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.

Author: topolarity

THIRDPARTY.md

@@ -4,6 +4,7 @@ and some utilities (most of the rest of the files in this repository). See below
 for exceptions.
 
 -[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)].
+-[dl-cache.h](https://www.gnu.org/licenses/old-licenses/lgpl-2.1.html) (for reading ld-cache files on startup) [LGPL2.1+]
 -[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.
 -[LLVM](https://releases.llvm.org/3.9.0/LICENSE.TXT) (for parts of src/disasm.cpp) [UIUC]
 -[NetBSD](https://www.netbsd.org/about/redistribution.html) (for setjmp, longjmp, and strptime implementations on Windows) [BSD-3]

cli/Makefile

@@ -5,7 +5,7 @@ include $(JULIAHOME)/Make.inc
 include$(JULIAHOME)/deps/llvm-ver.make
 
 
-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)
+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)
 
 LOADER_CFLAGS = $(JCFLAGS) -I$(BUILDROOT)/src -I$(JULIAHOME)/src -I$(JULIAHOME)/src/support -I$(build_includedir) -ffreestanding
 LOADER_LDFLAGS = $(JLDFLAGS) -ffreestanding -L$(build_shlibdir) -L$(build_libdir)
@@ -46,8 +46,8 @@ endif # USE_RT_STATIC_LIBSTDCXX
 
 EXE_OBJS := $(BUILDDIR)/loader_exe.o
 EXE_DOBJS := $(BUILDDIR)/loader_exe.dbg.obj
-LIB_OBJS := $(BUILDDIR)/loader_lib.o
-LIB_DOBJS := $(BUILDDIR)/loader_lib.dbg.obj
+LIB_OBJS := $(BUILDDIR)/loader_lib.o$(BUILDDIR)/loader_symbol_probe.o $(BUILDDIR)/loader_library_probe.o
+LIB_DOBJS := $(BUILDDIR)/loader_lib.dbg.obj$(BUILDDIR)/loader_symbol_probe.dbg.obj $(BUILDDIR)/loader_library_probe.dbg.obj
 
 # If this is an architecture that supports dynamic linking, link in a trampoline definition
 ifneq (,$(wildcard$(SRCDIR)/trampolines/trampolines_$(ARCH).S))
@@ -71,6 +71,14 @@ $(BUILDDIR)/loader_trampolines.o : $(SRCDIR)/trampolines/trampolines_$(ARCH).S $
  @$(call PRINT_CC, $(CC)$(SHIPFLAGS)$(LOADER_CFLAGS)$< -c -o $@)
 $(BUILDDIR)/loader_trampolines.dbg.obj : $(SRCDIR)/trampolines/trampolines_$(ARCH).S $(HEADERS)$(SRCDIR)/trampolines/common.h
  @$(call PRINT_CC, $(CC)$(DEBUGFLAGS)$(LOADER_CFLAGS)$< -c -o $@)
+$(BUILDDIR)/loader_library_probe.o : $(SRCDIR)/loader_library_probe.c $(HEADERS)$(JULIAHOME)/VERSION
+ @$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(SHIPFLAGS)$(LOADER_CFLAGS) -c $< -o $@)
+$(BUILDDIR)/loader_library_probe.dbg.obj : $(SRCDIR)/loader_library_probe.c $(HEADERS)$(JULIAHOME)/VERSION
+ @$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(DEBUGFLAGS)$(LOADER_CFLAGS) -c $< -o $@)
+$(BUILDDIR)/loader_symbol_probe.o : $(SRCDIR)/loader_symbol_probe.c $(HEADERS)$(JULIAHOME)/VERSION
+ @$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(SHIPFLAGS)$(LOADER_CFLAGS) -c $< -o $@)
+$(BUILDDIR)/loader_symbol_probe.dbg.obj : $(SRCDIR)/loader_symbol_probe.c $(HEADERS)$(JULIAHOME)/VERSION
+ @$(call PRINT_CC, $(CC) -DJL_LIBRARY_EXPORTS $(DEBUGFLAGS)$(LOADER_CFLAGS) -c $< -o $@)
 
 # Debugging target to help us see what kind of code is being generated for our trampolines
 dump-trampolines: $(SRCDIR)/trampolines/trampolines_$(ARCH).S

cli/dl-cache.h

@@ -0,0 +1,184 @@
+/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
+ Copyright (C) 1999-2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include<stdint.h>
+
+#defineFLAG_ANY -1
+#defineFLAG_TYPE_MASK 0x00ff
+#defineFLAG_LIBC4 0x0000
+#defineFLAG_ELF 0x0001
+#defineFLAG_ELF_LIBC5 0x0002
+#defineFLAG_ELF_LIBC6 0x0003
+#defineFLAG_REQUIRED_MASK 0xff00
+#defineFLAG_SPARC_LIB64 0x0100
+#defineFLAG_IA64_LIB64 0x0200
+#defineFLAG_X8664_LIB64 0x0300
+#defineFLAG_S390_LIB64 0x0400
+#defineFLAG_POWERPC_LIB64 0x0500
+#defineFLAG_MIPS64_LIBN32 0x0600
+#defineFLAG_MIPS64_LIBN64 0x0700
+#defineFLAG_X8664_LIBX32 0x0800
+#defineFLAG_ARM_LIBHF 0x0900
+#defineFLAG_AARCH64_LIB64 0x0a00
+#defineFLAG_ARM_LIBSF 0x0b00
+#defineFLAG_MIPS_LIB32_NAN2008 0x0c00
+#defineFLAG_MIPS64_LIBN32_NAN2008 0x0d00
+#defineFLAG_MIPS64_LIBN64_NAN2008 0x0e00
+#defineFLAG_RISCV_FLOAT_ABI_SOFT 0x0f00
+#defineFLAG_RISCV_FLOAT_ABI_DOUBLE 0x1000
+
+#if defined(_CPU_X86_64_)
+
+#define_DL_CACHE_DEFAULT_ID 0x303
+#define_dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
+
+#elif defined(_CPU_AARCH64_)
+
+#ifdef__LP64__
+# define_DL_CACHE_DEFAULT_ID (FLAG_AARCH64_LIB64 | FLAG_ELF_LIBC6)
+#else
+# define_DL_CACHE_DEFAULT_ID (FLAG_AARCH64_LIB32 | FLAG_ELF_LIBC6)
+#endif
+
+#define_dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
+
+#elif defined(_CPU_RISCV64_)
+
+/* For now we only support the natural XLEN ABI length on all targets, so the
+ only bits that need to go into ld.so.cache are the flags for ABI length. */
+#if defined __riscv_float_abi_double
+# define_DL_CACHE_DEFAULT_ID (FLAG_RISCV_FLOAT_ABI_DOUBLE | FLAG_ELF_LIBC6)
+#else
+# define_DL_CACHE_DEFAULT_ID (FLAG_RISCV_FLOAT_ABI_SOFT | FLAG_ELF_LIBC6)
+#endif
+
+#define_dl_cache_check_flags(flags) ((flags) == _DL_CACHE_DEFAULT_ID)
+
+#elif defined(_CPU_ARM_)
+
+/* In order to support the transition from unmarked objects
+ to marked objects we must treat unmarked objects as
+ compatible with either FLAG_ARM_LIBHF or FLAG_ARM_LIBSF. */
+#ifdef__ARM_PCS_VFP
+# define_dl_cache_check_flags(flags) \
+ ((flags) == (FLAG_ARM_LIBHF | FLAG_ELF_LIBC6) \
+ || (flags) == FLAG_ELF_LIBC6)
+#else
+# define_dl_cache_check_flags(flags) \
+ ((flags) == (FLAG_ARM_LIBSF | FLAG_ELF_LIBC6) \
+ || (flags) == FLAG_ELF_LIBC6)
+#endif
+
+#elif defined(_CPU_X86_)
+
+/* Defined as (FLAG_ELF_LIBC6 | FLAG_X8664_LIBX32). */
+#undef _DL_CACHE_DEFAULT_ID
+#define_DL_CACHE_DEFAULT_ID 0x803
+
+#elif defined(_CPU_PPC64_)
+
+#define_DL_CACHE_DEFAULT_ID 0x503
+
+#define_dl_cache_check_flags(flags) \
+ ((flags) == _DL_CACHE_DEFAULT_ID)
+
+#else
+
+#error "Missing CPU arch-specific definitions in dl-cache.h"
+
+#endif
+
+#ifndef_DL_CACHE_DEFAULT_ID
+# define_DL_CACHE_DEFAULT_ID 3
+#endif
+
+#ifndef_dl_cache_check_flags
+# define_dl_cache_check_flags(flags) \
+ ((flags) == 1 || (flags) == _DL_CACHE_DEFAULT_ID)
+#endif
+
+#ifndefLD_SO_CACHE
+# defineLD_SO_CACHE SYSCONFDIR "/ld.so.cache"
+#endif
+
+#defineCACHEMAGIC "ld.so-1.7.0"
+
+/* libc5 and glibc 2.0/2.1 use the same format. For glibc 2.2 another
+ format has been added in a compatible way:
+ The beginning of the string table is used for the new table:
+ old_magic
+ nlibs
+ libs[0]
+ ...
+ libs[nlibs-1]
+ pad, new magic needs to be aligned
+ - this is string[0] for the old format
+ new magic - this is string[0] for the new format
+ newnlibs
+ ...
+ newlibs[0]
+ ...
+ newlibs[newnlibs-1]
+ string 1
+ string 2
+ ...
+*/
+structfile_entry
+{
+intflags; /* This is 1 for an ELF library. */
+unsigned intkey, value; /* String table indices. */
+};
+
+structcache_file
+{
+charmagic[sizeofCACHEMAGIC-1];
+unsigned intnlibs;
+structfile_entrylibs[0];
+};
+
+#defineCACHEMAGIC_NEW "glibc-ld.so.cache"
+#defineCACHE_VERSION "1.1"
+#defineCACHEMAGIC_VERSION_NEW CACHEMAGIC_NEW CACHE_VERSION
+
+
+structfile_entry_new
+{
+int32_tflags; /* This is 1 for an ELF library. */
+uint32_tkey, value; /* String table indices. */
+uint32_tosversion; /* Required OS version. */
+uint64_thwcap; /* Hwcap entry. */
+};
+
+structcache_file_new
+{
+charmagic[sizeofCACHEMAGIC_NEW-1];
+charversion[sizeofCACHE_VERSION-1];
+uint32_tnlibs; /* Number of entries. */
+uint32_tlen_strings; /* Size of string table. */
+uint32_tunused[5]; /* Leave space for future extensions
+ and align to 8 byte boundary. */
+structfile_entry_newlibs[0]; /* Entries describing libraries. */
+/* After this the string table of size len_strings is found. */
+};
+
+/* Used to align cache_file_new. */
+#defineALIGN_CACHE(addr) \
+(((addr) + __alignof__ (struct cache_file_new) -1) \
+ & (~(__alignof__ (struct cache_file_new) - 1)))
+
+// extern int _dl_cache_libcmp (const char *p1, const char *p2) attribute_hidden;

cli/loader.h

@@ -70,7 +70,10 @@
 JL_DLLEXPORTexternintjl_load_repl(int, char**);
 JL_DLLEXPORTvoidjl_loader_print_stderr(constchar*msg);
 voidjl_loader_print_stderr3(constchar*msg1, constchar*msg2, constchar*msg3);
+void*jl_loader_open_via_mmap(constchar*filepath, size_t*size);
 staticvoid*lookup_symbol(constvoid*lib_handle, constchar*symbol_name);
+constchar*jl_loader_probe_system_library(constchar*libname, constchar*symbol);
+intjl_loader_locate_symbol(constchar*library, constchar*symbol);
 
 #ifdef_OS_WINDOWS_
 LPWSTR*CommandLineToArgv(LPWSTRlpCmdLine, int*pNumArgs);