[3/3] riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr
Commit Message
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(-)
Comments
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
@@ -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);