[PATCH 1/2] powerpc/vmlinux.lds: Explicitly retain .gnu.hash

[PATCH 1/2] powerpc/vmlinux.lds: Explicitly retain .gnu.hash

[Michael Ellerman]

Relocatable kernel builds produce a warning about .gnu.hash being an
orphan section:

  ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'

If we try to discard it the build fails:

  ld -EL -m elf64lppc -pie --orphan-handling=warn --build-id -o
    .tmp_vmlinux1 -T ./arch/powerpc/kernel/vmlinux.lds --whole-archive
    arch/powerpc/kernel/head_64.o arch/powerpc/kernel/entry_64.o
    ...
    sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive
    --start-group lib/lib.a --end-group
  ld: could not find section .gnu.hash

So add an entry to explicitly retain it, as we do for .hash.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/vmlinux.lds.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index b4c89a1acebb..31a0f201fb6f 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -256,6 +256,7 @@ SECTIONS
 		*(.dynamic)
 	}
 	.hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) }
+	.gnu.hash : AT(ADDR(.gnu.hash) - LOAD_OFFSET) { *(.gnu.hash) }
 	.interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }
 	.rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
 	{
-- 
2.21.1

[PATCH 2/2] powerpc/vmlinux.lds: Discard .interp section

[Michael Ellerman]

The .interp section specifies which "interpreter", ie. dynamic loader,
the kernel requests. But that doesn't make any sense, the kernel is
not a regular binary that is run with an interpreter.

The content seems to be some default value, this file doesn't even
exist on my system:
  00000000  2f 75 73 72 2f 6c 69 62  2f 6c 64 2e 73 6f 2e 31  |/usr/lib/ld.so.1|

So the section serves no useful purpose and consumes a small amount of
space.

Also Alan Modra says we "likely could discard" it, so do so.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/vmlinux.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 31a0f201fb6f..619ffbaf72ad 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -257,7 +257,6 @@ SECTIONS
 	}
 	.hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) }
 	.gnu.hash : AT(ADDR(.gnu.hash) - LOAD_OFFSET) { *(.gnu.hash) }
-	.interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }
 	.rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
 	{
 		__rela_dyn_start = .;
@@ -370,5 +369,6 @@ SECTIONS
 		*(.gnu.version*)
 		*(.gnu.attributes)
 		*(.eh_frame)
+		*(.interp)
 	}
 }
-- 
2.21.1

Re: [PATCH 1/2] powerpc/vmlinux.lds: Explicitly retain .gnu.hash

[Alan Modra]

On Thu, Feb 27, 2020 at 03:59:32PM +1100, Michael Ellerman wrote:
> Relocatable kernel builds produce a warning about .gnu.hash being an
> orphan section:
> 
>   ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'
> 
> If we try to discard it the build fails:
> 
>   ld -EL -m elf64lppc -pie --orphan-handling=warn --build-id -o
>     .tmp_vmlinux1 -T ./arch/powerpc/kernel/vmlinux.lds --whole-archive
>     arch/powerpc/kernel/head_64.o arch/powerpc/kernel/entry_64.o
>     ...
>     sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive
>     --start-group lib/lib.a --end-group
>   ld: could not find section .gnu.hash
> 
> So add an entry to explicitly retain it, as we do for .hash.

Looks fine to me.  You can also pass --hash-style=sysv to ld (since
binutils-2.18) to disable generation of .gnu.hash.

> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/kernel/vmlinux.lds.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index b4c89a1acebb..31a0f201fb6f 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -256,6 +256,7 @@ SECTIONS
>  		*(.dynamic)
>  	}
>  	.hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) }
> +	.gnu.hash : AT(ADDR(.gnu.hash) - LOAD_OFFSET) { *(.gnu.hash) }
>  	.interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }
>  	.rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
>  	{
> -- 
> 2.21.1

-- 
Alan Modra
Australia Development Lab, IBM

Re: [PATCH 2/2] powerpc/vmlinux.lds: Discard .interp section

[Alan Modra]

On Thu, Feb 27, 2020 at 03:59:33PM +1100, Michael Ellerman wrote:
> The .interp section specifies which "interpreter", ie. dynamic loader,
> the kernel requests. But that doesn't make any sense, the kernel is
> not a regular binary that is run with an interpreter.
> 
> The content seems to be some default value, this file doesn't even
> exist on my system:
>   00000000  2f 75 73 72 2f 6c 69 62  2f 6c 64 2e 73 6f 2e 31  |/usr/lib/ld.so.1|
> 
> So the section serves no useful purpose and consumes a small amount of
> space.
> 
> Also Alan Modra says we "likely could discard" it, so do so.

Yes, but you ought to check with the mimimum required binutils.  It is
quite possible that an older linker will blow up.

If the minimum required binutils is at least binutils-2.26 then
passing --no-dynamic-linker to ld is a more elegant solution.

> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/kernel/vmlinux.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 31a0f201fb6f..619ffbaf72ad 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -257,7 +257,6 @@ SECTIONS
>  	}
>  	.hash : AT(ADDR(.hash) - LOAD_OFFSET) { *(.hash) }
>  	.gnu.hash : AT(ADDR(.gnu.hash) - LOAD_OFFSET) { *(.gnu.hash) }
> -	.interp : AT(ADDR(.interp) - LOAD_OFFSET) { *(.interp) }
>  	.rela.dyn : AT(ADDR(.rela.dyn) - LOAD_OFFSET)
>  	{
>  		__rela_dyn_start = .;
> @@ -370,5 +369,6 @@ SECTIONS
>  		*(.gnu.version*)
>  		*(.gnu.attributes)
>  		*(.eh_frame)
> +		*(.interp)
>  	}
>  }
> -- 
> 2.21.1

-- 
Alan Modra
Australia Development Lab, IBM

Re: [PATCH 2/2] powerpc/vmlinux.lds: Discard .interp section

[Michael Ellerman]

Alan Modra <amodra@gmail.com> writes:
> On Thu, Feb 27, 2020 at 03:59:33PM +1100, Michael Ellerman wrote:
>> The .interp section specifies which "interpreter", ie. dynamic loader,
>> the kernel requests. But that doesn't make any sense, the kernel is
>> not a regular binary that is run with an interpreter.
>> 
>> The content seems to be some default value, this file doesn't even
>> exist on my system:
>>   00000000  2f 75 73 72 2f 6c 69 62  2f 6c 64 2e 73 6f 2e 31  |/usr/lib/ld.so.1|
>> 
>> So the section serves no useful purpose and consumes a small amount of
>> space.
>> 
>> Also Alan Modra says we "likely could discard" it, so do so.
>
> Yes, but you ought to check with the mimimum required binutils.  It is
> quite possible that an older linker will blow up.

OK, I guess I'll have to test.

> If the minimum required binutils is at least binutils-2.26 then
> passing --no-dynamic-linker to ld is a more elegant solution.

The current minimum is 2.21, though there's talk of increasing it to
2.23.

cheers

Re: [PATCH 1/2] powerpc/vmlinux.lds: Explicitly retain .gnu.hash

[Michael Ellerman]

Alan Modra <amodra@gmail.com> writes:
> On Thu, Feb 27, 2020 at 03:59:32PM +1100, Michael Ellerman wrote:
>> Relocatable kernel builds produce a warning about .gnu.hash being an
>> orphan section:
>> 
>>   ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'
>> 
>> If we try to discard it the build fails:
>> 
>>   ld -EL -m elf64lppc -pie --orphan-handling=warn --build-id -o
>>     .tmp_vmlinux1 -T ./arch/powerpc/kernel/vmlinux.lds --whole-archive
>>     arch/powerpc/kernel/head_64.o arch/powerpc/kernel/entry_64.o
>>     ...
>>     sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive
>>     --start-group lib/lib.a --end-group
>>   ld: could not find section .gnu.hash
>> 
>> So add an entry to explicitly retain it, as we do for .hash.
>
> Looks fine to me.  You can also pass --hash-style=sysv to ld (since
> binutils-2.18) to disable generation of .gnu.hash.

Our current minimum is 2.21, so that's probably 5-10 years away :)

cheers

Re: [PATCH 1/2] powerpc/vmlinux.lds: Explicitly retain .gnu.hash

[Michael Ellerman]

On Thu, 2020-02-27 at 04:59:32 UTC, Michael Ellerman wrote:
> Relocatable kernel builds produce a warning about .gnu.hash being an
> orphan section:
> 
>   ld: warning: orphan section `.gnu.hash' from `linker stubs' being placed in section `.gnu.hash'
> 
> If we try to discard it the build fails:
> 
>   ld -EL -m elf64lppc -pie --orphan-handling=warn --build-id -o
>     .tmp_vmlinux1 -T ./arch/powerpc/kernel/vmlinux.lds --whole-archive
>     arch/powerpc/kernel/head_64.o arch/powerpc/kernel/entry_64.o
>     ...
>     sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive
>     --start-group lib/lib.a --end-group
>   ld: could not find section .gnu.hash
> 
> So add an entry to explicitly retain it, as we do for .hash.
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/ead983604c5a390f1e3ce085945b60e82f08dbbe

cheers