In the kernel image vmlinux.lds.S linker scripts the .altinstructions
and __bug_table sections are 32- or 64-bit aligned because they hold 32-
and/or 64-bit values.
But for modules the module.lds.S linker script doesn't define a default
alignment yet, so the linker chooses the default byte-alignment, which
then leads to unnecessary unaligned memory accesses at runtime.
This patch adds the missing alignments.
Signed-off-by: Helge Deller <[email protected]>
---
scripts/module.lds.S | 2 ++
1 file changed, 2 insertions(+)
diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 1d0e1e4dc3d2..3a3aa2354ed8 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -27,6 +27,8 @@ SECTIONS {
.ctors 0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) }
.init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
+ .altinstructions 0 : ALIGN(8) { KEEP(*(.altinstructions)) }
+ __bug_table 0 : ALIGN(8) { KEEP(*(__bug_table)) }
__jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
__patchable_function_entries : { *(__patchable_function_entries) }
--
2.35.3
The scripts/module.lds.S and scripts/modules-check.sh files
should be maintained by the "MODULE SUPPORT" maintainers.
Signed-off-by: Helge Deller <[email protected]>
---
MAINTAINERS | 1 +
1 file changed, 1 insertion(+)
diff --git a/MAINTAINERS b/MAINTAINERS
index fe5daf141501..6073fc7c0fa4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13471,6 +13471,7 @@ S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git modules-next
F: include/linux/module.h
F: kernel/module/
+F: scripts/module*
MONOLITHIC POWER SYSTEM PMIC DRIVER
M: Saravanan Sekar <[email protected]>
--
2.35.3
On Mon, Jun 27, 2022 at 09:05:50PM +0200, Helge Deller wrote:
> In the kernel image vmlinux.lds.S linker scripts the .altinstructions
> and __bug_table sections are 32- or 64-bit aligned because they hold 32-
> and/or 64-bit values.
>
> But for modules the module.lds.S linker script doesn't define a default
> alignment yet, so the linker chooses the default byte-alignment, which
> then leads to unnecessary unaligned memory accesses at runtime.
>
> This patch adds the missing alignments.
>
> Signed-off-by: Helge Deller <[email protected]>
Good catch but does this fix a real world issue? When are
altinstructions used for modules? When are alternatives used
for modules?
How did you notice this issue?
This information should go into the commit log.
Luis
> ---
> scripts/module.lds.S | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 1d0e1e4dc3d2..3a3aa2354ed8 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -27,6 +27,8 @@ SECTIONS {
> .ctors 0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) }
> .init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
>
> + .altinstructions 0 : ALIGN(8) { KEEP(*(.altinstructions)) }
> + __bug_table 0 : ALIGN(8) { KEEP(*(__bug_table)) }
> __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
>
> __patchable_function_entries : { *(__patchable_function_entries) }
> --
> 2.35.3
>
On 7/1/22 20:02, Luis Chamberlain wrote:
> On Mon, Jun 27, 2022 at 09:05:50PM +0200, Helge Deller wrote:
>> In the kernel image vmlinux.lds.S linker scripts the .altinstructions
>> and __bug_table sections are 32- or 64-bit aligned because they hold 32-
>> and/or 64-bit values.
>>
>> But for modules the module.lds.S linker script doesn't define a default
>> alignment yet, so the linker chooses the default byte-alignment, which
>> then leads to unnecessary unaligned memory accesses at runtime.
>>
>> This patch adds the missing alignments.
>>
>> Signed-off-by: Helge Deller <[email protected]>
>
> Good catch but does this fix a real world issue? When are
> altinstructions used for modules? When are alternatives used
> for modules?
>
> How did you notice this issue?
You are right - usually this is unnoticed, because either the
hardware (on x86 cpus) or by exception handlers (e.g. on hppa
or sparc) fix up such unaligned accesses at runtime.
I noticed that, because on hppa the 32-bit unalignment handler
was broken due a bad commit, and as such wrong values were
returned on unaligned accesses, which then led to other bugs.
For hppa I fixed it with this commit:
https://patchwork.kernel.org/project/linux-parisc/patch/[email protected]/
This happened when loading the mptbase kernel module:
https://lore.kernel.org/all/[email protected]/T/#mab602dfa32be5e229d5e192ab012af196d04d75d
The summary why it went wrong is at the end of that thread.
On hppa we replace "sync" and some other instructions in kernel
and modules - depending on the CPU type (detected at runtime), or
on the environment (e.g. when running in qemu).
IMHO this really should be fixed, esp. since the fix is trivial.
> This information should go into the commit log.
Sure, I'll resend with updated info.
Thanks!
Helge
>> scripts/module.lds.S | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
>> index 1d0e1e4dc3d2..3a3aa2354ed8 100644
>> --- a/scripts/module.lds.S
>> +++ b/scripts/module.lds.S
>> @@ -27,6 +27,8 @@ SECTIONS {
>> .ctors 0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) }
>> .init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
>>
>> + .altinstructions 0 : ALIGN(8) { KEEP(*(.altinstructions)) }
>> + __bug_table 0 : ALIGN(8) { KEEP(*(__bug_table)) }
>> __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
>>
>> __patchable_function_entries : { *(__patchable_function_entries) }
>> --
>> 2.35.3
>>
On Mon, Jun 27, 2022 at 09:05:51PM +0200, Helge Deller wrote:
> The scripts/module.lds.S and scripts/modules-check.sh files
> should be maintained by the "MODULE SUPPORT" maintainers.
>
> Signed-off-by: Helge Deller <[email protected]>
Thanks! Queued onto modules-next.
Luis