On Fri, Jun 18, 2021 at 2:34 PM Fangrui Song <mask...@google.com> wrote: > > On 2021-06-18, H.J. Lu via llvm-dev wrote: > >Add GNU_PROPERTY_1_NEEDED: > > > > #define GNU_PROPERTY_1_NEEDED GNU_PROPERTY_UINT32_OR_LO > > > >to indicate the needed properties by the object file. > > > > I am fine with this logical OR style usage. But see below, do we need it > for ld.so runtime check?
I implemented run-time check on users/hjl/single-global/master branch: https://gitlab.com/x86-glibc/glibc/-/commits/users/hjl/single-global/master with tests: [hjl@gnu-cfl-2 build-x86_64-linux]$ elf/tst-protected1a copy relocation against non-copyable protected symbol=protected1 in file=/export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/elf/tst-protected1moda.so [hjl@gnu-cfl-2 build-x86_64-linux]$ elf/tst-protected2a `protected1' in main and moda doesn't have the same address non-canonical reference to canonical protected function symbol=protected1 in file=/export/build/gnu/tools-build/glibc-cet-gitlab/build-x86_64-linux/elf/tst-protected2moda.so [hjl@gnu-cfl-2 build-x86_64-linux]$ I prefer these over random run-time failures. > (As I mentioned previously, I do not know how an AND-style property can > be used/deployed if old object files without the .note.gnu.property is > considered to have a value of 0.) > > >Add GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION: > > > > #define GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION (1U << 0) > > > >to indicate that the object file requires canonical function pointers and > >cannot be used with copy relocation. > > In https://sourceware.org/pipermail/gnu-gabi/2021q2/000481.html you gave > a rationale > > "The issue is that libfoo.so used in link-time can be different from > libfoo.so at run-time. The symbol, foobar, in libfoo.so at link-time > has the default visibility. But foobar in libfoo.so at run-time can be > protected. ld.so should detect such cases which can lead to run-time > failures." > > First, I think such dynamic symbol visibility change is uncommon. I can imagine that some libraries want to switch to protected symbols. > Second, if ld.so finds that a symbol lookup for (st_value==0 > st_shndx==SHN_UNDEF) will bind to a STV_PROTECTED definition in a shared > object, can the diagnostic be moved there? > The compatibility property is per-symbol and the symbol lookup is a > perfect place for a diagnostic, like a symbol versioning error. > > > I guess GCC folks may get noticed if you start a thread adding > -fsingle-global-definition, otherwise many people who have opinions may > just ignore threads about GNU PROPERTY addition. Binutils changes are at https://gitlab.com/x86-binutils/binutils-gdb/-/tree/users/hjl/property/master GCC changes are next. > > > >The PDF file is at > > > >https://gitlab.com/x86-psABIs/Linux-ABI/-/wikis/uploads/9eca2f2defe62b0c5015bf2e3e8a9f05/Linux-gABI-1_needed-2021-06-18.pdf -- H.J.
