Avoid using fork() when probing system libstdc++

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>
+
+#define FLAG_ANY                        -1
+#define FLAG_TYPE_MASK                  0x00ff
+#define FLAG_LIBC4                      0x0000
+#define FLAG_ELF                        0x0001
+#define FLAG_ELF_LIBC5                  0x0002
+#define FLAG_ELF_LIBC6                  0x0003
+#define FLAG_REQUIRED_MASK              0xff00
+#define FLAG_SPARC_LIB64                0x0100
+#define FLAG_IA64_LIB64                 0x0200
+#define FLAG_X8664_LIB64                0x0300
+#define FLAG_S390_LIB64                 0x0400
+#define FLAG_POWERPC_LIB64              0x0500
+#define FLAG_MIPS64_LIBN32              0x0600
+#define FLAG_MIPS64_LIBN64              0x0700
+#define FLAG_X8664_LIBX32               0x0800
+#define FLAG_ARM_LIBHF                  0x0900
+#define FLAG_AARCH64_LIB64              0x0a00
+#define FLAG_ARM_LIBSF                  0x0b00
+#define FLAG_MIPS_LIB32_NAN2008         0x0c00
+#define FLAG_MIPS64_LIBN32_NAN2008      0x0d00
+#define FLAG_MIPS64_LIBN64_NAN2008      0x0e00
+#define FLAG_RISCV_FLOAT_ABI_SOFT       0x0f00
+#define FLAG_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
+
+#ifndef LD_SO_CACHE
+# define LD_SO_CACHE SYSCONFDIR "/ld.so.cache"
+#endif
+
+#define CACHEMAGIC "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
+        ...
+*/
+struct file_entry
+{
+  int flags;            /* This is 1 for an ELF library.  */
+  unsigned int key, value; /* String table indices.  */
+};
+
+struct cache_file
+{
+  char magic[sizeof CACHEMAGIC - 1];
+  unsigned int nlibs;
+  struct file_entry libs[0];
+};
+
+#define CACHEMAGIC_NEW "glibc-ld.so.cache"
+#define CACHE_VERSION "1.1"
+#define CACHEMAGIC_VERSION_NEW CACHEMAGIC_NEW CACHE_VERSION
+
+
+struct file_entry_new
+{
+  int32_t flags;                /* This is 1 for an ELF library.  */
+  uint32_t key, value;          /* String table indices.  */
+  uint32_t osversion;           /* Required OS version.  */
+  uint64_t hwcap;               /* Hwcap entry.  */
+};
+
+struct cache_file_new
+{
+  char magic[sizeof CACHEMAGIC_NEW - 1];
+  char version[sizeof CACHE_VERSION - 1];
+  uint32_t nlibs;               /* Number of entries.  */
+  uint32_t len_strings;         /* Size of string table. */
+  uint32_t unused[5];           /* Leave space for future extensions
+                                   and align to 8 byte boundary.  */
+  struct file_entry_new libs[0]; /* Entries describing libraries.  */
+  /* After this the string table of size len_strings is found.  */
+};
+
+/* Used to align cache_file_new.  */
+#define ALIGN_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_DLLEXPORT extern int jl_load_repl(int, char **);
 JL_DLLEXPORT void jl_loader_print_stderr(const char * msg);
 void jl_loader_print_stderr3(const char * msg1, const char * msg2, const char * msg3);
+void *jl_loader_open_via_mmap(const char *filepath, size_t *size);
 static void * lookup_symbol(const void * lib_handle, const char * symbol_name);
+const char *jl_loader_probe_system_library(const char *libname, const char *symbol);
+int jl_loader_locate_symbol(const char *library, const char *symbol);
 
 #ifdef _OS_WINDOWS_
 LPWSTR *CommandLineToArgv(LPWSTR lpCmdLine, int *pNumArgs);