[PATCH] arm64: Change the location of DISCARDS

[PATCH] arm64: Change the location of DISCARDS

[Youling Tang]

In the include/asm-generic/vmlinux.lds.h file, the "must be the last"
comment indicates that DISCARDS should be placed in the last position
of SECTIONS, like x86, mips, riscv, etc.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
---
 arch/arm64/kernel/vmlinux.lds.S | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 1bda604..bf31074 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -109,12 +109,6 @@ SECTIONS
 	 * matching the same input section name.  There is no documented
 	 * order of matching.
 	 */
-	DISCARDS
-	/DISCARD/ : {
-		*(.interp .dynamic)
-		*(.dynsym .dynstr .hash .gnu.hash)
-	}
-
 	. = KIMAGE_VADDR;
 
 	.head.text : {
@@ -284,6 +278,13 @@ SECTIONS
 
 	.data.rel.ro : { *(.data.rel.ro) }
 	ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!")
+
+	/* Sections to be discarded */
+	DISCARDS
+	/DISCARD/ : {
+		*(.interp .dynamic)
+		*(.dynsym .dynstr .hash .gnu.hash)
+	}
 }
 
 #include "image-vars.h"
-- 
2.1.0

Re: [PATCH] arm64: Change the location of DISCARDS

[Will Deacon]

On Wed, Nov 04, 2020 at 06:48:52PM +0800, Youling Tang wrote:
> In the include/asm-generic/vmlinux.lds.h file, the "must be the last"
> comment indicates that DISCARDS should be placed in the last position
> of SECTIONS, like x86, mips, riscv, etc.
> 
> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
> ---
>  arch/arm64/kernel/vmlinux.lds.S | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)

Why does this section need to be last?

Will

Re: [PATCH] arm64: Change the location of DISCARDS

[tangyouling]

Hi, Will

In the include/asm-generic/vmlinux.lds.h:978, the description is as follows:
DISCARDS must be the last of output section definitions so that such archs
put those in earlier section definitions.

Thanks,

Youling


On 11/06/2020 05:47 AM, Will Deacon wrote:
> In the include/asm-generic/vmlinux.lds.h file

Re: [PATCH] arm64: Change the location of DISCARDS

[Will Deacon]

On Fri, Nov 06, 2020 at 09:06:42AM +0800, tangyouling wrote:
> In the include/asm-generic/vmlinux.lds.h:978, the description is as follows:
> DISCARDS must be the last of output section definitions so that such archs
> put those in earlier section definitions.

Sure, I see that text, but I don't get why it matters. It would be nice to
have some rationale as to what could go wrong if they aren't at the end,
so we can improve that comment and avoid the inevitable regression in the
future when things get shuffled around.

Will

Re: [PATCH] arm64: Change the location of DISCARDS

[Catalin Marinas]

On Fri, Nov 06, 2020 at 09:07:38AM +0000, Will Deacon wrote:
> On Fri, Nov 06, 2020 at 09:06:42AM +0800, tangyouling wrote:
> > In the include/asm-generic/vmlinux.lds.h:978, the description is as follows:
> > DISCARDS must be the last of output section definitions so that such archs
> > put those in earlier section definitions.
> 
> Sure, I see that text, but I don't get why it matters. It would be nice to
> have some rationale as to what could go wrong if they aren't at the end,
> so we can improve that comment and avoid the inevitable regression in the
> future when things get shuffled around.

Maybe on other architectures or some old toolchains made a difference in
the resulting binary image size. It doesn't seem to be the case for
arm64.

-- 
Catalin