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This patch adds support for the ELFv2 ABI feature to remove function descriptors. See this GCC patch for in-depth discussion: http://gcc.gnu.org/ml/gcc-patches/2013-11/msg01141.html This mostly involves two types of changes: updating assembler source files to the new logic, and updating the dynamic loader. After the refactoring in the previous patch, most of the assembler source changes can be handled simply by providing ELFv2 versions of the macros in sysdep.h. One somewhat non-obvious change is in __GI__setjmp: this used to "fall through" to the immediately following __setjmp ENTRY point. This is no longer safe in the ELFv2 since ENTRY defines both a global and a local entry point, and you cannot simply fall through to a global entry point as it requires r12 to be set up. Also, makecontext needs to be updated to set up registers according to the new ABI for calling into the context's start routine. The dynamic linker changes mostly consist of removing special code to handle function descriptors. We also need to support the new PLT and glink format used by the the ELFv2 linker, see: https://sourceware.org/ml/binutils/2013-10/msg00376.html In addition, the dynamic linker now verifies that the dynamic libraries it loads match its own ABI. The hack in VDSO_IFUNC_RET to "synthesize" a function descriptor for vDSO routines is also no longer necessary for ELFv2.
77 lines
3.1 KiB
C
77 lines
3.1 KiB
C
/* Resolve function pointers to VDSO functions.
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Copyright (C) 2005-2013 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _LIBC_VDSO_H
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#define _LIBC_VDSO_H
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#ifdef SHARED
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extern void *__vdso_gettimeofday attribute_hidden;
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extern void *__vdso_clock_gettime;
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extern void *__vdso_clock_getres;
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extern void *__vdso_get_tbfreq;
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extern void *__vdso_getcpu;
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extern void *__vdso_time;
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#if defined(__PPC64__) || defined(__powerpc64__)
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extern void *__vdso_sigtramp_rt64;
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#else
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extern void *__vdso_sigtramp32;
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extern void *__vdso_sigtramp_rt32;
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#endif
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#if (defined(__PPC64__) || defined(__powerpc64__)) && _CALL_ELF != 2
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/* The correct solution is for _dl_vdso_vsym to return the address of the OPD
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for the kernel VDSO function. That address would then be stored in the
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__vdso_* variables and returned as the result of the IFUNC resolver function.
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Yet, the kernel does not contain any OPD entries for the VDSO functions
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(incomplete implementation). However, PLT relocations for IFUNCs still expect
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the address of an OPD to be returned from the IFUNC resolver function (since
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PLT entries on PPC64 are just copies of OPDs). The solution for now is to
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create an artificial static OPD for each VDSO function returned by a resolver
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function. The TOC value is set to a non-zero value to avoid triggering lazy
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symbol resolution via .glink0/.plt0 for a zero TOC (requires thread-safe PLT
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sequences) when the dynamic linker isn't prepared for it e.g. RTLD_NOW. None
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of the kernel VDSO routines use the TOC or AUX values so any non-zero value
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will work. Note that function pointer comparisons will not use this artificial
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static OPD since those are resolved via ADDR64 relocations and will point at
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the non-IFUNC default OPD for the symbol. Lastly, because the IFUNC relocations
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are processed immediately at startup the resolver functions and this code need
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not be thread-safe, but if the caller writes to a PLT slot it must do so in a
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thread-safe manner with all the required barriers. */
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#define VDSO_IFUNC_RET(value) \
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({ \
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static Elf64_FuncDesc vdso_opd = { .fd_toc = ~0x0 }; \
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vdso_opd.fd_func = (Elf64_Addr)value; \
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&vdso_opd; \
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})
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#else
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#define VDSO_IFUNC_RET(value) ((void *) (value))
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#endif
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#endif
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#endif /* _LIBC_VDSO_H */
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