x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

[PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Vincent Mailhol 2 years, 9 months ago

Following [1], the macro COMPILE_OFFSETS becomes unused:
  $ make W=2 arch/x86/kernel/asm-offsets.o
  <...>
  arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
  <...>

Remove COMPILE_OFFSETS macro.

[1] commit debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
    Link: https://git.kernel.org/torvalds/linux/c/debc5a1ec0d1

Fixes: debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
 arch/x86/kernel/asm-offsets.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 437308004ef2..cf2e02bafbef 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -4,7 +4,6 @@
  * This code generates raw asm output which is post-processed to extract
  * and format the required data.
  */
-#define COMPILE_OFFSETS
 
 #include <linux/crypto.h>
 #include <linux/sched.h>
-- 
2.37.4

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Kirill A . Shutemov 2 years, 9 months ago

On Sun, Nov 27, 2022 at 03:23:35PM +0900, Vincent Mailhol wrote:
> Following [1], the macro COMPILE_OFFSETS becomes unused:

Really? I see #ifdef COMPILE_OFFSETS in ftrace.h. Hm?

Have you tested your patch with CONFIG_FTRACE_SYSCALLS=y and
CONFIG_IA32_EMULATION=y?

>   $ make W=2 arch/x86/kernel/asm-offsets.o
>   <...>
>   arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
>   <...>
> 
> Remove COMPILE_OFFSETS macro.
> 
> [1] commit debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
>     Link: https://git.kernel.org/torvalds/linux/c/debc5a1ec0d1
> 
> Fixes: debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> ---
>  arch/x86/kernel/asm-offsets.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
> index 437308004ef2..cf2e02bafbef 100644
> --- a/arch/x86/kernel/asm-offsets.c
> +++ b/arch/x86/kernel/asm-offsets.c
> @@ -4,7 +4,6 @@
>   * This code generates raw asm output which is post-processed to extract
>   * and format the required data.
>   */
> -#define COMPILE_OFFSETS
>  
>  #include <linux/crypto.h>
>  #include <linux/sched.h>
> -- 
> 2.37.4
> 

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Vincent Mailhol 2 years, 9 months ago

On Mon, 28 Nov 2022 12:15:06 +0300, Kirill A. Shutemov wrote:
> On Sun, Nov 27, 2022 at 03:23:35PM +0900, Vincent Mailhol wrote:
> > Following [1], the macro COMPILE_OFFSETS becomes unused:
> 
> Really? I see #ifdef COMPILE_OFFSETS in ftrace.h. Hm?
> 
> Have you tested your patch with CONFIG_FTRACE_SYSCALLS=y and
> CONFIG_IA32_EMULATION=y?

Even if I activate those two configurations, the compiler still
tells me it is unused:

  $ grep -E "CONFIG_FTRACE_SYSCALLS|CONFIG_IA32_EMULATION" .config
  CONFIG_IA32_EMULATION=y
  CONFIG_FTRACE_SYSCALLS=y

  $ make W=2 arch/x86/kernel/asm-offsets.o
  <...>
  arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
  <...>

> >   $ make W=2 arch/x86/kernel/asm-offsets.o
> >   <...>
> >   arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
> >   <...>
> > 
> > Remove COMPILE_OFFSETS macro.
> > 
> > [1] commit debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
> >     Link: https://git.kernel.org/torvalds/linux/c/debc5a1ec0d1
> > 
> > Fixes: debc5a1ec0d1 ("KVM: x86: use a separate asm-offsets.c file")
> > Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > ---
> >  arch/x86/kernel/asm-offsets.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
> > index 437308004ef2..cf2e02bafbef 100644
> > --- a/arch/x86/kernel/asm-offsets.c
> > +++ b/arch/x86/kernel/asm-offsets.c
> > @@ -4,7 +4,6 @@
> >   * This code generates raw asm output which is post-processed to extract
> >   * and format the required data.
> >   */
> > -#define COMPILE_OFFSETS
> >  
> >  #include <linux/crypto.h>
> >  #include <linux/sched.h>

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by kirill.shutemov@linux.intel.com 2 years, 9 months ago

On Mon, Nov 28, 2022 at 07:11:17PM +0900, Vincent Mailhol wrote:
> On Mon, 28 Nov 2022 12:15:06 +0300, Kirill A. Shutemov wrote:
> > On Sun, Nov 27, 2022 at 03:23:35PM +0900, Vincent Mailhol wrote:
> > > Following [1], the macro COMPILE_OFFSETS becomes unused:
> > 
> > Really? I see #ifdef COMPILE_OFFSETS in ftrace.h. Hm?
> > 
> > Have you tested your patch with CONFIG_FTRACE_SYSCALLS=y and
> > CONFIG_IA32_EMULATION=y?
> 
> Even if I activate those two configurations, the compiler still
> tells me it is unused:
> 
>   $ grep -E "CONFIG_FTRACE_SYSCALLS|CONFIG_IA32_EMULATION" .config
>   CONFIG_IA32_EMULATION=y
>   CONFIG_FTRACE_SYSCALLS=y
> 
>   $ make W=2 arch/x86/kernel/asm-offsets.o
>   <...>
>   arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
>   <...>

If you are sure <asm/ftrace.h> is never included from asm-offsets.c,
remove #ifndef COMPILE_OFFSETS too.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Vincent MAILHOL 2 years, 9 months ago

On Mon. 28 Nov. 2022 at 20:11, <kirill.shutemov@linux.intel.com> wrote:
> On Mon, Nov 28, 2022 at 07:11:17PM +0900, Vincent Mailhol wrote:
> > On Mon, 28 Nov 2022 12:15:06 +0300, Kirill A. Shutemov wrote:
> > > On Sun, Nov 27, 2022 at 03:23:35PM +0900, Vincent Mailhol wrote:
> > > > Following [1], the macro COMPILE_OFFSETS becomes unused:
> > >
> > > Really? I see #ifdef COMPILE_OFFSETS in ftrace.h. Hm?
> > >
> > > Have you tested your patch with CONFIG_FTRACE_SYSCALLS=y and
> > > CONFIG_IA32_EMULATION=y?
> >
> > Even if I activate those two configurations, the compiler still
> > tells me it is unused:
> >
> >   $ grep -E "CONFIG_FTRACE_SYSCALLS|CONFIG_IA32_EMULATION" .config
> >   CONFIG_IA32_EMULATION=y
> >   CONFIG_FTRACE_SYSCALLS=y
> >
> >   $ make W=2 arch/x86/kernel/asm-offsets.o
> >   <...>
> >   arch/x86/kernel/asm-offsets.c:7: warning: macro "COMPILE_OFFSETS" is not used [-Wunused-macros]
> >   <...>
>
> If you are sure <asm/ftrace.h> is never included from asm-offsets.c,
> remove #ifndef COMPILE_OFFSETS too.

It is never included from asm-offsets.c but it is still used by
kvm-asm-offsets.c:
https://elixir.bootlin.com/linux/v6.1-rc7/source/arch/x86/kvm/kvm-asm-offsets.c#L7

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Steven Rostedt 2 years, 9 months ago

On Mon, 28 Nov 2022 20:30:35 +0900
Vincent MAILHOL <mailhol.vincent@wanadoo.fr> wrote:

> > If you are sure <asm/ftrace.h> is never included from asm-offsets.c,
> > remove #ifndef COMPILE_OFFSETS too.  
> 
> It is never included from asm-offsets.c but it is still used by
> kvm-asm-offsets.c:
> https://elixir.bootlin.com/linux/v6.1-rc7/source/arch/x86/kvm/kvm-asm-offsets.c#L7

IIRC, the reason for adding that was because that logic was screwing up
asm-offsets.c. I'm not sure it screws up kvm-asm-offsets.c though.

This is one of those cases I wish I commented that code better :-/

-- Steve

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Paolo Bonzini 2 years, 9 months ago

On 11/28/22 18:45, Steven Rostedt wrote:
> 
>>> If you are sure <asm/ftrace.h> is never included from asm-offsets.c,
>>> remove #ifndef COMPILE_OFFSETS too.
>> It is never included from asm-offsets.c but it is still used by
>> kvm-asm-offsets.c:
>> https://elixir.bootlin.com/linux/v6.1-rc7/source/arch/x86/kvm/kvm-asm-offsets.c#L7
> IIRC, the reason for adding that was because that logic was screwing up
> asm-offsets.c. I'm not sure it screws up kvm-asm-offsets.c though.
> 
> This is one of those cases I wish I commented that code better :-/

I don't think KVM includes linux/ftrace.h or asm/ftrace.h at all.

Paolo

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Sean Christopherson 2 years, 9 months ago

On Mon, Nov 28, 2022, Paolo Bonzini wrote:
> On 11/28/22 18:45, Steven Rostedt wrote:
> > 
> > > > If you are sure <asm/ftrace.h> is never included from asm-offsets.c,
> > > > remove #ifndef COMPILE_OFFSETS too.
> > > It is never included from asm-offsets.c but it is still used by
> > > kvm-asm-offsets.c:
> > > https://elixir.bootlin.com/linux/v6.1-rc7/source/arch/x86/kvm/kvm-asm-offsets.c#L7
> > IIRC, the reason for adding that was because that logic was screwing up
> > asm-offsets.c. I'm not sure it screws up kvm-asm-offsets.c though.
> > 
> > This is one of those cases I wish I commented that code better :-/
> 
> I don't think KVM includes linux/ftrace.h or asm/ftrace.h at all.

From include/linux/kvm_host.h

  #include <linux/ftrace.h>

Even if that didn't exist, saying that XYZ never includes a header is a dangerous
business, it's all too easy to indirectly include headers in the kernel, now or
in the future.

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Steven Rostedt 2 years, 9 months ago

On Mon, 28 Nov 2022 18:06:18 +0000
Sean Christopherson <seanjc@google.com> wrote:

> > > IIRC, the reason for adding that was because that logic was screwing up
> > > asm-offsets.c. I'm not sure it screws up kvm-asm-offsets.c though.
> > > 
> > > This is one of those cases I wish I commented that code better :-/  
> > 
> > I don't think KVM includes linux/ftrace.h or asm/ftrace.h at all.  
> 
> >From include/linux/kvm_host.h  
> 
>   #include <linux/ftrace.h>
> 
> Even if that didn't exist, saying that XYZ never includes a header is a dangerous
> business, it's all too easy to indirectly include headers in the kernel, now or
> in the future.

But going back to the original intent of COMPILE_OFFSETS. I believe it was
because some code that did not work with the auto generation of compiler
offsets and was a way to hide them.

I do not know if it is still an issue or not today.

-- Steve

Re: [PATCH] x86/asm: Remove unused COMPILE_OFFSETS macro from asm-offsets.c

Posted by Vincent MAILHOL 2 years, 9 months ago

On Tue. 29 Nov. 2022 at 04:10, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 28 Nov 2022 18:06:18 +0000
> Sean Christopherson <seanjc@google.com> wrote:
>
> > > > IIRC, the reason for adding that was because that logic was screwing up
> > > > asm-offsets.c. I'm not sure it screws up kvm-asm-offsets.c though.
> > > >
> > > > This is one of those cases I wish I commented that code better :-/
> > >
> > > I don't think KVM includes linux/ftrace.h or asm/ftrace.h at all.
> >
> > >From include/linux/kvm_host.h
> >
> >   #include <linux/ftrace.h>
> >
> > Even if that didn't exist, saying that XYZ never includes a header is a dangerous
> > business, it's all too easy to indirectly include headers in the kernel, now or
> > in the future.

ACK. This is why I relied on the compiler's -Wunused-macros to assert
that COMPILE_OFFSETS can be removed from asm-offsets.c but not from
kvm-asm-offsets.c.
I also asserted that it is
https://git.kernel.org/torvalds/linux/c/debc5a1ec0d1 which removed the
dependency.

> But going back to the original intent of COMPILE_OFFSETS. I believe it was
> because some code that did not work with the auto generation of compiler
> offsets and was a way to hide them.
>
> I do not know if it is still an issue or not today.

This I do not know. I only have the confidence to remove
COMPILE_OFFSETS from asm-offsets.c. Nothing more.