[yocto] [prelink-cross][PATCH] Support copy relocations in .data.rel.ro
Kyle Russell
bkylerussell at gmail.com
Fri Oct 12 07:06:22 PDT 2018
Do you want me to just resent my last two patches? I don't mind if that
would be easier, and I'll remember to add the Signed-off-by. :)
On Fri, Oct 12, 2018 at 10:00 AM Mark Hatle <mark.hatle at windriver.com>
wrote:
> On 10/4/18 9:12 AM, Kyle Russell wrote:
> > Hey Mark,
> >
> > Do you think this approach is reasonable? If so, I have another patch
> I'd like
> > to propose that would enable us to better catch error scenarios (like
> the last
> > two patches address) that we might encounter during do_image_prelink.
> We just
> > happened to detect these last two issues even though image_prelink
> didn't fail
> > the build, so I'd like to provide an option to enable a little more
> assertive
> > error path, if desired.
>
> I'm getting caught back up on my prelink 'TODO' set. The approach seems
> reasonable to me. However, I appear to have lost the reference to the
> original
> patch email.
>
> I'm going to try to reapply from this email (or the list archive), but I
> may
> need you to resend it. I'll let you [and others know] once I get these
> things
> merged.
>
> Thanks!
> --Mark
>
> > Thanks,
> > Kyle
> >
> > On Fri, Sep 28, 2018 at 10:57 AM Kyle Russell <bkylerussell at gmail.com
> > <mailto:bkylerussell at gmail.com>> wrote:
> >
> > binutils-2.28 (17026142ef35b62ac88bfe517b4160614902cb28) adds support
> > for copying read-only dynamic symbols into .data.rel.ro <
> http://data.rel.ro>
> > instead of .bss
> > since .bss is technically writable. This causes prelink to error
> out on
> > any binary containing COPY relocations in .data.rel.ro <
> http://data.rel.ro>.
> >
> > Read-only variables defined in shared libraries should be copied
> directly
> > into the space allocated for them in .data.rel.ro <
> http://data.rel.ro> by
> > the linker.
> >
> > To achieve this, we determine whether either of the two sections
> > containing copy relocations is .data.rel.ro <http://data.rel.ro>.
> If so, we
> > relocate the
> > symbol memory directly into the existing section instead of
> constructing
> > a new .(s)dynbss section once prelink_build_conflicts() returns.
> >
> > Fixes cxx1.sh, cxx2.sh, and cxx3.sh on Fedora 28 (which uses
> > binutils-2.29).
> > ---
> > src/conflict.c | 51
> +++++++++++++++++++++++++++++++++++++-------------
> > src/undo.c | 9 +++++++++
> > 2 files changed, 47 insertions(+), 13 deletions(-)
> >
> > diff --git a/src/conflict.c b/src/conflict.c
> > index 9ae2ddb..5613ace 100644
> > --- a/src/conflict.c
> > +++ b/src/conflict.c
> > @@ -450,7 +450,7 @@ get_relocated_mem (struct prelink_info *info,
> DSO *dso,
> > GElf_Addr addr,
> > int
> > prelink_build_conflicts (struct prelink_info *info)
> > {
> > - int i, ndeps = info->ent->ndepends + 1;
> > + int i, reset_dynbss = 0, reset_sdynbss = 0, ndeps =
> info->ent->ndepends + 1;
> > struct prelink_entry *ent;
> > int ret = 0;
> > DSO *dso;
> > @@ -675,6 +675,11 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > dso->filename);
> > goto error_out;
> > }
> > +
> > + name = strptr (dso, dso->ehdr.e_shstrndx,
> dso->shdr[bss1].sh_name);
> > + if (strcmp(name, ".data.rel.ro <http://data.rel.ro>") ==
> 0)
> > + reset_sdynbss = 1;
> > +
> > firstbss2 = i;
> > info->sdynbss_size = cr.rela[i - 1].r_offset -
> cr.rela[0].r_offset;
> > info->sdynbss_size += cr.rela[i - 1].r_addend;
> > @@ -702,6 +707,10 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > }
> > }
> >
> > + name = strptr (dso, dso->ehdr.e_shstrndx,
> dso->shdr[bss2].sh_name);
> > + if (strcmp(name, ".data.rel.ro <http://data.rel.ro>") == 0)
> > + reset_dynbss = 1;
> > +
> > info->dynbss_size = cr.rela[cr.count - 1].r_offset
> > - cr.rela[firstbss2].r_offset;
> > info->dynbss_size += cr.rela[cr.count - 1].r_addend;
> > @@ -719,9 +728,9 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > && strcmp (name = strptr (dso, dso->ehdr.e_shstrndx,
> > dso->shdr[bss1].sh_name),
> > ".dynbss") != 0
> > - && strcmp (name, ".sdynbss") != 0)
> > + && strcmp (name, ".sdynbss") != 0 && strcmp (name, ".
> data.rel.ro
> > <http://data.rel.ro>") != 0)
> > {
> > - error (0, 0, "%s: COPY relocations don't point into .bss
> or .sbss
> > section",
> > + error (0, 0, "%s: COPY relocations don't point into .bss,
> .sbss,
> > or .data.rel.ro <http://data.rel.ro> sections",
> > dso->filename);
> > goto error_out;
> > }
> > @@ -730,9 +739,9 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > && strcmp (name = strptr (dso, dso->ehdr.e_shstrndx,
> > dso->shdr[bss2].sh_name),
> > ".dynbss") != 0
> > - && strcmp (name, ".sdynbss") != 0)
> > + && strcmp (name, ".sdynbss") != 0 && strcmp (name, ".
> data.rel.ro
> > <http://data.rel.ro>") != 0)
> > {
> > - error (0, 0, "%s: COPY relocations don't point into .bss
> or .sbss
> > section",
> > + error (0, 0, "%s: COPY relocations don't point into .bss,
> .sbss,
> > or .data.rel.ro <http://data.rel.ro> section",
> > dso->filename);
> > goto error_out;
> > }
> > @@ -768,16 +777,21 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > }
> >
> > assert (j < ndeps);
> > + GElf_Addr symaddr = s->u.ent->base + s->value;
> > + char *buf;
> > +
> > if (i < firstbss2)
> > - j = get_relocated_mem (info, ndso, s->u.ent->base +
> s->value,
> > - info->sdynbss +
> cr.rela[i].r_offset
> > - - info->sdynbss_base,
> cr.rela[i].r_addend,
> > - cr.rela[i].r_offset);
> > + if (reset_sdynbss)
> > + buf = get_data(dso, cr.rela[i].r_offset, NULL, NULL);
> > + else
> > + buf = info->sdynbss + cr.rela[i].r_offset -
> info->sdynbss_base;
> > else
> > - j = get_relocated_mem (info, ndso, s->u.ent->base +
> s->value,
> > - info->dynbss + cr.rela[i].r_offset
> > - - info->dynbss_base,
> cr.rela[i].r_addend,
> > - cr.rela[i].r_offset);
> > + if (reset_dynbss)
> > + buf = get_data(dso, cr.rela[i].r_offset, NULL, NULL);
> > + else
> > + buf = info->dynbss + cr.rela[i].r_offset -
> info->dynbss_base;
> > +
> > + j = get_relocated_mem (info, ndso, symaddr, buf,
> > cr.rela[i].r_addend, cr.rela[i].r_offset);
> >
> > switch (j)
> > {
> > @@ -815,6 +829,17 @@ prelink_build_conflicts (struct prelink_info
> *info)
> > if (info->dsos[i])
> > close_dso (info->dsos[i]);
> >
> > + if (reset_sdynbss)
> > + {
> > + free (info->sdynbss);
> > + info->sdynbss = NULL;
> > + }
> > +
> > + if (reset_dynbss)
> > + {
> > + free (info->dynbss);
> > + info->dynbss = NULL;
> > + }
> > info->dsos = NULL;
> > free (cr.rela);
> > return ret;
> > diff --git a/src/undo.c b/src/undo.c
> > index 8a55bf2..4c38dab 100644
> > --- a/src/undo.c
> > +++ b/src/undo.c
> > @@ -633,6 +633,15 @@ prelink_undo (DSO *dso)
> > d->d_buf = NULL;
> > dso->shdr[i].sh_type = SHT_NOBITS;
> > }
> > + else if (dso->shdr[i].sh_type == SHT_PROGBITS
> > + && strcmp (name, ".data.rel.ro <
> http://data.rel.ro>") == 0)
> > + {
> > + scn = dso->scn[i];
> > + d = elf_getdata (scn, NULL);
> > + assert (d != NULL && elf_getdata (scn, d) == NULL);
> > + assert (d->d_size == dso->shdr[i].sh_size);
> > + assert (memset(d->d_buf, 0, d->d_size) == d->d_buf);
> > + }
> > else if (dso->shdr[i].sh_type == SHT_RELA
> > && shdr[i].sh_type == SHT_REL)
> > {
> > --
> > 2.17.1
> >
>
>
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