From: Wei Liu <wei.liu2@citrix.com>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Wei Liu <wei.liu2@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH] libxc: elf_kernel loader: Remove check for shstrtab
Date: Thu, 16 May 2019 14:23:52 +0100 [thread overview]
Message-ID: <20190516132352.GF2798@zion.uk.xensource.com> (raw)
Message-ID: <20190516132352.vGinPKaVsD8IDvAcPvWC9uUtQ3_u9FH3q-8tiipLJPQ@z> (raw)
In-Reply-To: <20190515125530.GB1245@perard.uk.xensource.com>
On Wed, May 15, 2019 at 01:55:30PM +0100, Anthony PERARD wrote:
> On Wed, May 15, 2019 at 01:07:03PM +0100, Andrew Cooper wrote:
> > On 15/05/2019 12:40, Anthony PERARD wrote:
> > > This was probably useful to load ELF Note, but now ELF notes
> > > "should live in a PT_NOTE segment" (elfnote.h).
> > >
> > > With notes living in segment, there are no need for sections, so there
> > > is nothing to be stored in the shstrtab.
> > >
> > > This patch would allow to write a simpler ELF header for an OVMF blob
> > > (which isn't an ELF) and allow it to be loaded as a PVH kernel. The
> > > header only needs to declare two program segments:
> > > - one to tell an ELF loader where to put the blob,
> > > - one for a Xen ELFNOTE.
> > >
> > > The ELFNOTE is to comply to the pvh design which wants the
> > > XEN_ELFNOTE_PHYS32_ENTRY to declare a blob as compaptible with the PVH
> > > boot ABI.
> > >
> > > Note that without the ELFNOTE, libxc will load an ELF but with
> > > the plain ELF loader, which doesn't check for shstrtab.
> > >
> > > Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> > > ---
> > > tools/libxc/xc_dom_elfloader.c | 9 ---------
> > > 1 file changed, 9 deletions(-)
> > >
> > > diff --git a/tools/libxc/xc_dom_elfloader.c b/tools/libxc/xc_dom_elfloader.c
> > > index 82b5f2ee79..b327db219d 100644
> > > --- a/tools/libxc/xc_dom_elfloader.c
> > > +++ b/tools/libxc/xc_dom_elfloader.c
> > > @@ -165,15 +165,6 @@ static elf_negerrnoval xc_dom_parse_elf_kernel(struct xc_dom_image *dom)
> > > return rc;
> > > }
> > >
> > > - /* Find the section-header strings table. */
> > > - if ( ELF_PTRVAL_INVALID(elf->sec_strtab) )
> > > - {
> > > - xc_dom_panic(dom->xch, XC_INVALID_KERNEL, "%s: ELF image"
> > > - " has no shstrtab", __FUNCTION__);
> > > - rc = -EINVAL;
> > > - goto out;
> > > - }
> >
> > This might be fine for newer binaries, but you'll break older ones.
> >
> > Instead, you should skip searching for strtab if we've already located
> > the Xen notes.
>
> :-(, maybe I should have gone futher on explaining why this check is
> useless (and probably at the wrong place, at least now).
>
> The next thing that's done after that check is:
> elf_parse_binary()
> elf_xen_parse()
> Those are located in "xen/common/libelf", and those are the functions
> that actually takes care of extracting data from the elf.
>
> elf_xen_parse() first look for Xen ELFNOTE in the program segments
> (phdr, PT_NOTE) and skip reading section and strtab if found.
>
> So, libelf already does what you asked for ;-).
>
> The shstrtab are only used to look for legacy __xen_guest section names.
> Since ELFNOTEs was used, the name of section aren't looked at.
>
> I hope that help.
>
Andrew, do you still have concern?
Wei.
> Thanks,
>
> --
> Anthony PERARD
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next prev parent reply other threads:[~2019-05-16 13:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-15 11:40 [PATCH] libxc: elf_kernel loader: Remove check for shstrtab Anthony PERARD
2019-05-15 11:40 ` [Xen-devel] " Anthony PERARD
2019-05-15 12:02 ` Wei Liu
2019-05-15 12:02 ` [Xen-devel] " Wei Liu
2019-05-15 12:07 ` Andrew Cooper
2019-05-15 12:07 ` [Xen-devel] " Andrew Cooper
2019-05-15 12:09 ` Wei Liu
2019-05-15 12:09 ` [Xen-devel] " Wei Liu
2019-05-15 12:55 ` Anthony PERARD
2019-05-15 12:55 ` [Xen-devel] " Anthony PERARD
2019-05-16 13:23 ` Wei Liu [this message]
2019-05-16 13:23 ` Wei Liu
2019-05-16 13:38 ` Andrew Cooper
2019-05-16 13:38 ` [Xen-devel] " Andrew Cooper
2019-05-17 11:38 ` [PATCH v2] " Anthony PERARD
2019-05-17 11:38 ` [Xen-devel] " Anthony PERARD
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