[PATCH] Documentation: x86: Fix obsolete name of page fault handler

[PATCH] Documentation: x86: Fix obsolete name of page fault handler

[Chin En Lin]

Since commit 91eeafea1e4b ("x86/entry: Switch page fault
exception to IDTENTRY_RAW"), the function name of page
fault handler is out of date. This patch change
do_page_fault() to exc_page_fault().

Signed-off-by: Chin En Lin <shiyn.lin@gmail.com>
---
 Documentation/x86/exception-tables.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/x86/exception-tables.rst b/Documentation/x86/exception-tables.rst
index de58110c5ffd..0140a06b2705 100644
--- a/Documentation/x86/exception-tables.rst
+++ b/Documentation/x86/exception-tables.rst
@@ -32,14 +32,14 @@ Whenever the kernel tries to access an address that is currently not
 accessible, the CPU generates a page fault exception and calls the
 page fault handler::
 
-  void do_page_fault(struct pt_regs *regs, unsigned long error_code)
+  void exc_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 in arch/x86/mm/fault.c. The parameters on the stack are set up by
 the low level assembly glue in arch/x86/entry/entry_32.S. The parameter
 regs is a pointer to the saved registers on the stack, error_code
 contains a reason code for the exception.
 
-do_page_fault first obtains the unaccessible address from the CPU
+exc_page_fault first obtains the unaccessible address from the CPU
 control register CR2. If the address is within the virtual address
 space of the process, the fault probably occurred, because the page
 was not swapped in, write protected or something similar. However,
@@ -281,12 +281,12 @@ vma occurs?
 
     > c017e7a5 <do_con_write+e1> movb   (%ebx),%dl
 #. MMU generates exception
-#. CPU calls do_page_fault
+#. CPU calls exc_page_fault
 #. do page fault calls search_exception_table (regs->eip == c017e7a5);
 #. search_exception_table looks up the address c017e7a5 in the
    exception table (i.e. the contents of the ELF section __ex_table)
    and returns the address of the associated fault handle code c0199ff5.
-#. do_page_fault modifies its own return address to point to the fault
+#. exc_page_fault modifies its own return address to point to the fault
    handle code and returns.
 #. execution continues in the fault handling code.
 #. a) EAX becomes -EFAULT (== -14)
-- 
2.25.1

Re: [PATCH] Documentation: x86: Fix obsolete name of page fault handler

[Borislav Petkov]

On Mon, Mar 14, 2022 at 11:59:01PM +0800, Chin En Lin wrote:
> Since commit 91eeafea1e4b ("x86/entry: Switch page fault
> exception to IDTENTRY_RAW"), the function name of page
> fault handler is out of date. This patch change
> do_page_fault() to exc_page_fault().

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

Also, do not talk about what your patch does - that should hopefully be
visible in the diff itself. Rather, talk about *why* you're doing what
you're doing.

> Signed-off-by: Chin En Lin <shiyn.lin@gmail.com>
> ---
>  Documentation/x86/exception-tables.rst | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/x86/exception-tables.rst b/Documentation/x86/exception-tables.rst
> index de58110c5ffd..0140a06b2705 100644
> --- a/Documentation/x86/exception-tables.rst
> +++ b/Documentation/x86/exception-tables.rst
> @@ -32,14 +32,14 @@ Whenever the kernel tries to access an address that is currently not
>  accessible, the CPU generates a page fault exception and calls the
>  page fault handler::
>  
> -  void do_page_fault(struct pt_regs *regs, unsigned long error_code)
> +  void exc_page_fault(struct pt_regs *regs, unsigned long error_code)
>  
>  in arch/x86/mm/fault.c. The parameters on the stack are set up by
>  the low level assembly glue in arch/x86/entry/entry_32.S. The parameter
>  regs is a pointer to the saved registers on the stack, error_code
>  contains a reason code for the exception.
>  
> -do_page_fault first obtains the unaccessible address from the CPU
> +exc_page_fault first obtains the unaccessible address from the CPU

Unknown word [unaccessible] in Documentation.
Suggestions: ['inaccessible', 'accessible', 'accessibly']

Also, put "()" after the function name:

"exc_page_fault() first obtains..."

>  control register CR2. If the address is within the virtual address
>  space of the process, the fault probably occurred, because the page
>  was not swapped in, write protected or something similar. However,
> @@ -281,12 +281,12 @@ vma occurs?
>  
>      > c017e7a5 <do_con_write+e1> movb   (%ebx),%dl
>  #. MMU generates exception
> -#. CPU calls do_page_fault
> +#. CPU calls exc_page_fault
>  #. do page fault calls search_exception_table (regs->eip == c017e7a5);

That is not really true anymore - look at the code and see which
function calls fixup_exception() now and try to fix that too pls.

>  #. search_exception_table looks up the address c017e7a5 in the
>     exception table (i.e. the contents of the ELF section __ex_table)
>     and returns the address of the associated fault handle code c0199ff5.
> -#. do_page_fault modifies its own return address to point to the fault
> +#. exc_page_fault modifies its own return address to point to the fault
>     handle code and returns.

Ditto.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] Documentation: x86: Fix obsolete name of page fault handler

[Chih-En Lin]

Hi,
Thanks for reviewing.
I will fix all stuff mentioned.
Also, before submitting the next patch,
I will read/follow submitting-patch.rst carefully.

Thanks!