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035c012e32
It turns out the startup code in csu/elf-init.c has a perfect pair of ROP gadgets (see Marco-Gisbert and Ripoll-Ripoll, "return-to-csu: A New Method to Bypass 64-bit Linux ASLR"). These functions are not needed in dynamically-linked binaries because DT_INIT/DT_INIT_ARRAY are already processed by the dynamic linker. However, the dynamic linker skipped the main program for some reason. For maximum backwards compatibility, this is not changed, and instead, the main map is consulted from __libc_start_main if the init function argument is a NULL pointer. For statically linked binaries, the old approach based on linker symbols is still used because there is nothing else available. A new symbol version __libc_start_main@@GLIBC_2.34 is introduced because new binaries running on an old libc would not run their ELF constructors, leading to difficult-to-debug issues.
186 lines
6.7 KiB
Makefile
186 lines
6.7 KiB
Makefile
# Makefile for csu code for GNU C library.
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# Copyright (C) 1995-2021 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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# <https://www.gnu.org/licenses/>.
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# This directory contains the C startup code (that which calls main). This
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# consists of the startfile, built from start.c and installed as crt0.o
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# (traditionally) or crt1.o (for ELF). In ELF we also install crti.o and
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# crtn.o, special "initializer" and "finalizer" files used in the link
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# to make the .init and .fini sections work right.
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subdir := csu
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include ../Makeconfig
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routines = init-first libc-start $(libc-init) sysdep version check_fds \
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libc-tls dso_handle
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aux = errno
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elide-routines.os = libc-tls
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csu-dummies = $(filter-out $(start-installed-name),crt1.o Mcrt1.o)
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extra-objs = start.o \
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$(start-installed-name) g$(start-installed-name) $(csu-dummies) \
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S$(start-installed-name)
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omit-deps = $(patsubst %.o,%,$(start-installed-name) g$(start-installed-name) \
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b$(start-installed-name) $(csu-dummies) \
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S$(start-installed-name) \
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r$(start-installed-name) \
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gr$(start-installed-name))
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install-lib = $(start-installed-name) g$(start-installed-name) $(csu-dummies)
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# No tests are allowed in the csu/ subdirectory because the startup
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# code is compiled with special flags.
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tests =
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CFLAGS-.o += $(no-stack-protector)
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CFLAGS-.op += $(no-stack-protector)
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CFLAGS-.os += $(no-stack-protector)
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# Dummy object not actually used for anything. It is linked into
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# crt1.o nevertheless, which in turn is statically linked into
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# applications, so that build flags matter.
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# See <https://sourceware.org/ml/libc-alpha/2018-07/msg00101.html>.
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# NB: Using $(stack-protector) in this way causes a wrong definition
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# STACK_PROTECTOR_LEVEL due to the preceding $(no-stack-protector),
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# but it does not matter for this source file.
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CFLAGS-static-reloc.os += $(stack-protector)
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ifeq (yes,$(build-shared))
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extra-objs += S$(start-installed-name) gmon-start.os
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ifneq ($(start-installed-name),$(static-start-installed-name))
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extra-objs += gmon-start.o
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endif
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install-lib += S$(start-installed-name)
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generated += start.os
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else
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extra-objs += gmon-start.o
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endif
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ifneq ($(start-installed-name),$(static-start-installed-name))
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# FIXME: Only Hurd defines static-start-installed-name. Hurd needs to
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# provide special rules to support static PIE.
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extra-objs += $(static-start-installed-name) g$(static-start-installed-name)
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omit-deps += $(patsubst %.o,%,$(static-start-installed-name) \
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g$(static-start-installed-name))
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install-lib += $(static-start-installed-name) g$(static-start-installed-name)
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else
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ifeq (yes,$(enable-static-pie))
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extra-objs += r$(start-installed-name) gr$(start-installed-name)
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install-lib += r$(start-installed-name) gr$(start-installed-name)
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endif
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endif
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before-compile += $(objpfx)abi-tag.h
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generated += abi-tag.h
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# These are the special initializer/finalizer files. They are always the
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# first and last file in the link. crti.o ... crtn.o define the global
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# "functions" _init and _fini to run the .init and .fini sections.
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crtstuff = crti crtn
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install-lib += $(crtstuff:=.o)
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extra-objs += $(crtstuff:=.o)
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ifneq ($(multidir),.)
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multilib-extra-objs = $(addprefix $(multidir)/, $(install-lib))
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extra-objs += $(multilib-extra-objs)
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endif
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extra-objs += abi-note.o init.o static-reloc.o
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ifeq (yes,$(build-shared))
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extra-objs += static-reloc.os
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endif
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asm-CPPFLAGS += -I$(objpfx).
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# Enable unwinding so backtrace unwinds to __libc_start_main
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CFLAGS-libc-start.c += -funwind-tables
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include ../Rules
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# Make these in the lib pass so they're available in time to link things with.
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subdir_lib: $(extra-objs:%=$(objpfx)%)
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define link-relocatable
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$(CC) -nostdlib -nostartfiles -r -o $@ $^
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endef
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ifndef start-installed-name-rule
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# We link the ELF startfile along with a SHT_NOTE section indicating
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# the kernel ABI the binaries linked with this library will require.
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$(objpfx)$(start-installed-name): $(objpfx)start.o $(objpfx)abi-note.o \
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$(objpfx)init.o $(objpfx)static-reloc.o
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$(link-relocatable)
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$(objpfx)r$(start-installed-name): $(objpfx)start.o $(objpfx)abi-note.o \
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$(objpfx)init.o
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$(link-relocatable)
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$(objpfx)S$(start-installed-name): $(objpfx)start.os $(objpfx)abi-note.o \
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$(objpfx)init.o
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$(link-relocatable)
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endif
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# The profiling startfile is made by linking together the normal
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# startfile with gmon-start.o, which defines a constructor function
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# to turn on profiling code at startup.
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ifeq (yes,$(build-shared))
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$(objpfx)g$(start-installed-name): \
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$(objpfx)g%: $(objpfx)S% $(objpfx)gmon-start.os $(objpfx)static-reloc.os
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$(link-relocatable)
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$(objpfx)gr$(start-installed-name): \
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$(objpfx)gr%: $(objpfx)r% $(objpfx)gmon-start.o
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$(link-relocatable)
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ifneq ($(start-installed-name),$(static-start-installed-name))
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$(objpfx)g$(static-start-installed-name): \
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$(objpfx)g%: $(objpfx)% $(objpfx)gmon-start.o
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$(link-relocatable)
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endif
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else
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$(addprefix $(objpfx),$(sort g$(start-installed-name) \
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g$(static-start-installed-name))): \
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$(objpfx)g%: $(objpfx)% $(objpfx)gmon-start.o
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$(link-relocatable)
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endif
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# These extra files are sometimes expected by system standard linking
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# procedures, but we have nothing for them to do. So compile empty files.
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$(addprefix $(objpfx),$(filter-out $(start-installed-name), $(csu-dummies))):\
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$(before-compile)
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$(COMPILE.c) -o $@ -x c /dev/null
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# These headers are used by the startup code.
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$(objpfx)abi-tag.h: $(..)abi-tags
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$(make-target-directory)
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rm -f $@.new
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sed -e 's/#.*$$//' -e '/^[ ]*$$/d' $< | \
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while read conf tagos tagver; do \
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test `expr '$(config-machine)-$(config-vendor)-$(config-os)' \
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: "$$conf"` != 0 || continue; \
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( echo "$$tagos" | \
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sed -e 's/[^0-9xXa-fA-F ]//' \
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-e 's/^/#define __ABI_TAG_OS /'; \
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echo "#ifndef __ABI_TAG_VERSION"; \
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echo "$$tagver" | \
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sed -e 's/[^0-9xXa-fA-F]/ /g' -e 's/ *$$//' \
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-e 's/ /,/g' -e 's/^/# define __ABI_TAG_VERSION /'; \
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echo "#endif" ) > $@.new; \
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done
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if test -r $@.new; then mv -f $@.new $@; \
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else echo >&2 'This configuration not matched in $<'; exit 1; fi
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ifneq ($(multidir),.)
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$(addprefix $(objpfx)$(multidir)/, $(install-lib)): $(addprefix $(objpfx), $(install-lib))
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$(make-link-multidir)
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endif
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