Subject: Re: [PATCH v1 04/10] asm-generic: Use HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR to define associated stubs

From: Helge Deller <[email-masked]>
Date: Tue, 12 Oct 2021 08:48:56 +0200

* Christophe Leroy <[email-masked]>:
>
>
> Le 12/10/2021 à 08:02, Helge Deller a écrit :
> > On 10/11/21 17:25, Christophe Leroy wrote:
> > > Use HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR instead of 'dereference_function_descriptor'
> > > to know whether arch has function descriptors.
> > >
> > > Signed-off-by: Christophe Leroy <[email-masked]>
> > > ---
> > >   arch/ia64/include/asm/sections.h    | 4 ++--
> > >   arch/parisc/include/asm/sections.h  | 6 ++++--
> > >   arch/powerpc/include/asm/sections.h | 6 ++++--
> > >   include/asm-generic/sections.h      | 3 ++-
> > >   4 files changed, 12 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
> > > index 35f24e52149a..80f5868afb06 100644
> > > --- a/arch/ia64/include/asm/sections.h
> > > +++ b/arch/ia64/include/asm/sections.h
> > > @@ -7,6 +7,8 @@
> > >    *	David Mosberger-Tang <[email-masked]>
> > >    */
> > >
> > > +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > +
> > >   #include <linux/elf.h>
> > >   #include <linux/uaccess.h>
> > >   #include <asm-generic/sections.h>
> > > @@ -27,8 +29,6 @@ extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_b
> > >   extern char __start_unwind[], __end_unwind[];
> > >   extern char __start_ivt_text[], __end_ivt_text[];
> > >
> > > -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > -
> > >   #undef dereference_function_descriptor
> > >   static inline void *dereference_function_descriptor(void *ptr)
> > >   {
> > > diff --git a/arch/parisc/include/asm/sections.h b/arch/parisc/include/asm/sections.h
> > > index bb52aea0cb21..2e781ee19b66 100644
> > > --- a/arch/parisc/include/asm/sections.h
> > > +++ b/arch/parisc/include/asm/sections.h
> > > @@ -2,6 +2,10 @@
> > >   #ifndef _PARISC_SECTIONS_H
> > >   #define _PARISC_SECTIONS_H
> > >
> > > +#ifdef CONFIG_64BIT
> > > +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > +#endif
> > > +
> > >   /* nothing to see, move along */
> > >   #include <asm-generic/sections.h>
> > >
> > > @@ -9,8 +13,6 @@ extern char __alt_instructions[], __alt_instructions_end[];
> > >
> > >   #ifdef CONFIG_64BIT
> > >
> > > -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > -
> > >   #undef dereference_function_descriptor
> > >   void *dereference_function_descriptor(void *);
> > >
> > > diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
> > > index 32e7035863ac..b7f1ba04e756 100644
> > > --- a/arch/powerpc/include/asm/sections.h
> > > +++ b/arch/powerpc/include/asm/sections.h
> > > @@ -8,6 +8,10 @@
> > >
> > >   #define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
> > >
> > > +#ifdef PPC64_ELF_ABI_v1
> > > +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > +#endif
> > > +
> > >   #include <asm-generic/sections.h>
> > >
> > >   extern bool init_mem_is_free;
> > > @@ -69,8 +73,6 @@ static inline int overlaps_kernel_text(unsigned long start, unsigned long end)
> > >
> > >   #ifdef PPC64_ELF_ABI_v1
> > >
> > > -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> > > -
> > >   #undef dereference_function_descriptor
> > >   static inline void *dereference_function_descriptor(void *ptr)
> > >   {
> > > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> > > index d16302d3eb59..1db5cfd69817 100644
> > > --- a/include/asm-generic/sections.h
> > > +++ b/include/asm-generic/sections.h
> > > @@ -59,7 +59,8 @@ extern char __noinstr_text_start[], __noinstr_text_end[];
> > >   extern __visible const void __nosave_begin, __nosave_end;
> > >
> > >   /* Function descriptor handling (if any).  Override in asm/sections.h */
> > > -#ifndef dereference_function_descriptor
> > > +#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
> > > +#else
> >
> > why not
> > #ifndef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
> > instead of #if/#else ?
>
> To avoid changing it again in patch 6, or getting an ugly #ifndef/#else at
> the end.

Ok.

Building on parisc fails at multiple files like this:
  CC      mm/filemap.o
In file included from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/interrupt.h:21,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/trace_recursion.h:5,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/ftrace.h:10,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/perf_event.h:49,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/trace_events.h:10,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/trace/syscall.h:7,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/include/linux/syscalls.h:87,
                 from /home/cvs/parisc/git-kernel/linus-linux-2.6/init/initramfs.c:11:
/home/cvs/parisc/git-kernel/linus-linux-2.6/arch/parisc/include/asm/sections.h:7:9: error: unknown type name ‘Elf64_Fdesc’
    7 | typedef Elf64_Fdesc funct_descr_t;
      |         ^~~~~~~~~~~

So, you still need e.g. this patch:

diff --git a/arch/parisc/include/asm/sections.h b/arch/parisc/include/asm/sections.h
index b041fb32a300..177983490e7c 100644
--- a/arch/parisc/include/asm/sections.h
+++ b/arch/parisc/include/asm/sections.h
@@ -4,6 +4,8 @@

 #ifdef CONFIG_64BIT
 #define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
+#include <asm/elf.h>
+#include <linux/uaccess.h>
 typedef Elf64_Fdesc funct_descr_t;
 #endif

In general to save space I think it would be beneficial if the
dereference_kernel_function_descriptor() and
dereference_kernel_function_descriptor() functions would go as real
functions a c-file instead of just being inlined functions in the
asm-generic/sections.h header file.

Other than that it's a nice cleanup!

Helge