[RESEND PATCH 0/3] riscv: vdso.lds.S: some improvement

[RESEND PATCH 0/3] riscv: vdso.lds.S: some improvement

[Jisheng Zhang]

This series renews one of my last year RFC patch[1], tries to improve
the vdso layout a bit. 

patch1 removes useless symbols
patch2 merges .data section of vdso into .rodata because they are
readonly
patch3 is the real renew patch, it removes hardcoded 0x800 .text start
addr. But I rewrite the commit msg per Andrew's suggestions and move
move .note, .eh_frame_hdr, and .eh_frame between .rodata and .text to
keep the actual code well away from the non-instruction data.

Link: https://lore.kernel.org/linux-riscv/20221123161805.1579-1-jszhang@kernel.org/ [1]

Jisheng Zhang (3):
  riscv: vdso.lds.S: drop __alt_start and __alt_end symbols
  riscv: vdso.lds.S: merge .data section into .rodata section
  riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr

 arch/riscv/kernel/vdso/vdso.lds.S | 30 +++++++++++++-----------------
 1 file changed, 13 insertions(+), 17 deletions(-)

-- 
2.40.1

[RESEND PATCH 1/3] riscv: vdso.lds.S: drop __alt_start and __alt_end symbols

[Jisheng Zhang]

These two symbols are not used, remove them.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
---
 arch/riscv/kernel/vdso/vdso.lds.S | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index 82ce64900f3d..d43fd7c7dd11 100644
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -42,9 +42,7 @@ SECTIONS
 
 	. = ALIGN(4);
 	.alternative : {
-		__alt_start = .;
 		*(.alternative)
-		__alt_end = .;
 	}
 
 	.data		: {
-- 
2.40.1

[RESEND PATCH 2/3] riscv: vdso.lds.S: merge .data section into .rodata section

[Jisheng Zhang]

The .data section doesn't need to be separate from .rodata section,
they are both readonly.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
---
 arch/riscv/kernel/vdso/vdso.lds.S | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index d43fd7c7dd11..671aa21769bc 100644
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -29,7 +29,13 @@ SECTIONS
 	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr
 	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
 
-	.rodata		: { *(.rodata .rodata.* .gnu.linkonce.r.*) }
+	.rodata		: {
+		*(.rodata .rodata.* .gnu.linkonce.r.*)
+		*(.got.plt) *(.got)
+		*(.data .data.* .gnu.linkonce.d.*)
+		*(.dynbss)
+		*(.bss .bss.* .gnu.linkonce.b.*)
+	}
 
 	/*
 	 * This linker script is used both with -r and with -shared.
@@ -44,13 +50,6 @@ SECTIONS
 	.alternative : {
 		*(.alternative)
 	}
-
-	.data		: {
-		*(.got.plt) *(.got)
-		*(.data .data.* .gnu.linkonce.d.*)
-		*(.dynbss)
-		*(.bss .bss.* .gnu.linkonce.b.*)
-	}
 }
 
 /*
-- 
2.40.1

[RESEND PATCH 3/3] riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr

[Jisheng Zhang]

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>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
---
 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

Re: [RESEND PATCH 0/3] riscv: vdso.lds.S: some improvement

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Tue, 12 Sep 2023 15:20:12 +0800 you wrote:
> This series renews one of my last year RFC patch[1], tries to improve
> the vdso layout a bit.
> 
> patch1 removes useless symbols
> patch2 merges .data section of vdso into .rodata because they are
> readonly
> patch3 is the real renew patch, it removes hardcoded 0x800 .text start
> addr. But I rewrite the commit msg per Andrew's suggestions and move
> move .note, .eh_frame_hdr, and .eh_frame between .rodata and .text to
> keep the actual code well away from the non-instruction data.
> 
> [...]

Here is the summary with links:
  - [RESEND,1/3] riscv: vdso.lds.S: drop __alt_start and __alt_end symbols
    https://git.kernel.org/riscv/c/ddcc7d9bf531
  - [RESEND,2/3] riscv: vdso.lds.S: merge .data section into .rodata section
    https://git.kernel.org/riscv/c/49cfbdc21faf
  - [RESEND,3/3] riscv: vdso.lds.S: remove hardcoded 0x800 .text start addr
    https://git.kernel.org/riscv/c/8f8c1ff879fa

You are awesome, thank you!
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