I believe the hardcoded 0x800 and related comments come from the long
history VDSO_TEXT_OFFSET in x86 vdso code, but commit 5b9304933730
("x86 vDSO: generate vdso-syms.lds") and commit f6b46ebf904f ("x86
vDSO: new layout") removes the comment and hard coding for x86.

Similar as x86 and other arch, riscv doesn't need the rigid layout
using VDSO_TEXT_OFFSET since it "no longer matters to the kernel".
so we could remove the hard coding now, and removing it brings a
small vdso.so and aligns with other architectures.

Also, having enough separation between data and text is important for
I-cache, so similar as x86, move .note, .eh_frame_hdr, and .eh_frame
between .rodata and .text.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 arch/riscv/kernel/vdso/vdso.lds.S | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index 671aa21769bc..cbe2a179331d 100644
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -23,12 +23,8 @@ SECTIONS
 	.gnu.version_d	: { *(.gnu.version_d) }
 	.gnu.version_r	: { *(.gnu.version_r) }
 
-	.note		: { *(.note.*) }		:text	:note
 	.dynamic	: { *(.dynamic) }		:text	:dynamic
 
-	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
-	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
-
 	.rodata		: {
 		*(.rodata .rodata.* .gnu.linkonce.r.*)
 		*(.got.plt) *(.got)
@@ -37,13 +33,16 @@ SECTIONS
 		*(.bss .bss.* .gnu.linkonce.b.*)
 	}
 
+	.note		: { *(.note.*) }		:text	:note
+
+	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
+	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
+
 	/*
-	 * This linker script is used both with -r and with -shared.
-	 * For the layouts to match, we need to skip more than enough
-	 * space for the dynamic symbol table, etc. If this amount is
-	 * insufficient, ld -shared will error; simply increase it here.
+	 * Text is well-separated from actual data: there's plenty of
+	 * stuff that isn't used at runtime in between.
 	 */
-	. = 0x800;
+	. = ALIGN(16);
 	.text		: { *(.text .text.*) }		:text
 
 	. = ALIGN(4);
-- 
2.40.1

On Thu, Jul 27, 2023 at 01:30:24AM +0800, Jisheng Zhang wrote:
> I believe the hardcoded 0x800 and related comments come from the long
> history VDSO_TEXT_OFFSET in x86 vdso code, but commit 5b9304933730
> ("x86 vDSO: generate vdso-syms.lds") and commit f6b46ebf904f ("x86
> vDSO: new layout") removes the comment and hard coding for x86.
> 
> Similar as x86 and other arch, riscv doesn't need the rigid layout
> using VDSO_TEXT_OFFSET since it "no longer matters to the kernel".
> so we could remove the hard coding now, and removing it brings a
> small vdso.so and aligns with other architectures.
> 
> Also, having enough separation between data and text is important for
> I-cache, so similar as x86, move .note, .eh_frame_hdr, and .eh_frame
> between .rodata and .text.
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/kernel/vdso/vdso.lds.S | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
> index 671aa21769bc..cbe2a179331d 100644
> --- a/arch/riscv/kernel/vdso/vdso.lds.S
> +++ b/arch/riscv/kernel/vdso/vdso.lds.S
> @@ -23,12 +23,8 @@ SECTIONS
>  	.gnu.version_d	: { *(.gnu.version_d) }
>  	.gnu.version_r	: { *(.gnu.version_r) }
>  
> -	.note		: { *(.note.*) }		:text	:note
>  	.dynamic	: { *(.dynamic) }		:text	:dynamic
>  
> -	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
> -	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
> -
>  	.rodata		: {
>  		*(.rodata .rodata.* .gnu.linkonce.r.*)
>  		*(.got.plt) *(.got)
> @@ -37,13 +33,16 @@ SECTIONS
>  		*(.bss .bss.* .gnu.linkonce.b.*)
>  	}
>  
> +	.note		: { *(.note.*) }		:text	:note
> +
> +	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
> +	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
> +
>  	/*
> -	 * This linker script is used both with -r and with -shared.
> -	 * For the layouts to match, we need to skip more than enough
> -	 * space for the dynamic symbol table, etc. If this amount is
> -	 * insufficient, ld -shared will error; simply increase it here.
> +	 * Text is well-separated from actual data: there's plenty of
> +	 * stuff that isn't used at runtime in between.
>  	 */
> -	. = 0x800;
> +	. = ALIGN(16);
>  	.text		: { *(.text .text.*) }		:text
>  
>  	. = ALIGN(4);
> -- 
> 2.40.1
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks,
drew