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Avoid using fork() when probing system libstdc++
Rather than relying on the linker to do all of the heavy lifting, this changes our probing technique to directly parse the `ld.so.cache` and `libstdc++.so.6` files. As long as we can expect `ld.so.cache` to be available in `/etc` on all systems, this seems to be a reliable way to locate system libraries on Linux systems. That allows us to avoid `fork()`. For a small application that has just started up `fork()` is no big deal, but it's quite heavy-handed for Julia- as-a-library scenarios where resident memory may already be large. Many soft-embedded targets also do not support fork() well, so it is good for our compatibility to adjust this.
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7 files changed

+4969
-109
lines changed

7 files changed

+4969
-109
lines changed

‎cli/Makefile‎

Lines changed: 11 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -5,7 +5,7 @@ include $(JULIAHOME)/Make.inc
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include $(JULIAHOME)/deps/llvm-ver.make
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8-
HEADERS := $(addprefix $(SRCDIR)/,jl_exports.h loader.h) $(addprefix $(JULIAHOME)/src/,julia_fasttls.h support/platform.h support/dirpath.h jl_exported_data.inc jl_exported_funcs.inc)
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HEADERS := $(addprefix $(SRCDIR)/,jl_exports.h loader.h elf.h dl-cache.h) $(addprefix $(JULIAHOME)/src/,julia_fasttls.h support/platform.h support/dirpath.h jl_exported_data.inc jl_exported_funcs.inc)
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LOADER_CFLAGS = $(JCFLAGS) -I$(BUILDROOT)/src -I$(JULIAHOME)/src -I$(JULIAHOME)/src/support -I$(build_includedir) -ffreestanding
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LOADER_LDFLAGS = $(JLDFLAGS) -ffreestanding -L$(build_shlibdir) -L$(build_libdir)
@@ -41,8 +41,8 @@ endif # MSYS2
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EXE_OBJS := $(BUILDDIR)/loader_exe.o
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EXE_DOBJS := $(BUILDDIR)/loader_exe.dbg.obj
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LIB_OBJS := $(BUILDDIR)/loader_lib.o
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LIB_DOBJS := $(BUILDDIR)/loader_lib.dbg.obj
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LIB_OBJS := $(BUILDDIR)/loader_lib.o $(BUILDDIR)/loader_symbol_probe.o $(BUILDDIR)/loader_library_probe.o
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LIB_DOBJS := $(BUILDDIR)/loader_lib.dbg.obj $(BUILDDIR)/loader_symbol_probe.o $(BUILDDIR)/loader_library_probe.o
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# If this is an architecture that supports dynamic linking, link in a trampoline definition
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ifneq (,$(wildcard $(SRCDIR)/trampolines/trampolines_$(ARCH).S))
@@ -66,6 +66,14 @@ $(BUILDDIR)/loader_trampolines.o : $(SRCDIR)/trampolines/trampolines_$(ARCH).S $
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@$(call PRINT_CC, $(CC) $(SHIPFLAGS) $(LOADER_CFLAGS) $< -c -o $@)
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$(BUILDDIR)/loader_trampolines.dbg.obj : $(SRCDIR)/trampolines/trampolines_$(ARCH).S $(HEADERS) $(SRCDIR)/trampolines/common.h
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@$(call PRINT_CC, $(CC) $(DEBUGFLAGS) $(LOADER_CFLAGS) $< -c -o $@)
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$(BUILDDIR)/loader_library_probe.o : $(SRCDIR)/loader_library_probe.c $(HEADERS) $(JULIAHOME)/VERSION
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@$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(SHIPFLAGS) $(LOADER_CFLAGS) -c $< -o $@)
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$(BUILDDIR)/loader_library_probe.dbg.obj : $(SRCDIR)/loader_library_probe.c $(HEADERS) $(JULIAHOME)/VERSION
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@$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(DEBUGFLAGS) $(LOADER_CFLAGS) -c $< -o $@)
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$(BUILDDIR)/loader_symbol_probe.o : $(SRCDIR)/loader_symbol_probe.c $(HEADERS) $(JULIAHOME)/VERSION
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@$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(SHIPFLAGS) $(LOADER_CFLAGS) -c $< -o $@)
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$(BUILDDIR)/loader_symbol_probe.dbg.obj : $(SRCDIR)/loader_symbol_probe.c $(HEADERS) $(JULIAHOME)/VERSION
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@$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(DEBUGFLAGS) $(LOADER_CFLAGS) -c $< -o $@)
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# Debugging target to help us see what kind of code is being generated for our trampolines
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dump-trampolines: $(SRCDIR)/trampolines/trampolines_$(ARCH).S

‎cli/dl-cache.h‎

Lines changed: 184 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,184 @@
1+
/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
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Copyright (C) 1999-2019 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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#include <stdint.h>
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#define FLAG_ANY -1
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#define FLAG_TYPE_MASK 0x00ff
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#define FLAG_LIBC4 0x0000
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#define FLAG_ELF 0x0001
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#define FLAG_ELF_LIBC5 0x0002
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#define FLAG_ELF_LIBC6 0x0003
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#define FLAG_REQUIRED_MASK 0xff00
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#define FLAG_SPARC_LIB64 0x0100
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#define FLAG_IA64_LIB64 0x0200
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#define FLAG_X8664_LIB64 0x0300
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#define FLAG_S390_LIB64 0x0400
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#define FLAG_POWERPC_LIB64 0x0500
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#define FLAG_MIPS64_LIBN32 0x0600
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#define FLAG_MIPS64_LIBN64 0x0700
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#define FLAG_X8664_LIBX32 0x0800
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#define FLAG_ARM_LIBHF 0x0900
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#define FLAG_AARCH64_LIB64 0x0a00
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#define FLAG_ARM_LIBSF 0x0b00
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#define FLAG_MIPS_LIB32_NAN2008 0x0c00
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#define FLAG_MIPS64_LIBN32_NAN2008 0x0d00
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#define FLAG_MIPS64_LIBN64_NAN2008 0x0e00
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#define FLAG_RISCV_FLOAT_ABI_SOFT 0x0f00
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#define FLAG_RISCV_FLOAT_ABI_DOUBLE 0x1000
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#if defined(_CPU_X86_64_)
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#define _DL_CACHE_DEFAULT_ID 0x303
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#define _dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
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#elif defined(_CPU_AARCH64_)
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#ifdef __LP64__
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# define _DL_CACHE_DEFAULT_ID (FLAG_AARCH64_LIB64 | FLAG_ELF_LIBC6)
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#else
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# define _DL_CACHE_DEFAULT_ID (FLAG_AARCH64_LIB32 | FLAG_ELF_LIBC6)
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#endif
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#define _dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
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#elif defined(_CPU_RISCV64_)
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/* For now we only support the natural XLEN ABI length on all targets, so the
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only bits that need to go into ld.so.cache are the FLEG ABI length. */
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#if defined __riscv_float_abi_double
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# define _DL_CACHE_DEFAULT_ID (FLAG_RISCV_FLOAT_ABI_DOUBLE | FLAG_ELF_LIBC6)
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#else
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# define _DL_CACHE_DEFAULT_ID (FLAG_RISCV_FLOAT_ABI_SOFT | FLAG_ELF_LIBC6)
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#endif
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#define _dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
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#elif defined(_CPU_ARM_)
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/* In order to support the transition from unmarked objects
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to marked objects we must treat unmarked objects as
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compatible with either FLAG_ARM_LIBHF or FLAG_ARM_LIBSF. */
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#ifdef __ARM_PCS_VFP
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# define _dl_cache_check_flags(flags) \
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((flags) == (FLAG_ARM_LIBHF | FLAG_ELF_LIBC6) \
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|| (flags) == FLAG_ELF_LIBC6)
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#else
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# define _dl_cache_check_flags(flags) \
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((flags) == (FLAG_ARM_LIBSF | FLAG_ELF_LIBC6) \
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|| (flags) == FLAG_ELF_LIBC6)
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#endif
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#elif defined(_CPU_X86_)
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/* Defined as (FLAG_ELF_LIBC6 | FLAG_X8664_LIBX32). */
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#undef _DL_CACHE_DEFAULT_ID
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#define _DL_CACHE_DEFAULT_ID 0x803
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#elif defined(_CPU_PPC64_)
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#define _DL_CACHE_DEFAULT_ID 0x503
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#define _dl_cache_check_flags(flags) \
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((flags) == _DL_CACHE_DEFAULT_ID)
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#else
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#error "Missing CPU arch-specific definitions in dl-cache.h"
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#endif
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#ifndef _DL_CACHE_DEFAULT_ID
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# define _DL_CACHE_DEFAULT_ID 3
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#endif
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#ifndef _dl_cache_check_flags
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# define _dl_cache_check_flags(flags) \
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((flags) == 1 || (flags) == _DL_CACHE_DEFAULT_ID)
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#endif
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#ifndef LD_SO_CACHE
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# define LD_SO_CACHE SYSCONFDIR "/ld.so.cache"
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#endif
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#define CACHEMAGIC "ld.so-1.7.0"
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/* libc5 and glibc 2.0/2.1 use the same format. For glibc 2.2 another
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format has been added in a compatible way:
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The beginning of the string table is used for the new table:
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old_magic
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nlibs
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libs[0]
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...
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libs[nlibs-1]
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pad, new magic needs to be aligned
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- this is string[0] for the old format
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new magic - this is string[0] for the new format
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newnlibs
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...
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newlibs[0]
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...
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newlibs[newnlibs-1]
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string 1
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string 2
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...
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*/
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struct file_entry
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{
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int flags; /* This is 1 for an ELF library. */
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unsigned int key, value; /* String table indices. */
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};
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struct cache_file
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{
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char magic[sizeof CACHEMAGIC - 1];
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unsigned int nlibs;
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struct file_entry libs[0];
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};
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#define CACHEMAGIC_NEW "glibc-ld.so.cache"
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#define CACHE_VERSION "1.1"
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#define CACHEMAGIC_VERSION_NEW CACHEMAGIC_NEW CACHE_VERSION
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struct file_entry_new
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{
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int32_t flags; /* This is 1 for an ELF library. */
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uint32_t key, value; /* String table indices. */
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uint32_t osversion; /* Required OS version. */
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uint64_t hwcap; /* Hwcap entry. */
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};
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struct cache_file_new
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{
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char magic[sizeof CACHEMAGIC_NEW - 1];
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char version[sizeof CACHE_VERSION - 1];
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uint32_t nlibs; /* Number of entries. */
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uint32_t len_strings; /* Size of string table. */
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uint32_t unused[5]; /* Leave space for future extensions
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and align to 8 byte boundary. */
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struct file_entry_new libs[0]; /* Entries describing libraries. */
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/* After this the string table of size len_strings is found. */
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};
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/* Used to align cache_file_new. */
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#define ALIGN_CACHE(addr) \
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(((addr) + __alignof__ (struct cache_file_new) -1) \
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& (~(__alignof__ (struct cache_file_new) - 1)))
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// extern int _dl_cache_libcmp (const char *p1, const char *p2) attribute_hidden;

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