Ping? The patch is at https://gcc.gnu.org/ml/gcc-patches/2016-12/msg00078.html
On 14 December 2016 at 16:29, Christophe Lyon <christophe.l...@linaro.org> wrote: > 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 >>>>>> >>>>>