[build] Don't define special symbols in rodso.ld
This changes rodso.ld so its only effect is to produce the
desired optimal layout. It no longer defines special symbols for
use by scripts/gen-rodso-code.sh. (The rodso.ld layout is now what
will become the default for lld with -z rodynamic for these cases
once some corner case issues are resolved in lld.)
Instead, scripts/gen-rodso-code.sh is slightly reworked to glean
the values for the CODE_{START,END} and DATA_{START,END}_dynsym
constants from ELF program and section headers rather than from
symbol values defined by the linker script. userboot's generated
linker script for vDSO access uses linker-script arithmetic to
align the value from the linker's built-in _end symbol rather
than relying on a CODE_END symbol being defined by rodso.ld.
Change-Id: I200b687824c36ec3bd9e7d9d2a25464727ba09ee
Esse commit está contido em:
Roland McGrath
@@ -26,7 +26,8 @@ MODULE_SRCDEPS += $(BUILDDIR)/$(LOCAL_DIR)/userboot-code.h
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$(BUILDDIR)/$(LOCAL_DIR)/userboot-code.h: scripts/gen-rodso-code.sh $(userboot-filename)
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@$(MKDIR)
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$(call BUILDECHO,generating $@)
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$(NOECHO)$(SHELLEXEC) $< '$(NM)' $@.new USERBOOT $(userboot-filename)
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$(NOECHO)$(SHELLEXEC) $< '$(NM)' '$(READELF)' \
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$@.new USERBOOT $(userboot-filename)
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@mv -f $@.new $@
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GENERATED += $(BUILDDIR)/$(LOCAL_DIR)/userboot-code.h
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MODULE_COMPILEFLAGS += -I$(BUILDDIR)/$(LOCAL_DIR)
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@@ -27,7 +27,8 @@ MODULE_SRCDEPS += $(BUILDDIR)/$(LOCAL_DIR)/vdso-code.h
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$(BUILDDIR)/$(LOCAL_DIR)/vdso-code.h: scripts/gen-rodso-code.sh $(vdso-filename)
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@$(MKDIR)
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$(call BUILDECHO,generating $@)
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$(NOECHO)$(SHELLEXEC) $< '$(NM)' $@.new VDSO $(vdso-filename)
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$(NOECHO)$(SHELLEXEC) $< '$(NM)' '$(READELF)' \
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$@.new VDSO $(vdso-filename)
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@mv -f $@.new $@
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GENERATED += $(BUILDDIR)/$(LOCAL_DIR)/vdso-code.h
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MODULE_COMPILEFLAGS += -I$(BUILDDIR)/$(LOCAL_DIR)
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+2
-2
@@ -535,7 +535,7 @@ ifeq ($(call TOBOOL,$(USE_CLANG)),true)
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CC := $(CLANG_TOOLCHAIN_PREFIX)clang
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AR := $(CLANG_TOOLCHAIN_PREFIX)llvm-ar
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OBJDUMP := $(CLANG_TOOLCHAIN_PREFIX)llvm-objdump
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READELF := $(CLANG_TOOLCHAIN_PREFIX)llvm-readobj -elf-output-style=GNU
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READELF := $(CLANG_TOOLCHAIN_PREFIX)llvm-readelf
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CPPFILT := $(CLANG_TOOLCHAIN_PREFIX)llvm-cxxfilt
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SIZE := $(CLANG_TOOLCHAIN_PREFIX)llvm-size
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NM := $(CLANG_TOOLCHAIN_PREFIX)llvm-nm
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@@ -597,7 +597,7 @@ HOST_CC := $(HOST_TOOLCHAIN_PREFIX)clang
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HOST_CXX := $(HOST_TOOLCHAIN_PREFIX)clang++
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HOST_AR := $(HOST_TOOLCHAIN_PREFIX)llvm-ar
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HOST_OBJDUMP := $(HOST_TOOLCHAIN_PREFIX)llvm-objdump
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HOST_READELF := $(HOST_TOOLCHAIN_PREFIX)llvm-readobj
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HOST_READELF := $(HOST_TOOLCHAIN_PREFIX)llvm-readelf
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HOST_CPPFILT := $(HOST_TOOLCHAIN_PREFIX)llvm-cxxfilt
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HOST_SIZE := $(HOST_TOOLCHAIN_PREFIX)llvm-size
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HOST_NM := $(HOST_TOOLCHAIN_PREFIX)llvm-nm
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@@ -17,7 +17,7 @@
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# of entries in the table.
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usage() {
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echo >&2 "Usage: $0 NM OUTFILE {NAME DSO}..."
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echo >&2 "Usage: $0 NM READELF OUTFILE {NAME DSO}..."
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exit 2
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}
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@@ -27,14 +27,14 @@ fi
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NM="$1"
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shift
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READELF="$1"
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shift
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OUTFILE="$1"
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shift
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if [ "$(basename $0)" = "sh" ]
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then
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set -e
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else
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set -o pipefail -e
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set -e
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if [ -n "$BASH_VERSION" ]; then
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set -o pipefail
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fi
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grok_code_symbols() {
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@@ -78,12 +78,72 @@ find_dynsym_slots() {
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"$NM" -P -D -p "$2" | grok_dynsym_slots "$1"
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}
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SEGMENTS_HAVE_DYNSYM=22
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SEGMENTS_NO_DYNSYM=33
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grok_segments() {
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local line
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local status=$SEGMENTS_NO_DYNSYM
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while read line; do
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case "$line" in
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# Program header for the code segment, e.g.:
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# LOAD 0x002000 0x0000000000002000 0x0000000000002000 0x00f50f 0x00f50f R E 0x1000
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# ^^^^^ vaddr ^^^^^^ ^filesz^
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*LOAD*\ R\ E\ *)
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local words=($line)
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local vaddr=$(printf '%#x' ${words[2]})
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local filesz=$(printf '%#x' ${words[4]})
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echo "#define ${1}_CODE_START $vaddr" >> $OUTFILE
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echo "#define ${1}_CODE_END (((${1}_CODE_START + $filesz + (1 << PAGE_SIZE_SHIFT) - 1) >> PAGE_SIZE_SHIFT) << PAGE_SIZE_SHIFT)" >> $OUTFILE
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;;
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# Make sure there's no writable segment.
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*LOAD*W*)
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echo >&2 "$0: writable segment: $line"
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exit 1
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;;
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# Section header for .dynsym, e.g.:
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# [ 3] .dynsym DYNSYM 0000000000001268 001268 000018 18 A 6 1 8
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# ^^^^^ addr ^^^^^ ^size^ ^entsize^
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*DYNSYM*)
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line="${line#*DYNSYM}"
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local words=($line)
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local addr=$(printf '%#x' 0x${words[0]})
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local size=$(printf '%#x' 0x${words[2]})
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local entsize=$(printf '%#x' 0x${words[3]})
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# A dummy .dynsym has a single entry. Don't count that case.
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if [ $size != $entsize ]; then
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status=$SEGMENTS_HAVE_DYNSYM
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echo "#define ${1}_DATA_START_dynsym $addr" >> $OUTFILE
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echo "#define ${1}_DATA_END_dynsym (${1}_DATA_START_dynsym + $size)" >> $OUTFILE
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fi
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;;
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esac
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done
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return $status
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}
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find_segments() {
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# This if silliness disarms -e so we can observe grok_segments's return code.
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if {
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"$READELF" -W -S -l "$2" | grok_segments "$1"
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case $? in
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$SEGMENTS_NO_DYNSYM) have_dynsym=no ;;
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$SEGMENTS_HAVE_DYNSYM) have_dynsym=yes ;;
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*) exit $? ;;
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esac
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return 0
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}; then : ; fi
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}
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while [ $# -gt 0 ]; do
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if [ $# -lt 2 ]; then
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usage
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fi
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echo "#define ${1}_FILENAME \"${2}\"" > $OUTFILE
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find_segments "$1" "$2"
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find_code_symbols "$1" "$2"
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find_dynsym_slots "$1" "$2"
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if [ $have_dynsym = yes ]; then
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find_dynsym_slots "$1" "$2"
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fi
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shift 2
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done
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+1
-7
@@ -62,11 +62,7 @@ SECTIONS {
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*(.hash)
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} :rodata
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.gnu.hash : { *(.gnu.hash) }
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.dynsym : {
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HIDDEN(DATA_START_dynsym = .);
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*(.dynsym)
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HIDDEN(DATA_END_dynsym = .);
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}
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.dynsym : { *(.dynsym) }
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.dynstr : { *(.dynstr) }
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.rodata : {
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@@ -108,7 +104,6 @@ SECTIONS {
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"rodso code must avoid writable data sections!")
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. = ALIGN(CONSTANT(MAXPAGESIZE));
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HIDDEN(CODE_START = .);
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.text : {
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*(.text.unlikely .text.*_unlikely .text.unlikely.*)
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@@ -129,7 +124,6 @@ SECTIONS {
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* (.shstrtab, section headers, .symtab if not stripped, etc.).
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*/
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. = ALIGN(CONSTANT(MAXPAGESIZE));
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HIDDEN(CODE_END = .);
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} :code
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}
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@@ -4,13 +4,14 @@
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// For each function in the vDSO ABI, define a symbol in the linker script
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// pointing to its address. The vDSO is loaded immediately after the
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// userboot DSO image's last page, which is marked by the CODE_END symbol.
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// So these symbols tell the linker where each vDSO function will be found
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// at runtime. The userboot code uses normal calls to these, declared as
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// have hidden visibility so they won't generate PLT entries. This results
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// in the userboot binary having simple PC-relative calls to addresses
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// outside its own image, to where the vDSO will be found at runtime.
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// userboot DSO image's last page, which is found by aligning the magic
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// symbol _end (generated by the linker) up to the next page boundary. So
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// these symbols tell the linker where each vDSO function will be found at
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// runtime. The userboot code uses normal calls to these, declared as have
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// hidden visibility so they won't generate PLT entries. This results in
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// the userboot binary having simple PC-relative calls to addresses outside
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// its own image, to where the vDSO will be found at runtime.
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#define FUNCTION(name, address, size) \
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PROVIDE_HIDDEN(name = CODE_END + address);
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PROVIDE_HIDDEN(name = ALIGN(_end, CONSTANT(MAXPAGESIZE)) + address);
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#define WEAK_FUNCTION(name, address, size) FUNCTION(name, address, size)
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