Re: [PATCH v6 01/14] Rewrite abi-note.S in C.

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Jul 1, 2020 at 10:31 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>
> The 07/01/2020 07:41, H.J. Lu wrote:
> > On Wed, Jul 1, 2020 at 7:38 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > > Using C code allows the compiler to add target specific object file
> > > markings based on CFLAGS.
> > >
> > > The arm specific abi-note.S is removed and similar object file fix
> > > up will be avoided on AArch64 with standard branch-prtection.
> > > ---
> > >  csu/{abi-note.S => abi-note.c} | 23 +++++++++++++----------
> > >  sysdeps/arm/abi-note.S         |  8 --------
> > >  2 files changed, 13 insertions(+), 18 deletions(-)
> > >  rename csu/{abi-note.S => abi-note.c} (90%)
> > >  delete mode 100644 sysdeps/arm/abi-note.S
> > >
> > > diff --git a/csu/abi-note.S b/csu/abi-note.c
> > > similarity index 90%
> > > rename from csu/abi-note.S
> > > rename to csu/abi-note.c
> > > index 2b4b5f8824..db195c7ab7 100644
> > > --- a/csu/abi-note.S
> > > +++ b/csu/abi-note.c
> > > @@ -53,6 +53,8 @@ offset        length  contents
> > >     identify the earliest release of that OS that supports this ABI.
> > >     See abi-tags (top level) for details. */
> > >
> > > +#include <link.h>
> > > +#include <stdint.h>
> > >  #include <config.h>
> > >  #include <abi-tag.h>           /* OS-specific ABI tag value */
> > >
> > > @@ -60,13 +62,14 @@ offset      length  contents
> > >     name begins with `.note' and creates a PT_NOTE program header entry
> > >     pointing at it. */
> > >
> > > -       .section ".note.ABI-tag", "a"
> > > -       .p2align 2
> > > -       .long 1f - 0f           /* name length */
> > > -       .long 3f - 2f           /* data length */
> > > -       .long  1                /* note type */
> > > -0:     .asciz "GNU"            /* vendor name */
> > > -1:     .p2align 2
> > > -2:     .long __ABI_TAG_OS      /* note data: the ABI tag */
> > > -       .long __ABI_TAG_VERSION
> > > -3:     .p2align 2              /* pad out section */
> > > +__attribute__ ((used, aligned (4), section (".note.ABI-tag")))
> > > +static const struct
> > > +{
> > > +  ElfW(Nhdr) nhdr;
> > > +  char name[4];
> > > +  int32_t desc[4];
> > > +} __abi_tag = {
> > > +  { .n_namesz = 4, .n_descsz = 16, .n_type = 1 },
> >
> > sizeof "GNU"? and sizeof desc?
>
> i can do
>
>   { .n_namesz = sizeof __abi_tag.name,
>     .n_descsz = sizeof __abi_tag.desc,
>     .n_type = 1 },
>
> is that better? (for me the int literal looks
> clear in the context and shorter. i don't like
> sizeof "GNU" i think that's less clear.)

It is better.

-- 
H.J.