ARM: thumb: Have the machine name indicate operation in thumb mode.

PATCH New Vadim Bendebury 5 participants 15 messages May 13, 2011 – May 26, 2011 1 message not in the archive Arm (32-bit)

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Vadim Bendebury

author

2011-05-13 19:53 UTC #0 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:

localhost ~ # dmesg | grep thumb

[    0.000000] Machine: kaen_thumb

localhost ~ # grep '^Hardware' /proc/cpuinfo
Hardware : kaen_thumb
localhost ~ #

Signed-off-by Vadim Bendebury <[email protected]>

---
 arch/arm/include/asm/mach/arch.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

arch/arm/include/asm/mach/arch.h +7 -1

index bf13b81..c7445a5 100644
@@ -51,12 +51,18 @@ extern struct machine_desc *machine_desc;
  * Set of macros to define architecture features.  This is built into
  * a table by the linker.
  */
+#ifdef CONFIG_THUMB2_KERNEL
+#define NAME_SUFFIX	"_thumb"
+#else
+#define NAME_SUFFIX	""
+#endif
+
 #define MACHINE_START(_type,_name)			\
 static const struct machine_desc __mach_desc_##_type	\
  __used							\
  __attribute__((__section__(".arch.info.init"))) = {	\
 	.nr		= MACH_TYPE_##_type,		\
-	.name		= _name,
+	.name		= _name NAME_SUFFIX,
 
 #define MACHINE_END				\
 };

Signature · 1 line

1.7.3.1

Catalin Marinas

2011-05-14 09:59 UTC #1 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 8 lines · Vadim Bendebury

This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #

Would this break any script parsing this file?

BTW, why do you need it? You could include the .config into the kernel and read it via /proc.

Signature · 1 line

Catalin

Russell King - ARM Linux

2011-05-14 10:02 UTC #2 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 10 lines · Catalin Marinas

Quoted 8 lines · Vadim Bendebury
This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #

Quoted 4 lines

Would this break any script parsing this file?
BTW, why do you need it? You could include the .config into the kernel and read it via /proc.

Whether the kernel is built T2 or ARM doesn't change the userland API either, so there's no real need for userland to know how the kernel was built.

The only thing which is affected by it are kernel modules, but then we have an established way to sort out incompatible kernel modules already.

Dave Martin

2011-05-16 12:16 UTC #3 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 16 lines · Russell King - ARM Linux

Quoted 10 lines · Catalin Marinas
Quoted 8 lines · Vadim Bendebury
This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #
Quoted 4 lines
Would this break any script parsing this file?
BTW, why do you need it? You could include the .config into the kernel and read it via /proc.

Quoted 6 lines

Whether the kernel is built T2 or ARM doesn't change the userland API either, so there's no real need for userland to know how the kernel was built.
The only thing which is affected by it are kernel modules, but then we have an established way to sort out incompatible kernel modules already.

One corollary to that is that _if_ there's any reason why userland needs to know what instruction set the kernel was built with, then we're probably doing something wrong somewhere...

In any case, shoehorning this information into the hardware platform name seems a bit strange since this is really nothing to do with the hardware.

Vadim, can you explain why you think this information is needed? If the need is real, perhaps there's a better way to address it.

Cheers
---Dave

Nicolas Pitre

2011-05-16 14:32 UTC #4 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 28 lines · Dave Martin

Quoted 16 lines · Russell King - ARM Linux
Quoted 10 lines · Catalin Marinas
Quoted 8 lines · Vadim Bendebury
This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #
Quoted 4 lines
Would this break any script parsing this file?
BTW, why do you need it? You could include the .config into the kernel and read it via /proc.
Quoted 6 lines
Whether the kernel is built T2 or ARM doesn't change the userland API either, so there's no real need for userland to know how the kernel was built.
The only thing which is affected by it are kernel modules, but then we have an established way to sort out incompatible kernel modules already.
One corollary to that is that _if_ there's any reason why userland needs to know what instruction set the kernel was built with, then we're probably doing something wrong somewhere...

Quoted 5 lines

In any case, shoehorning this information into the hardware platform name seems a bit strange since this is really nothing to do with the hardware.
Vadim, can you explain why you think this information is needed? If the need is real, perhaps there's a better way to address it.

I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.

Nicolas

Dave Martin

2011-05-16 14:43 UTC #5 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 33 lines · Nicolas Pitre

Quoted 31 lines · Dave Martin
Quoted 16 lines · Russell King - ARM Linux
Quoted 10 lines · Catalin Marinas
Quoted 8 lines · Vadim Bendebury
This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #
Quoted 4 lines
Would this break any script parsing this file?
BTW, why do you need it? You could include the .config into the kernel and read it via /proc.
Quoted 6 lines
Whether the kernel is built T2 or ARM doesn't change the userland API either, so there's no real need for userland to know how the kernel was built.
The only thing which is affected by it are kernel modules, but then we have an established way to sort out incompatible kernel modules already.
One corollary to that is that _if_ there's any reason why userland needs to know what instruction set the kernel was built with, then we're probably doing something wrong somewhere...
In any case, shoehorning this information into the hardware platform name seems a bit strange since this is really nothing to do with the hardware.

Quoted 8 lines

Quoted 2 lines
Vadim, can you explain why you think this information is needed? If the need is real, perhaps there's a better way to address it.
I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.

That seems a reasonable approach to me.

---Dave

Vadim Bendebury (вб)

author

2011-05-18 20:59 UTC #6 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 37 lines · Dave Martin

Quoted 36 lines · Nicolas Pitre
Quoted 33 lines · Dave Martin
Quoted 16 lines · Russell King - ARM Linux
Quoted 10 lines · Catalin Marinas
Quoted 8 lines · Vadim Bendebury
This is a cosmetic change, adding a '_thumb' prefix to the 'Hardware' line in /proc/cpuinfo. Tested as follows:
localhost ~ # dmesg | grep thumb
[ ? ?0.000000] Machine: kaen_thumb localhost ~ # grep '^Hardware' /proc/cpuinfo Hardware ? ? ? ?: kaen_thumb localhost ~ #
Quoted 4 lines
Would this break any script parsing this file?
BTW, why do you need it? You could include the .config into the kernel and read it via /proc.
Quoted 6 lines
Whether the kernel is built T2 or ARM doesn't change the userland API either, so there's no real need for userland to know how the kernel was built.
The only thing which is affected by it are kernel modules, but then we have an established way to sort out incompatible kernel modules already.
One corollary to that is that _if_ there's any reason why userland needs to know what instruction set the kernel was built with, then we're probably doing something wrong somewhere...
In any case, shoehorning this information into the hardware platform name seems a bit strange since this is really nothing to do with the hardware.
Vadim, can you explain why you think this information is needed? ?If the need is real, perhaps there's a better way to address it.

Quoted 8 lines

Quoted 5 lines
I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. ?Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.
That seems a reasonable approach to me.

guys, thank you for your comments. Indeed, this is meant to be just a convenience to allow to quickly tell what kind of kernel a system is running, comes handy when there are many systems around with differently compiled kernels.

So, would it be acceptable if I move this information into the kernel banner (namely, add it to the machine hardware name part of the output included in 'uname -m' and 'uname -a')?

cheers,
/vb

Quoted 2 lines

---Dave

Nicolas Pitre

2011-05-18 22:27 UTC #7 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 11 lines · Vadim Bendebury (??)

Quoted 9 lines · Dave Martin
Quoted 5 lines · Nicolas Pitre
I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. ?Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.
That seems a reasonable approach to me.

Quoted 8 lines

guys, thank you for your comments. Indeed, this is meant to be just a convenience to allow to quickly tell what kind of kernel a system is running, comes handy when there are many systems around with differently compiled kernels.
So, would it be acceptable if I move this information into the kernel banner (namely, add it to the machine hardware name part of the output included in 'uname -m' and 'uname -a')?

Yes, I think that would be the most sensible place. Looking at scripts/mkcompile_h which is used to create include/generated/compile.h, it appears that $CONFIG_FLAGS would be the most appropriate place for this, however it is not currently set up to allow architecture specific flags to be passed in.

Nicolas

Russell King - ARM Linux

2011-05-18 22:33 UTC #8 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 22 lines · Nicolas Pitre

Quoted 11 lines · Vadim Bendebury (??)
Quoted 9 lines · Dave Martin
Quoted 5 lines · Nicolas Pitre
I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. ?Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.
That seems a reasonable approach to me.
Quoted 8 lines
guys, thank you for your comments. Indeed, this is meant to be just a convenience to allow to quickly tell what kind of kernel a system is running, comes handy when there are many systems around with differently compiled kernels.
So, would it be acceptable if I move this information into the kernel banner (namely, add it to the machine hardware name part of the output included in 'uname -m' and 'uname -a')?

Quoted 5 lines

Yes, I think that would be the most sensible place. Looking at scripts/mkcompile_h which is used to create include/generated/compile.h, it appears that $CONFIG_FLAGS would be the most appropriate place for this, however it is not currently set up to allow architecture specific flags to be passed in.

We already have a way of adding stuff for bug tracking purposes. The "Internal error" line is perpended with 'PREEMPT' or 'SMP' depending on what build options were enabled. We just need to do the same with T2. IOW, something like this:

arch/arm/kernel/traps.c +7 -2

index 3b54ad1..78d7714 100644
@@ -225,6 +225,11 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
 #else
 #define S_SMP ""
 #endif
+#ifdef CONFIG_THUMB2_KERNEL
+#define S_ISA " T2"
+#else
+#define S_ISA " ARM"
+#endif
 
 static int __die(const char *str, int err, struct thread_info *thread, struct pt_regs *regs)
 {

@@ -232,8 +237,8 @@ static int __die(const char *str, int err, struct thread_info *thread, struct pt
 	static int die_counter;
 	int ret;
 
-	printk(KERN_EMERG "Internal error: %s: %x [#%d]" S_PREEMPT S_SMP "\n",
-	       str, err, ++die_counter);
+	printk(KERN_EMERG "Internal error: %s: %x [#%d]" S_PREEMPT S_SMP
+	       S_ISA "\n", str, err, ++die_counter);
 	sysfs_printk_last_file();
 
 	/* trap and error numbers are mostly meaningless on ARM */

Nicolas Pitre

2011-05-18 22:49 UTC #9 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 29 lines · Russell King - ARM Linux

Quoted 22 lines · Nicolas Pitre
Quoted 11 lines · Vadim Bendebury (??)
Quoted 9 lines · Dave Martin
Quoted 5 lines · Nicolas Pitre
I think this can be useful to know how the kernel was compiled for bug tracking purposes, just like we record the Git commit ID of the checked out source tree, the gcc version, the build date, etc. ?Which pretty much indicates that the thumbness of the kernel should probably be stored in the kernel banner not the platform name.
That seems a reasonable approach to me.
Quoted 8 lines
guys, thank you for your comments. Indeed, this is meant to be just a convenience to allow to quickly tell what kind of kernel a system is running, comes handy when there are many systems around with differently compiled kernels.
So, would it be acceptable if I move this information into the kernel banner (namely, add it to the machine hardware name part of the output included in 'uname -m' and 'uname -a')?
Quoted 5 lines
Yes, I think that would be the most sensible place. Looking at scripts/mkcompile_h which is used to create include/generated/compile.h, it appears that $CONFIG_FLAGS would be the most appropriate place for this, however it is not currently set up to allow architecture specific flags to be passed in.

Quoted 4 lines

We already have a way of adding stuff for bug tracking purposes. The "Internal error" line is perpended with 'PREEMPT' or 'SMP' depending on what build options were enabled. We just need to do the same with T2. IOW, something like this:

[...]

This is indeed useful if the kernel oopses. However this doesn't help for those cases where the kernel doesn't crash but still exhibits unexpected behaviors. Having the thumbness of the kernel also displayed in dmesg and uname -a would also be good to have.

Nicolas

Russell King - ARM Linux

2011-05-18 22:57 UTC #10 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 11 lines · Nicolas Pitre

Quoted 4 lines · Russell King - ARM Linux
We already have a way of adding stuff for bug tracking purposes. The "Internal error" line is perpended with 'PREEMPT' or 'SMP' depending on what build options were enabled. We just need to do the same with T2. IOW, something like this:
[...]
This is indeed useful if the kernel oopses. However this doesn't help for those cases where the kernel doesn't crash but still exhibits unexpected behaviors. Having the thumbness of the kernel also displayed in dmesg and uname -a would also be good to have.

In which case I think we'll have to talk to kbuild people to get mkcompile_h modified. Also maybe asking what other architectures do for this kind of problem may be a good idea - especially before we start abusing and hacking stuff like the hardware name.

A message that is not in the archive (sent off-list or not yet received): [email protected]

Russell King - ARM Linux

2011-05-26 13:01 UTC #12 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 9 lines · Vadim Bendebury (??)

Quoted 4 lines · Russell King - ARM Linux
In which case I think we'll have to talk to kbuild people to get mkcompile_h modified. Also maybe asking what other architectures do for this kind of problem may be a good idea - especially before we start abusing and hacking stuff like the hardware name.
So, what would be an equivalent in other architectures to ask about - it seems that the ability to run in Thumb/ARM mode is fairly unique for ARM.

What about 32-bit vs 64-bit x86 ?

Quoted 7 lines

Consulting /boot/config file is not reliable: in my own setup I can netboot either thumb or ARM kernel without changing the root file system contents. I agree though that changing the hardware name is not the best way to do this either.
I could look into adding 'thumb' to any element of the uname output, or as a watered down version - just add a line to dmesg output?

The thing that I worry about is that userspace will start using this information inappropriately. Whether the kernel is built as T2 or ARM is really only a matter for the kernel itself (and people debugging the kernel), rather than random userspace programs.

Maybe a way forward would be to produce a patch for mkcompile_h, post it to here, kbuild people and LKML and see what response is forthcoming.

Dave Martin

2011-05-26 13:56 UTC #13 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 8 lines · Russell King - ARM Linux

Quoted 7 lines · Vadim Bendebury (??)
Quoted 4 lines · Russell King - ARM Linux
In which case I think we'll have to talk to kbuild people to get mkcompile_h modified. Also maybe asking what other architectures do for this kind of problem may be a good idea - especially before we start abusing and hacking stuff like the hardware name.

Quoted 4 lines

Quoted 2 lines
So, what would be an equivalent in other architectures to ask about - it seems that the ability to run in Thumb/ARM mode is fairly unique for ARM.
What about 32-bit vs 64-bit x86 ?

Thumb seems different because is is irrelevant to the kernel/user ABI (or, if it's not irrelevant, we have a bug somewhere...)

Documenting what ISA the kernel was built with is therefore similar to documenting what optimisation options were used -- i.e., it's interesting and occasionally useful for humans, but not something software should normally be querying or care about in any way.

Quoted 5 lines

Quoted 5 lines
Consulting /boot/config file is not reliable: in my own setup I can netboot either thumb or ARM kernel without changing the root file system contents. I agree though that changing the hardware name is not the best way to do this either.

Quoted 7 lines

Quoted 2 lines
I could look into adding 'thumb' to any element of the uname output, or as a watered down version - just add a line to dmesg output?
The thing that I worry about is that userspace will start using this information inappropriately. Whether the kernel is built as T2 or ARM is really only a matter for the kernel itself (and people debugging the kernel), rather than random userspace programs.

Agreed

Quoted 8 lines

Maybe a way forward would be to produce a patch for mkcompile_h, post it to here, kbuild people and LKML and see what response is forthcoming.
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Russell King - ARM Linux

2011-05-26 13:59 UTC #14 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

Quoted 14 lines · Dave Martin

Quoted 8 lines · Russell King - ARM Linux
Quoted 7 lines · Vadim Bendebury (??)
Quoted 4 lines · Russell King - ARM Linux
In which case I think we'll have to talk to kbuild people to get mkcompile_h modified. Also maybe asking what other architectures do for this kind of problem may be a good idea - especially before we start abusing and hacking stuff like the hardware name.
Quoted 4 lines
Quoted 2 lines
So, what would be an equivalent in other architectures to ask about - it seems that the ability to run in Thumb/ARM mode is fairly unique for ARM.
What about 32-bit vs 64-bit x86 ?

Quoted 7 lines

Thumb seems different because is is irrelevant to the kernel/user ABI (or, if it's not irrelevant, we have a bug somewhere...)
Documenting what ISA the kernel was built with is therefore similar to documenting what optimisation options were used -- i.e., it's interesting and occasionally useful for humans, but not something software should normally be querying or care about in any way.

In which case its a bit like exposing whether the kernel was built with or without frame pointers, or which -O level, which compiler flags, etc.

I think its best therefore that it remains in the kernel config along with all the other 'optimisation' settings.

We don't even need to print it in the oops report because that already tells us what ISA we were executing as - and from that and the Code: line we can imply the kernel build ISA.

Dave Martin

2011-05-19 08:36 UTC #15 lore raw

PATCH 1/1 ARM: thumb: Have the machine name indicate operation in thumb mode.

In reply to Russell King - ARM Linux

On Wed, May 18, 2011 at 11:33:19PM +0100, Russell King - ARM Linux wrote:

[...]

Quoted 10 lines

We already have a way of adding stuff for bug tracking purposes. The "Internal error" line is perpended with 'PREEMPT' or 'SMP' depending on what build options were enabled. We just need to do the same with T2. IOW, something like this:
arch/arm/kernel/traps.c +0 -0
index 3b54ad1..78d7714 100644

arch/arm/kernel/traps.c void show_stack(struct task_struct *tsk, unsigned long *sp) · line 229

Quoted 5 lines

arch/arm/kernel/traps.c +2 -0

@@ -225,6 +225,11 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
 #else
 #define S_SMP ""
 #endif
+#ifdef CONFIG_THUMB2_KERNEL
+#define S_ISA " T2"

Just for consistency, can I suggest that if this is implemented, we make the string " thumb2"? (upper case optional) This matches what we now put in MODULE_ARCH_VERMAGIC, as well as being closer to the CONFIG_ name.

Cheers
---Dave