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Avoid using fork() when probing system libstdc++ (#60254)
Somewhat of a companion to #60248. For a small application that has just started up `fork()` is not a huge concern, 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. Rather than relying on the linker to do all of the heavy lifting, this changes our `libstdcxx` probe sequence to directly parse the `ld.so.cache` and `libstdc++.so.6` files. As long as we can expect `/etc/ld.so.cache` to be the same path on all Linux systems, this seems to be a reliable way to locate system libraries. (cherry picked from commit ac4ee59)
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‎THIRDPARTY.md‎

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@@ -4,6 +4,7 @@ and some utilities (most of the rest of the files in this repository). See below
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for exceptions.
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- [crc32c.c](https://stackoverflow.com/questions/17645167/implementing-sse-4-2s-crc32c-in-software) (CRC-32c checksum code by Mark Adler) [[ZLib](https://opensource.org/licenses/Zlib)].
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- [dl-cache.h](https://www.gnu.org/licenses/old-licenses/lgpl-2.1.html) (for reading ld-cache files on startup) [LGPL2.1+]
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- [LDC](https://github.com/ldc-developers/ldc/blob/master/LICENSE) (for ccall/cfunction ABI definitions) [BSD-3]. The portion of code that Julia uses from LDC is [BSD-3] licensed.
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- [LLVM](https://releases.llvm.org/3.9.0/LICENSE.TXT) (for parts of src/disasm.cpp) [UIUC]
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- [NetBSD](https://www.netbsd.org/about/redistribution.html) (for setjmp, longjmp, and strptime implementations on Windows) [BSD-3]

‎cli/Makefile‎

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@@ -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 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)
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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.dbg.obj $(BUILDDIR)/loader_library_probe.dbg.obj
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# If this is an architecture that supports dynamic linking, link in a trampoline definition
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ifneq (,$(wildcard $(SRCDIR)/trampolines/trampolines_$(ARCH).S))
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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

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/* 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 flags for 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;

‎cli/loader.h‎

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JL_DLLEXPORT extern int jl_load_repl(int, char **);
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JL_DLLEXPORT void jl_loader_print_stderr(const char * msg);
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void jl_loader_print_stderr3(const char * msg1, const char * msg2, const char * msg3);
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void *jl_loader_open_via_mmap(const char *filepath, size_t *size);
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static void * lookup_symbol(const void * lib_handle, const char * symbol_name);
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const char *jl_loader_probe_system_library(const char *libname, const char *symbol);
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int jl_loader_locate_symbol(const char *library, const char *symbol);
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#ifdef _OS_WINDOWS_
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LPWSTR *CommandLineToArgv(LPWSTR lpCmdLine, int *pNumArgs);

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