On Fri, Sep 24, 2021 at 11:29 AM H.J. Lu <hjl.to...@gmail.com> wrote: > > On Fri, Sep 24, 2021 at 11:14 AM Fāng-ruì Sòng <mask...@google.com> wrote: > > > > On Fri, Sep 24, 2021 at 10:41 AM H.J. Lu <hjl.to...@gmail.com> wrote: > > > > > > On Fri, Sep 24, 2021 at 10:29 AM Fāng-ruì Sòng <mask...@google.com> wrote: > > > > > > > > On Tue, Sep 21, 2021 at 7:08 PM Fāng-ruì Sòng <mask...@google.com> > > > > wrote: > > > > > > > > > > On Tue, Sep 21, 2021 at 6:57 PM H.J. Lu <hjl.to...@gmail.com> wrote: > > > > > > > > > > > > On Tue, Sep 21, 2021 at 9:16 AM Uros Bizjak <ubiz...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > > On Mon, Sep 20, 2021 at 8:20 PM Fāng-ruì Sòng via Gcc-patches > > > > > > > <gcc-patches@gcc.gnu.org> wrote: > > > > > > > > > > > > > > > > PING^5 > > > > > > > > https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html > > > > > > > > > > > > > > > > On Sat, Sep 4, 2021 at 12:11 PM Fāng-ruì Sòng > > > > > > > > <mask...@google.com> wrote: > > > > > > > > > > > > > > > > > > PING^4 > > > > > > > > > https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html > > > > > > > > > > > > > > > > > > One major design goal of PIE was to avoid copy relocations. > > > > > > > > > The original patch for GCC 5 caused problems for many years. > > > > > > > > > > > > > > > > > > On Wed, Aug 18, 2021 at 11:54 PM Fāng-ruì Sòng > > > > > > > > > <mask...@google.com> wrote: > > > > > > > > >> > > > > > > > > >> PING^3 > > > > > > > > >> https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html > > > > > > > > >> > > > > > > > > >> On Fri, Jun 4, 2021 at 3:04 PM Fāng-ruì Sòng > > > > > > > > >> <mask...@google.com> wrote: > > > > > > > > >> > > > > > > > > > >> > PING^2 > > > > > > > > >> > https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html > > > > > > > > >> > > > > > > > > > >> > On Mon, May 24, 2021 at 9:43 AM Fāng-ruì Sòng > > > > > > > > >> > <mask...@google.com> wrote: > > > > > > > > >> > > > > > > > > > > >> > > Ping > > > > > > > > >> > > https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html > > > > > > > > >> > > > > > > > > > > >> > > On Tue, May 11, 2021 at 8:29 PM Fangrui Song > > > > > > > > >> > > <mask...@google.com> wrote: > > > > > > > > >> > > > > > > > > > > > >> > > > This was introduced in 2014-12 to use local binding > > > > > > > > >> > > > for external symbols > > > > > > > > >> > > > for -fPIE. Now that we have H.J. Lu's GOTPCRELX for > > > > > > > > >> > > > years which mostly > > > > > > > > >> > > > nullify the benefit of HAVE_LD_PIE_COPYRELOC, > > > > > > > > >> > > > HAVE_LD_PIE_COPYRELOC > > > > > > > > >> > > > should retire now. > > > > > > > > >> > > > > > > > > > > > >> > > > One design goal of -fPIE was to avoid copy relocations. > > > > > > > > >> > > > HAVE_LD_PIE_COPYRELOC has deviated from the goal. > > > > > > > > >> > > > With this change, the > > > > > > > > >> > > > -fPIE behavior of x86-64 will be closer to x86-32 and > > > > > > > > >> > > > other targets. > > > > > > > > >> > > > > > > > > > > > >> > > > --- > > > > > > > > >> > > > > > > > > > > > >> > > > See > > > > > > > > >> > > > https://gcc.gnu.org/legacy-ml/gcc/2019-05/msg00215.html > > > > > > > > >> > > > for a list > > > > > > > > >> > > > of fixed and unfixed (e.g. gold incompatibility with > > > > > > > > >> > > > protected > > > > > > > > >> > > > https://sourceware.org/bugzilla/show_bug.cgi?id=19823) > > > > > > > > >> > > > issues. > > > > > > > > >> > > > > > > > > > > > >> > > > If you prefer a longer write-up, see > > > > > > > > >> > > > https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected > > > > > > > > >> > > > --- > > > > > > > > >> > > > gcc/config.in | 6 --- > > > > > > > > >> > > > gcc/config/i386/i386.c | 11 > > > > > > > > >> > > > +--- > > > > > > > > >> > > > gcc/configure | 52 > > > > > > > > >> > > > ------------------- > > > > > > > > >> > > > gcc/configure.ac | 48 > > > > > > > > >> > > > ----------------- > > > > > > > > >> > > > gcc/doc/sourcebuild.texi | 3 -- > > > > > > > > >> > > > .../gcc.target/i386/pie-copyrelocs-1.c | 14 > > > > > > > > >> > > > ----- > > > > > > > > >> > > > .../gcc.target/i386/pie-copyrelocs-2.c | 14 > > > > > > > > >> > > > ----- > > > > > > > > >> > > > .../gcc.target/i386/pie-copyrelocs-3.c | 14 > > > > > > > > >> > > > ----- > > > > > > > > >> > > > .../gcc.target/i386/pie-copyrelocs-4.c | 17 > > > > > > > > >> > > > ------ > > > > > > > > >> > > > gcc/testsuite/lib/target-supports.exp | 47 > > > > > > > > >> > > > ----------------- > > > > > > > > >> > > > 10 files changed, 2 insertions(+), 224 deletions(-) > > > > > > > > >> > > > delete mode 100644 > > > > > > > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c > > > > > > > > >> > > > delete mode 100644 > > > > > > > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c > > > > > > > > >> > > > delete mode 100644 > > > > > > > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c > > > > > > > > >> > > > delete mode 100644 > > > > > > > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c > > > > > > > > > > > > > > From x86 maintainer's PoV, the implementation is trivially > > > > > > > correct, > > > > > > > but I have no idea about functionality. HJ, can you please review > > > > > > > the > > > > > > > functionality and post your opinion on the patch to move it > > > > > > > forward? > > > > > > > > > > > > > > Thanks, > > > > > > > Uros. > > > > > > > > > > > > I prefer to leave it alone and apply this: > > > > > > > > > > > > https://gcc.gnu.org/pipermail/gcc-patches/2021-August/576736.html > > > > > > > > > > > > instead. I am working to add a nodirect_extern_access attribute > > > > > > based > > > > > > on feedback at LPC 2021. > > > > > > > > > > I think -fpie should be fixed as soon as possible. > > > > > > > > > > "Add -f[no-]direct-extern-access" says "-fdirect-extern-access is the > > > > > default." > > > > > IMHO this is not a good choice for -fpie. > > > > > As the description of this patch says, one of the design goals of > > > > > -fpie is to avoid copy relocations. > > > > > > > > > > > In executable and shared library, bind symbols with the > > > > > > STV_PROTECTED visibility locally > > > > > > > > > > As I have repeated many times (also Clang's behavior), STV_PROTECTED > > > > > visibility symbol should be bound locally regardless of > > > > > -fno-direct-extern-access. > > > > > > > > > > I think it is fair to say all of Michael Matz, Alan Modra, and I think > > > > > adding so many behaviors under -fno-direct-extern-access is > > > > > over-engineering (well, because I don't think > > > > > -fno-direct-extern-access can be selected as the default behavior any > > > > > time soon). > > > > > > > > > > https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected#summary > > > > > > > > -fno-direct-extern-access should focus on the semantics of non-pic > > > > code, which is the traditional configuration which may introduce copy > > > > relocations. > > > > An important design goal of -fpie/-fPIE was to avoid copy relocations. > > > > The 2014 x86-64 patch deviated the direction (I am sorry that some > > > > Google folks originated it) and the revert is long due. I am glad that > > > > all other architectures still keep the nice property that -fpie/-fPIE > > > > never introduces copy relocations. > > > > > > > > -fdirect-extern-access can do something with -fpie/-fPIE but I doubt > > > > anyone may enable it to get the small size benefit. > > > > The -f(no-)?direct-extern-access patch doesn't need to check > > > > HAVE_LD_PIE_COPYRELOC. > > > > The few users (if ever exist) who use -fpie -fdirect-extern-access > > > > should ensure their GNU ld supports copy relocations by themselves. > > > > GCC configure doesn't need to pay the availability check cost. The > > > > support has been available for many years (~2014/2015). > > > > > > I'd like to get rid of copy relocation for both PIE and non-PIE. But > > > we should keep copy relocation as an option for both PIE and non-PIE > > > if people ask for it. > > > > They still have a copy relocation option for PIE with your > > -fdirect-extern-access :) > > This is the whole point.
Then can a maintainer apply the patch? The (to-be-reverted) original x86-64 -fpie/-fPIE patch is a dangerous and micro optimization which has caused continuous pain, also an outlier from all sane architectures even including x86-32. By default users should get no copy relocation with -fpie/-fPIE. When H.J.'s -fdirect-extern-access lands, the users who want to play danger can still get the micro optimization. > > People's complaints are about the default behavior for PIE: on all > > other architectures, the default code generation should avoid copy > > relocations. > > For example the Qt issue (https://bugreports.qt.io/browse/QTBUG-45755) > > was related to GCC 5 x86-64 switching to copy relocations behavior for > > PIE. > > Qt folks forced PIC to avoid copy relocations. > > > > > > -f(no-)?direct-extern-access is a great addition. (As I previously > > mentioned I have some small reservation whether a GNU property should > > be used, but that is minor preference.) > > I don't mind -fno-pic defaulting to -fno-direct-extern-access like > > mips in the future. > > But I do mind whether PIE users need to explicitly specify > > -fno-direct-extern-access to avoid copy relocations. > > Like most other architecture and Clang x86-64, they should not need to > > specify anything. > > They shouldn't need a GNU property to prevent that. > > > > > > I hope I've given sufficient justification why I think this revert is > > still useful with your -f(no-)direct-extern-access.
