[PATCH] x86_64: ifdef out struct thread_struct::ip

[PATCH] x86_64: ifdef out struct thread_struct::ip

[Alexey Dobriyan]

struct thread_struct::ip isn't used on x86_64, struct pt_regs::ip is used
instead.

kgdb should be reading 0 always, but I can't check it.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
 arch/x86/include/asm/processor.h |    2 ++
 arch/x86/kernel/kgdb.c           |    2 +-
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a6732ff..a9ba743 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -427,7 +427,9 @@ struct thread_struct {
 	unsigned short		fsindex;
 	unsigned short		gsindex;
 #endif
+#ifdef CONFIG_X86_32
 	unsigned long		ip;
+#endif
 #ifdef CONFIG_X86_64
 	unsigned long		fs;
 #endif
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index eedfaeb..d07706f 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -141,7 +141,7 @@ void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
 	gdb_regs32[GDB_PS]	= *(unsigned long *)(p->thread.sp + 8);
 	gdb_regs32[GDB_CS]	= __KERNEL_CS;
 	gdb_regs32[GDB_SS]	= __KERNEL_DS;
-	gdb_regs[GDB_PC]	= p->thread.ip;
+	gdb_regs[GDB_PC]	= 0;
 	gdb_regs[GDB_R8]	= 0;
 	gdb_regs[GDB_R9]	= 0;
 	gdb_regs[GDB_R10]	= 0;

[tip:x86/asm] x86, 64-bit: ifdef out struct thread_struct::ip

[tip-bot for Alexey Dobriyan]

Commit-ID:  0c23590f00f85467b318ad0c20c36796a5bd4c60
Gitweb:     http://git.kernel.org/tip/0c23590f00f85467b318ad0c20c36796a5bd4c60
Author:     Alexey Dobriyan <adobriyan@gmail.com>
AuthorDate: Mon, 4 May 2009 03:30:15 +0400
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 11 May 2009 16:23:54 +0200

x86, 64-bit: ifdef out struct thread_struct::ip

struct thread_struct::ip isn't used on x86_64, struct pt_regs::ip is used
instead.

kgdb should be reading 0 always, but I can't check it.

[ Impact: (potentially) reduce thread_struct size on 64-bit ]

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: containers@lists.linux-foundation.org
LKML-Reference: <20090503233015.GJ16631@x200.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 arch/x86/include/asm/processor.h |    2 ++
 arch/x86/kernel/kgdb.c           |    2 +-
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a6732ff..a9ba743 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -427,7 +427,9 @@ struct thread_struct {
 	unsigned short		fsindex;
 	unsigned short		gsindex;
 #endif
+#ifdef CONFIG_X86_32
 	unsigned long		ip;
+#endif
 #ifdef CONFIG_X86_64
 	unsigned long		fs;
 #endif
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index eedfaeb..d07706f 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -141,7 +141,7 @@ void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
 	gdb_regs32[GDB_PS]	= *(unsigned long *)(p->thread.sp + 8);
 	gdb_regs32[GDB_CS]	= __KERNEL_CS;
 	gdb_regs32[GDB_SS]	= __KERNEL_DS;
-	gdb_regs[GDB_PC]	= p->thread.ip;
+	gdb_regs[GDB_PC]	= 0;
 	gdb_regs[GDB_R8]	= 0;
 	gdb_regs[GDB_R9]	= 0;
 	gdb_regs[GDB_R10]	= 0;

Re: [tip:x86/asm] x86, 64-bit: ifdef out struct thread_struct::ip

[Christoph Hellwig]

On Mon, May 11, 2009 at 03:09:40PM +0000, tip-bot for Alexey Dobriyan wrote:
> +#ifdef CONFIG_X86_32
>  	unsigned long		ip;
> +#endif
>  #ifdef CONFIG_X86_64
>  	unsigned long		fs;
>  #endif

What happened to the good old concept of #if #else #endif?

Re: [tip:x86/asm] x86, 64-bit: ifdef out struct thread_struct::ip

[Alexey Dobriyan]

On Mon, May 11, 2009 at 8:03 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, May 11, 2009 at 03:09:40PM +0000, tip-bot for Alexey Dobriyan wrote:
>> +#ifdef CONFIG_X86_32
>>       unsigned long           ip;
>> +#endif
>>  #ifdef CONFIG_X86_64
>>       unsigned long           fs;
>>  #endif
>
> What happened to the good old concept of #if #else #endif?

#else suggests alternative which is not the case.
->ip and ->fs can be in different parts of thread_struct.

Re: [tip:x86/asm] x86, 64-bit: ifdef out struct thread_struct::ip

[Robert P. J. Day]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1610 bytes --]

On Mon, 11 May 2009, Alexey Dobriyan wrote:

> On Mon, May 11, 2009 at 8:03 PM, Christoph Hellwig <hch@infradead.org> wrote:
> > On Mon, May 11, 2009 at 03:09:40PM +0000, tip-bot for Alexey Dobriyan wrote:
> >> +#ifdef CONFIG_X86_32
> >>       unsigned long           ip;
> >> +#endif
> >>  #ifdef CONFIG_X86_64
> >>       unsigned long           fs;
> >>  #endif
> >
> > What happened to the good old concept of #if #else #endif?
>
> #else suggests alternative which is not the case.
> ->ip and ->fs can be in different parts of thread_struct.

  the arch/x86/Kconfig file certainly suggests that those are
mutually-exclusive alternatives:

...
# Select 32 or 64 bit
config 64BIT
        bool "64-bit kernel" if ARCH = "x86"
        default ARCH = "x86_64"
        ---help---
          Say yes to build a 64-bit kernel - formerly known as x86_64
          Say no to build a 32-bit kernel - formerly known as i386

config X86_32
        def_bool !64BIT

config X86_64
        def_bool 64BIT
...

unless there's something weird going on underneath.

rday
--

========================================================================
Robert P. J. Day                               Waterloo, Ontario, CANADA

        Linux Consulting, Training and Annoying Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Linked In:                             http://www.linkedin.com/in/rpjday
Twitter:                                       http://twitter.com/rpjday
========================================================================

Re: [tip:x86/asm] x86, 64-bit: ifdef out struct thread_struct::ip

[Ingo Molnar]

* Alexey Dobriyan <adobriyan@gmail.com> wrote:

> On Mon, May 11, 2009 at 8:03 PM, Christoph Hellwig <hch@infradead.org> wrote:
> > On Mon, May 11, 2009 at 03:09:40PM +0000, tip-bot for Alexey Dobriyan wrote:
> >> +#ifdef CONFIG_X86_32
> >>       unsigned long           ip;
> >> +#endif
> >>  #ifdef CONFIG_X86_64
> >>       unsigned long           fs;
> >>  #endif
> >
> > What happened to the good old concept of #if #else #endif?
> 
> #else suggests alternative which is not the case.
> ->ip and ->fs can be in different parts of thread_struct.

Yes, it's cleaner to have them separate. #if / #else / #endif would 
be shorter by one line, and it would be thicker by a big confusion 
factor: "why is fs the alternative on 64-bit of 32-bit's ip??"

They could also move apart later on, if structure packing 
constraints call for it.

	Ingo