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* [PATCH 0/1] x86/boot: lld fix
@ 2020-05-20 22:56 Arvind Sankar
  2020-05-20 22:56 ` [PATCH 1/1] x86/boot: Add .text.startup to setup.ld Arvind Sankar
  2020-05-20 23:33 ` [PATCH 0/1] x86/boot: lld fix Arvind Sankar
  0 siblings, 2 replies; 6+ messages in thread
From: Arvind Sankar @ 2020-05-20 22:56 UTC (permalink / raw)
  To: clang-built-linux, x86; +Cc: Fangrui Song, Nick Desaulniers, linux-kernel

arch/x86/boot/setup.elf currently has an orphan section .text.startup,
and lld git as of ebf14d9b6d8b is breaking on 64-bit due to what seems
to be a change in behavior on orphan section placement (details in patch
commit message).

I'm not sure if this was an intentional change in lld, but it seems like
a good idea to explicitly include .text.startup anyway.

Arvind Sankar (1):
  x86/boot: Add .text.startup to setup.ld

 arch/x86/boot/setup.ld | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.26.2


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH 1/1] x86/boot: Add .text.startup to setup.ld
  2020-05-20 22:56 [PATCH 0/1] x86/boot: lld fix Arvind Sankar
@ 2020-05-20 22:56 ` Arvind Sankar
  2020-05-20 23:33 ` [PATCH 0/1] x86/boot: lld fix Arvind Sankar
  1 sibling, 0 replies; 6+ messages in thread
From: Arvind Sankar @ 2020-05-20 22:56 UTC (permalink / raw)
  To: clang-built-linux, x86; +Cc: Fangrui Song, Nick Desaulniers, linux-kernel

gcc puts the main function into .text.startup when compiled with -Os (or
-O2). This results in arch/x86/boot/main.c having a .text.startup
section which is currently not included explicitly in the linker script
setup.ld in the same directory.

The BFD linker places this orphan section immediately after .text, so
this still works. However, LLD git, on 64-bit only, is choosing to place
it immediately after the .bstext section instead (this is the first code
section). This plays havoc with the section layout that setup.elf
requires to create the setup header:

    LD      arch/x86/boot/setup.elf
  ld.lld: error: section .text.startup file range overlaps with .header
  >>> .text.startup range is [0x200040, 0x2001FE]
  >>> .header range is [0x2001EF, 0x20026B]

  ld.lld: error: section .header file range overlaps with .bsdata
  >>> .header range is [0x2001EF, 0x20026B]
  >>> .bsdata range is [0x2001FF, 0x200398]

  ld.lld: error: section .bsdata file range overlaps with .entrytext
  >>> .bsdata range is [0x2001FF, 0x200398]
  >>> .entrytext range is [0x20026C, 0x2002D3]

  ld.lld: error: section .text.startup virtual address range overlaps
  with .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header virtual address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata virtual address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

  ld.lld: error: section .text.startup load address range overlaps with
  .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header load address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata load address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

Explicitly pull .text.startup into the .text output section to avoid
this.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
 arch/x86/boot/setup.ld | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
index 24c95522f231..ed60abcdb089 100644
--- a/arch/x86/boot/setup.ld
+++ b/arch/x86/boot/setup.ld
@@ -20,7 +20,7 @@ SECTIONS
 	.initdata	: { *(.initdata) }
 	__end_init = .;
 
-	.text		: { *(.text) }
+	.text		: { *(.text.startup) *(.text) }
 	.text32		: { *(.text32) }
 
 	. = ALIGN(16);
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [PATCH 0/1] x86/boot: lld fix
  2020-05-20 22:56 [PATCH 0/1] x86/boot: lld fix Arvind Sankar
  2020-05-20 22:56 ` [PATCH 1/1] x86/boot: Add .text.startup to setup.ld Arvind Sankar
@ 2020-05-20 23:33 ` Arvind Sankar
  2020-05-21  2:12   ` Fangrui Song
  1 sibling, 1 reply; 6+ messages in thread
From: Arvind Sankar @ 2020-05-20 23:33 UTC (permalink / raw)
  To: Arvind Sankar
  Cc: clang-built-linux, x86, Fangrui Song, Nick Desaulniers, linux-kernel

On Wed, May 20, 2020 at 06:56:53PM -0400, Arvind Sankar wrote:
> arch/x86/boot/setup.elf currently has an orphan section .text.startup,
> and lld git as of ebf14d9b6d8b is breaking on 64-bit due to what seems
> to be a change in behavior on orphan section placement (details in patch
> commit message).
> 
> I'm not sure if this was an intentional change in lld, but it seems like
> a good idea to explicitly include .text.startup anyway.
> 
> Arvind Sankar (1):
>   x86/boot: Add .text.startup to setup.ld
> 
>  arch/x86/boot/setup.ld | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> -- 
> 2.26.2
> 

Actually I'm not sure this is a recent change. I updated to the git tip
because on my system (gentoo with gcc-10), lld-10.0.0 segfaults when
trying to link the compressed kernel, and updating to lld git fixed
that. So I previously probably didn't get to the stage where it links
setup.elf.

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH 0/1] x86/boot: lld fix
  2020-05-20 23:33 ` [PATCH 0/1] x86/boot: lld fix Arvind Sankar
@ 2020-05-21  2:12   ` Fangrui Song
  2020-05-21 15:20     ` Arvind Sankar
  2020-05-21 15:24     ` [PATCH v2] x86/boot: Add .text.startup to setup.ld Arvind Sankar
  0 siblings, 2 replies; 6+ messages in thread
From: Fangrui Song @ 2020-05-21  2:12 UTC (permalink / raw)
  To: Arvind Sankar; +Cc: clang-built-linux, x86, Nick Desaulniers, linux-kernel

On 2020-05-20, Arvind Sankar wrote:
>On Wed, May 20, 2020 at 06:56:53PM -0400, Arvind Sankar wrote:
>> arch/x86/boot/setup.elf currently has an orphan section .text.startup,
>> and lld git as of ebf14d9b6d8b is breaking on 64-bit due to what seems
>> to be a change in behavior on orphan section placement (details in patch
>> commit message).
>>
>> I'm not sure if this was an intentional change in lld, but it seems like
>> a good idea to explicitly include .text.startup anyway.
>>
>> Arvind Sankar (1):
>>   x86/boot: Add .text.startup to setup.ld
>>
>>  arch/x86/boot/setup.ld | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --
>> 2.26.2
>>

I found your PATCH 1/1 on https://lkml.org/lkml/2020/5/20/1491 

-	.text		: { *(.text) }
+	.text		: { *(.text.startup) *(.text) }

The LLD behavior change was introduced in
https://reviews.llvm.org/D75225 (will be included in 11.0.0)
It was intended to match GNU ld.

But yes, orphan section placement is still different in the two linkers.

Placing .text.startup before .text seems good.
In GNU ld's internal linker script (ld --verbose),
.text.startup is placed before .text

Reviewed-by: Fangrui Song <maskray@google.com>

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH 0/1] x86/boot: lld fix
  2020-05-21  2:12   ` Fangrui Song
@ 2020-05-21 15:20     ` Arvind Sankar
  2020-05-21 15:24     ` [PATCH v2] x86/boot: Add .text.startup to setup.ld Arvind Sankar
  1 sibling, 0 replies; 6+ messages in thread
From: Arvind Sankar @ 2020-05-21 15:20 UTC (permalink / raw)
  To: Fangrui Song
  Cc: Arvind Sankar, clang-built-linux, x86, Nick Desaulniers, linux-kernel

On Wed, May 20, 2020 at 07:12:17PM -0700, Fangrui Song wrote:
> On 2020-05-20, Arvind Sankar wrote:
> >On Wed, May 20, 2020 at 06:56:53PM -0400, Arvind Sankar wrote:
> >> arch/x86/boot/setup.elf currently has an orphan section .text.startup,
> >> and lld git as of ebf14d9b6d8b is breaking on 64-bit due to what seems
> >> to be a change in behavior on orphan section placement (details in patch
> >> commit message).
> >>
> >> I'm not sure if this was an intentional change in lld, but it seems like
> >> a good idea to explicitly include .text.startup anyway.
> >>
> >> Arvind Sankar (1):
> >>   x86/boot: Add .text.startup to setup.ld
> >>
> >>  arch/x86/boot/setup.ld | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> --
> >> 2.26.2
> >>
> 
> I found your PATCH 1/1 on https://lkml.org/lkml/2020/5/20/1491 
> 
> -	.text		: { *(.text) }
> +	.text		: { *(.text.startup) *(.text) }
> 
> The LLD behavior change was introduced in
> https://reviews.llvm.org/D75225 (will be included in 11.0.0)
> It was intended to match GNU ld.
> 
> But yes, orphan section placement is still different in the two linkers.
> 
> Placing .text.startup before .text seems good.
> In GNU ld's internal linker script (ld --verbose),
> .text.startup is placed before .text
> 
> Reviewed-by: Fangrui Song <maskray@google.com>

Thanks. I'll reword the commit message to include a reference to that
change. It's also not just 64-bit, on 32-bit it currently fails before
it gets around to linking setup.elf due to the text relocs issues,
that's why this one doesn't show up, but they are in fact at least
consistent.

^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH v2] x86/boot: Add .text.startup to setup.ld
  2020-05-21  2:12   ` Fangrui Song
  2020-05-21 15:20     ` Arvind Sankar
@ 2020-05-21 15:24     ` Arvind Sankar
  1 sibling, 0 replies; 6+ messages in thread
From: Arvind Sankar @ 2020-05-21 15:24 UTC (permalink / raw)
  To: x86; +Cc: Fangrui Song, Nick Desaulniers, clang-built-linux, linux-kernel

gcc puts the main function into .text.startup when compiled with -Os (or
-O2). This results in arch/x86/boot/main.c having a .text.startup
section which is currently not included explicitly in the linker script
setup.ld in the same directory.

The BFD linker places this orphan section immediately after .text, so
this still works. However, LLD git, since [1], is choosing to place it
immediately after the .bstext section instead (this is the first code
section). This plays havoc with the section layout that setup.elf
requires to create the setup header, for eg on 64-bit:

    LD      arch/x86/boot/setup.elf
  ld.lld: error: section .text.startup file range overlaps with .header
  >>> .text.startup range is [0x200040, 0x2001FE]
  >>> .header range is [0x2001EF, 0x20026B]

  ld.lld: error: section .header file range overlaps with .bsdata
  >>> .header range is [0x2001EF, 0x20026B]
  >>> .bsdata range is [0x2001FF, 0x200398]

  ld.lld: error: section .bsdata file range overlaps with .entrytext
  >>> .bsdata range is [0x2001FF, 0x200398]
  >>> .entrytext range is [0x20026C, 0x2002D3]

  ld.lld: error: section .text.startup virtual address range overlaps
  with .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header virtual address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata virtual address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

  ld.lld: error: section .text.startup load address range overlaps with
  .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header load address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata load address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

Explicitly pull .text.startup into the .text output section to avoid
this.

[1] https://reviews.llvm.org/D75225

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Reviewed-by: Fangrui Song <maskray@google.com>
---
 arch/x86/boot/setup.ld | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
index 24c95522f231..ed60abcdb089 100644
--- a/arch/x86/boot/setup.ld
+++ b/arch/x86/boot/setup.ld
@@ -20,7 +20,7 @@ SECTIONS
 	.initdata	: { *(.initdata) }
 	__end_init = .;
 
-	.text		: { *(.text) }
+	.text		: { *(.text.startup) *(.text) }
 	.text32		: { *(.text32) }
 
 	. = ALIGN(16);
-- 
2.26.2


^ permalink raw reply related	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-05-21 15:25 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-05-20 22:56 [PATCH 0/1] x86/boot: lld fix Arvind Sankar
2020-05-20 22:56 ` [PATCH 1/1] x86/boot: Add .text.startup to setup.ld Arvind Sankar
2020-05-20 23:33 ` [PATCH 0/1] x86/boot: lld fix Arvind Sankar
2020-05-21  2:12   ` Fangrui Song
2020-05-21 15:20     ` Arvind Sankar
2020-05-21 15:24     ` [PATCH v2] x86/boot: Add .text.startup to setup.ld Arvind Sankar

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