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

Conor Dooley
2023-01-12T07:49:12Z

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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@kernel.org>
> Reviewed-by: Guo Ren <guoren@kernel.org>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

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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