On Tue, Jun 27, 2017 at 11:20:02AM +1000, Kugan Vivekanandarajah wrote: > https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00614.html added this > workaround to get kernel building with when TARGET_FIX_ERR_A53_843419 > is enabled. > > This was added to support building kernel loadable modules. In kernel, > when CONFIG_ARM64_ERRATUM_843419 is selected, the relocation needed > for ADRP/LDR (R_AARCH64_ADR_PREL_PG_HI21 and > R_AARCH64_ADR_PREL_PG_HI21_NC are removed from the kernel to avoid > loading objects with possibly offending sequence). Thus, it could only > support pc relative literal loads. > > However, the following patch was posted to kernel to add > -mpc-relative-literal-loads > http://www.spinics.net/lists/arm-kernel/msg476149.html > > -mpc-relative-literal-loads is unconditionally added to the kernel > build as can be seen from: > https://github.com/torvalds/linux/blob/master/arch/arm64/Makefile > > Therefore this patch removes the hunk so that applications like > SPECcpu2017's 521/621.wrf can be built (with LTO in this case) without > -mno-pc-relative-literal-loads > > Bootstrapped and regression tested on aarch64-linux-gnu with no new > regressions. > > Is this OK for trunk?
Hi Kugan, I'm struggling a little to convince myself that this is correct. I think the argument is that this was a workaround for one very particular issue with the linux kernel module loader, which hard faults by refusing to handle these relocations when in a workaround mode for Erratum 843419. Most of these relocations won't occur because the kernel builds with -mcmodel=large, but literals would always use a small model style adrp/load, unless we were using -mpc-relative-literal-loads . So, this workaround enabled -mpc-relative-literal-loads always when we were in a workaround mode, thus allowing the kernel loader to continue. The argument for removing it then, is that with the kernel now always using -mpc-relative-literal-loads there is no reason for this workaround to stay in place. The linkers which we will use will apply the workaround if needed. Testcases and a detailed problem report of the build failures you had seen in 521.wrf would have helped me get closer to understanding this, and made review substantially easier. Am I on the right track? If so, this is OK for trunk. If not, please can you expand on what is going on in this patch. Thanks, James > > Thanks, > Kugan > > gcc/testsuite/ChangeLog: > > 2017-06-27 Kugan Vivekanandarajah <kug...@linaro.org> > > * gcc.target/aarch64/pr63304_1.c: Remove-mno-fix-cortex-a53-843419. > > gcc/ChangeLog: > > 2017-06-27 Kugan Vivekanandarajah <kug...@linaro.org> > > * config/aarch64/aarch64.c (aarch64_override_options_after_change_1): > Disable pc relative literal load irrespective of TARGET_FIX_ERR_A53_84341 > for default.
