[PATCH 0/2] ARC Moving to @pcl relocations
Andrew Burgess
andrew.burgess at embecosm.com
Fri Jul 29 06:26:09 PDT 2016
* Andrew Burgess <andrew.burgess at embecosm.com> [2016-07-29 10:43:17 +0100]:
> * Alexey Brodkin <Alexey.Brodkin at synopsys.com> [2016-07-29 08:49:22 +0000]:
>
> > Hi Andrew, all,
> >
> > On Thu, 2016-07-28 at 15:40 -0700, Vineet Gupta wrote:
> > > On 07/28/2016 03:04 PM, Bernhard Reutner-Fischer wrote:
> > > >
> > > > >
> > > > > Indeed your 2/2 seems to be the most "past-proof" code change. So I
> > > > > >
> > > > > > would think it
> > > > > > is indeed better and is something I should have done in the first
> > > > > > place.
> > > > > >
> > > > > > @Alexey, @Vlad what say you ?
> > > > uClibc traditionally supports the current stable release of binutils, which would make it patch #1 I think.
> > > >
> > >
> > > But 2/2 works for both and makes actual binutils version moot. FWIW, ARC tools
> > > don't as of last release didn't use the upstream/stable binutils, but we are
> > > pretty close to that now though.
> >
> > Personally I'd prefer to not add more conditional defines in uClibc but
> > make it a little-bit simpler.
> >
> > I.e. either Vlad's patch or #1 from this series IMHO looks better.
> > It's been quite some time since we updated our tools with PCL support
> > and I'm not really sure if there's anybody interested in using ages old
> > tools with today's uClibc. We don't test such combinations and there could
> > be issues already in such combos.
> >
> > BTW I noticed that Vlad's patch removes/reverts that thing as well:
> > http://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/commit/ldso/ldso/arc/dl-sysdep.h?id=181d410ad00cddd1d6c9f4835e129136b74
> > c5187
> >
> > While Andrew just replaces ".&" construction with "@pcl".
> > I'm wondering which is the correct approach here?
>
> I left the second block in as the two blocks use different symbols,
> the native threads block uses _DYNAMIC, while the non-native uses
> _dl_start.
>
> I wasn't sure if this was significant, so left the the split in
> place. If more knowledgeable folk believe these can be combined then
> that's fine with me (so long as we combine on @pcl).
Having looked at this a little more I think that we should merge the
section Alexey mentioned above. In the second instance (the one I
modified) we use the symbol _dl_start, while in the first we use
_DYNAMIC.
However, the comment in the first block makes it clear the symbol used
should be a global symbol, not a local, and _dl_start is a local
symbol.
The consequence of using a local here is that we end up with a
R_ARC_NONE relocation being generated again the .got.
[ The generation of the R_ARC_NONE is probably a bug, or at least a
lack of optimisation, but it is what happens with the current
upstream tools. ]
As the arc dynamic loader does not currently support patching
R_ARC_NONE during the bootstrap phase, if uClibc(-ng) is configured
without native threads, then currently we get a dynamic loader that
does not work.
So, I think we should collapse both sections, and make use of the
_DYNAMIC symbol instead of _dl_start. I've included a revised version
of patch 1/2 that includes this latest change.
Thanks,
Andrew
----
[PATCH] ARC: Update relocation syntax for old-thread model code
This commit reverses a change introduced in commit 20554a78a9bba that
split some of the ARC code into two based on whether uClibc was
configured with native threads or not.
The native thread code was updated to use the relocation syntax of
modern binutils, while the non-native code path used a syntax only
accepted in older versions of binutils.
The problem with this is that the choice of old binutils or not is
orthogonal to the choice of native threads or not, and so, inevitably a
user with a recent version of binutils can make the choice to configure
uClibc with non-native thread support, and run into code that will not
assemble.
The solution is either to abandon support for the old tools completely,
or to add a new compile time flag for ARC that is set when the version
of binutils being used is old; this new flag would allow the old
relocation structure to be selected.
In this commit I have simply dropped support for older versions of the
tools.
---
ldso/ldso/arc/dl-startup.h | 7 -------
ldso/ldso/arc/dl-sysdep.h | 10 ----------
2 files changed, 17 deletions(-)
diff --git a/ldso/ldso/arc/dl-startup.h b/ldso/ldso/arc/dl-startup.h
index ef89b53..664b860 100644
--- a/ldso/ldso/arc/dl-startup.h
+++ b/ldso/ldso/arc/dl-startup.h
@@ -34,15 +34,8 @@ __asm__(
" ; skip the extra args calc by dl_start() \n"
" ld_s r1, [sp] ; orig argc from aux-vec Tbl \n"
-#ifdef __UCLIBC_HAS_THREADS_NATIVE__
" ld r12, [pcl, _dl_skip_args at pcl] \n"
-
" add r2, pcl, _dl_fini at pcl ; finalizer \n"
-#else
- " add r12, pcl, _dl_skip_args-.+(.&2) \n"
- " ld r12, [r12] \n"
- " add r2, pcl, _dl_fini-.+(.&2) ; finalizer \n"
-#endif
" add2 sp, sp, r12 ; discard argv entries from stack\n"
" sub_s r1, r1, r12 ; adjusted argc, on stack \n"
diff --git a/ldso/ldso/arc/dl-sysdep.h b/ldso/ldso/arc/dl-sysdep.h
index caece99..c6086e6 100644
--- a/ldso/ldso/arc/dl-sysdep.h
+++ b/ldso/ldso/arc/dl-sysdep.h
@@ -132,7 +132,6 @@ static __always_inline Elf32_Addr elf_machine_dynamic(void)
/* Return the run-time load address of the shared object. */
static __always_inline Elf32_Addr elf_machine_load_address(void)
{
-#ifdef __UCLIBC_HAS_THREADS_NATIVE__
/* To find the loadaddr we subtract the runtime addr of a non-local symbol
* say _DYNAMIC from it's build-time addr.
* N.B., gotpc loads get optimized by the linker if it finds the symbol
@@ -150,15 +149,6 @@ static __always_inline Elf32_Addr elf_machine_load_address(void)
"sub %0, %0, %1 ;delta" "\n"
: "=&r" (addr), "=r"(tmp)
);
-#else
- Elf32_Addr addr, tmp;
- __asm__ (
- "ld %1, [pcl, _dl_start at gotpc] ;build addr of _dl_start \n"
- "add %0, pcl, _dl_start-.+(.&2) ;runtime addr of _dl_start \n"
- "sub %0, %0, %1 ;delta \n"
- : "=&r" (addr), "=r"(tmp)
- );
-#endif
return addr;
}
--
2.5.1
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