On Thu, Jun 17, 2021 at 12:38 PM Fangrui Song <mask...@google.com> wrote: > > On 2021-06-17, H.J. Lu via llvm-dev wrote: > >On Thu, Jan 21, 2021 at 7:02 AM H.J. Lu <hjl.to...@gmail.com> wrote: > >> > >> On Wed, Jan 13, 2021 at 9:06 AM H.J. Lu <hjl.to...@gmail.com> wrote: > >> > > >> > 1. GNU_PROPERTY_UINT32_AND_LO..GNU_PROPERTY_UINT32_AND_HI > >> > > >> > #define GNU_PROPERTY_UINT32_AND_LO 0xb0000000 > >> > #define GNU_PROPERTY_UINT32_AND_HI 0xb0007fff > >> > > >> > A bit in the output pr_data field is set only if it is set in all > >> > relocatable input pr_data fields. If all bits in the the output > >> > pr_data field are zero, this property should be removed from output. > >> > > >> > If the bit is 1, all input relocatables have the feature. If the > >> > bit is 0 or the property is missing, the info is unknown. > > How to use AND in practice? > Are you going to add .note.gnu.property to all of crt1.o crti.o > crtbegin.o crtend.o crtn.o and miscellaneous libc_nonshared.a object > files written in assembly? > > >> > 2. GNU_PROPERTY_UINT32_OR_LO..GNU_PROPERTY_UINT32_OR_HI > >> > > >> > #define GNU_PROPERTY_UINT32_OR_LO 0xb0008000 > >> > #define GNU_PROPERTY_UINT32_OR_HI 0xb000ffff > >> > > >> > A bit in the output pr_data field is set if it is set in any > >> > relocatable input pr_data fields. If all bits in the the output > >> > pr_data field are zero, this property should be removed from output. > >> > > >> > If the bit is 1, some input relocatables have the feature. If the > >> > bit is 0 or the property is missing, the info is unknown. > >> > > >> > The PDF is at > >> > > >> > https://gitlab.com/x86-psABIs/Linux-ABI/-/wikis/uploads/0690db0a3b7e5d8a44e0271a4be54aa7/linux-gABI-and-or-2021-01-13.pdf > >> > > >> > -- > >> > H.J. > >> > >> Here is the binutils patch to implement it. > >> > > > >If there are no objections, I will check it in tomorrow. > > If the use case is just ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA, it'd be > very kind of you if you can collect more use cases before generalizing > this into a non-arch-specific GNU PROPERTY. > > The "copy relocations on protected data symbols" thing is x86 specific > and only applies with gcc+GNU ld+glibc. > Non-x86 architectures don't have this thing. > gold doesn't have this thing. > clang doesn't have this thing.
It will be used to remove copy relocation and implement canonical function pointers, which will benefit protected data and function. -- H.J.
