdr;
> +	const struct elf64_shdr *alt;
> +	struct alt_entry *begin, *end;
> +
> +	hdr = (struct elf64_hdr *)vdso_start;
> +	shdr = (void *)hdr + hdr->e_shoff;
> +	alt = find_section(hdr, shdr, ".alternative");
> +	if (!alt)
> +		return;
> +
> +	begin = (void *)hdr + alt->sh_offset,
> +	end = (void *)hdr + alt->sh_offset + alt->sh_size,
> +
> +	_apply_alternatives((struct alt_entry *)begin,
> +			    (struct alt_entry *)end,
> +			    RISCV_ALTERNATIVES_BOOT);
> +}
> +
>  void __init apply_boot_alternatives(void)
>  {
>  	/* If called on non-boot cpu things could go wrong */
> @@ -168,6 +191,8 @@ void __init apply_boot_alternatives(void)
>  	_apply_alternatives((struct alt_entry *)__alt_start,
>  			    (struct alt_entry *)__alt_end,
>  			    RISCV_ALTERNATIVES_BOOT);
> +
> +	apply_vdso_alternatives();
>  }
>  
>  /*
> diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
> index e410275918ac..4e631c098f4d 100644
> --- a/arch/riscv/kernel/vdso.c
> +++ b/arch/riscv/kernel/vdso.c
> @@ -22,11 +22,6 @@ struct vdso_data {
>  };
>  #endif
>  
> -extern char vdso_start[], vdso_end[];
> -#ifdef CONFIG_COMPAT
> -extern char compat_vdso_start[], compat_vdso_end[];
> -#endif
> -
>  enum vvar_pages {
>  	VVAR_DATA_PAGE_OFFSET,
>  	VVAR_TIMENS_PAGE_OFFSET,
> diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
> index 150b1a572e61..4a0606633290 100644
> --- a/arch/riscv/kernel/vdso/vdso.lds.S
> +++ b/arch/riscv/kernel/vdso/vdso.lds.S
> @@ -40,6 +40,13 @@ SECTIONS
>  	. = 0x800;
>  	.text		: { *(.text .text.*) }		:text
>  
> +	. = ALIGN(4);
> +	.alternative : {
> +		__alt_start = .;
> +		*(.alternative)
> +		__alt_end = .;
> +	}
> +
>  	.data		: {
>  		*(.got.plt) *(.got)
>  		*(.data .data.* .gnu.linkonce.d.*)
> -- 
> 2.38.1
>

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