Ping^2 ? As a reminder, this patch mimics what aarch64 does wrt to references to weak symbols such that they are not resolved by the assembler, in case a strong definition overrides the local one at link time.
Christophe On 8 December 2016 at 09:17, Christophe Lyon <christophe.l...@linaro.org> wrote: > Ping? > > On 1 December 2016 at 15:27, Christophe Lyon <christophe.l...@linaro.org> > wrote: >> Hi, >> >> >> On 10 November 2016 at 15:10, Christophe Lyon >> <christophe.l...@linaro.org> wrote: >>> On 10 November 2016 at 11:05, Richard Earnshaw >>> <richard.earns...@foss.arm.com> wrote: >>>> On 09/11/16 21:29, Christophe Lyon wrote: >>>>> Hi, >>>>> >>>>> PR 78253 shows that the handling of weak references has changed for >>>>> ARM with gcc-5. >>>>> >>>>> When r220674 was committed, default_binds_local_p_2 gained a new >>>>> parameter (weak_dominate), which, when true, implies that a reference >>>>> to a weak symbol defined locally will be resolved locally, even though >>>>> it could be overridden by a strong definition in another object file. >>>>> >>>>> With r220674, default_binds_local_p forces weak_dominate=true, >>>>> effectively changing the previous behavior. >>>>> >>>>> The attached patch introduces default_binds_local_p_4 which is a copy >>>>> of default_binds_local_p_2, but using weak_dominate=false, and updates >>>>> the ARM target to call default_binds_local_p_4 instead of >>>>> default_binds_local_p_2. >>>>> >>>>> I ran cross-tests on various arm* configurations with no regression, >>>>> and checked that the test attached to the original bugzilla now works >>>>> as expected. >>>>> >>>>> I am not sure why weak_dominate defaults to true, and I couldn't >>>>> really understand why by reading the threads related to r220674 and >>>>> following updates to default_binds_local_p_* which all deal with other >>>>> corner cases and do not discuss the weak_dominate parameter. >>>>> >>>>> Or should this patch be made more generic? >>>>> >>>> >>>> I certainly don't think it should be ARM specific. >>> That was my feeling too. >>> >>>> >>>> The questions I have are: >>>> >>>> 1) What do other targets do today. Are they the same, or different? >>> >>> arm, aarch64, s390 use default_binds_local_p_2 since PR 65780, and >>> default_binds_local_p before that. Both have weak_dominate=true >>> i386 has its own version, calling default_binds_local_p_3 with true >>> for weak_dominate >>> >>> But the behaviour of default_binds_local_p changed with r220674 as I said >>> above. >>> See https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=220674 and >>> notice how weak_dominate was introduced >>> >>> The original bug report is about a different case: >>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32219 >>> >>> The original patch submission is >>> https://gcc.gnu.org/ml/gcc-patches/2015-02/msg00410.html >>> and the 1st version with weak_dominate is in: >>> https://gcc.gnu.org/ml/gcc-patches/2015-02/msg00469.html >>> but it's not clear to me why this was introduced >>> >>>> 2) If different why? >>> on aarch64, although binds_local_p returns true, the relocations used when >>> building the function pointer is still the same (still via the GOT). >>> >>> aarch64 has different logic than arm when accessing a symbol >>> (eg aarch64_classify_symbol) >>> >>>> 3) Is the current behaviour really what was intended by the patch? ie. >>>> Was the old behaviour actually wrong? >>>> >>> That's what I was wondering. >>> Before r220674, calling a weak function directly or via a function >>> pointer had the same effect (in other words, the function pointer >>> points to the actual implementation: the strong one if any, the weak >>> one otherwise). >>> >>> After r220674, on arm the function pointer points to the weak >>> definition, which seems wrong to me, it should leave the actual >>> resolution to the linker. >>> >>> >> >> After looking at the aarch64 port, I think that references to weak symbols >> have to be handled carefully, to make sure they cannot be resolved >> by the assembler, since the weak symbol can be overridden by a strong >> definition at link-time. >> >> Here is a new patch which does that. >> Validated on arm* targets with no regression, and I checked that the >> original testcase now executes as expected. >> >> Christophe >> >> >>>> R. >>>>> Thanks, >>>>> >>>>> Christophe >>>>> >>>>
