kumquat-buildroot/package/glibc/glibc.mk
Yann E. MORIN 525ffc2bb1 package/glibc: allow runing on kernels older than used for the headers
Currently, we configure glibc to not add compatibility support for
kernels older than the one used for the headers. This is on the
expectation that the system will never run on a kernel that is older
than the one used for the headers or, when Buildroot builds the kernel,
on another, older kernel.

However, in some situations, it is possible to build for a generic
system, where the kernel may be a different version. This can be the
case, for example, when Building an image that is to be used in a
container that can run on a range of machines each with different kernel
versions. In such a case, it is interesting to build glibc in a way as
to take better advantage of the newer kernels, and thus using newer
kernel headers, while still allowing running on older kernels, and thus
carrying more compatibility code.

We add an option to glibc to allow the user to enable compatibility
shims. To simplify the case, when that option is enabled, we just let
glibc enable as old compatibility shims as supported by the current
architecture.

The code size increase is very small. For an ARM Cortex-A7, with
gcc-10.3.0, the delta is as follows (other files installed by glibc had
no size delta; sizes in bytes):
    file                  | no compat | compat    | delta
    ----------------------+-----------+-----------+-------
    ld-linux-armhf.so.3   | 200216    | 200284    | +  68
    libc.so.6             | 1814496   | 1823120   | +8624
                                            ------+-------
                                            Total | +8692

No runtime overhead has been measured; the overhead is most probably
in the measurement noise. Indeed, the compatibility shims are very
lightweight. For example, there are 9 arch-generic shims:
    renameat2(), execveat(), mlock2(), statx(), faccessat2(),
    close_range(), time64-related syscall shenanigans, a waitid()
    feature, and a futex operation (LOCK_PI2)
and then each arch may define a few others. i386 has less than 20
(mostly related to socket options, and one for the ordering of the
clone() arguments), while ARM seems to have only two (mlock2() and a
configurable futex feature).

Note: however, as Arnout pointed out, some programs may still actually
fail to run even with such compatibility shim, if they really expect the
shimed syscalls to really exist and have no fallback (and/or no proper
error-handling). Still, in the vast majority of cases, those
compatibility shims are enough to have a system running.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Cc: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Tested-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
2022-02-06 11:55:31 +01:00

175 lines
5.6 KiB
Makefile

################################################################################
#
# glibc
#
################################################################################
# Generate version string using:
# git describe --match 'glibc-*' --abbrev=40 origin/release/MAJOR.MINOR/master | cut -d '-' -f 2-
# When updating the version, please also update localedef
GLIBC_VERSION = 2.34-109-gd64b08d5ba7ffbc9155630f4843cf2e271b1629c
# Upstream doesn't officially provide an https download link.
# There is one (https://sourceware.org/git/glibc.git) but it's not reliable,
# sometimes the connection times out. So use an unofficial github mirror.
# When updating the version, check it on the official repository;
# *NEVER* decide on a version string by looking at the mirror.
# Then check that the mirror has been synced already (happens once a day.)
GLIBC_SITE = $(call github,bminor,glibc,$(GLIBC_VERSION))
GLIBC_LICENSE = GPL-2.0+ (programs), LGPL-2.1+, BSD-3-Clause, MIT (library)
GLIBC_LICENSE_FILES = COPYING COPYING.LIB LICENSES
GLIBC_CPE_ID_VENDOR = gnu
# glibc is part of the toolchain so disable the toolchain dependency
GLIBC_ADD_TOOLCHAIN_DEPENDENCY = NO
# Before glibc is configured, we must have the first stage
# cross-compiler and the kernel headers
GLIBC_DEPENDENCIES = host-gcc-initial linux-headers host-bison host-gawk \
$(BR2_MAKE_HOST_DEPENDENCY) $(BR2_PYTHON3_HOST_DEPENDENCY)
GLIBC_SUBDIR = build
GLIBC_INSTALL_STAGING = YES
GLIBC_INSTALL_STAGING_OPTS = install_root=$(STAGING_DIR) install
# Thumb build is broken, build in ARM mode
ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB),y)
GLIBC_EXTRA_CFLAGS += -marm
endif
# MIPS64 defaults to n32 so pass the correct -mabi if
# we are using a different ABI. OABI32 is also used
# in MIPS so we pass -mabi=32 in this case as well
# even though it's not strictly necessary.
ifeq ($(BR2_MIPS_NABI64),y)
GLIBC_EXTRA_CFLAGS += -mabi=64
else ifeq ($(BR2_MIPS_OABI32),y)
GLIBC_EXTRA_CFLAGS += -mabi=32
endif
ifeq ($(BR2_ENABLE_DEBUG),y)
GLIBC_EXTRA_CFLAGS += -g
endif
# glibc explicitly requires compile barriers between files
ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_7),y)
GLIBC_EXTRA_CFLAGS += -fno-lto
endif
# The stubs.h header is not installed by install-headers, but is
# needed for the gcc build. An empty stubs.h will work, as explained
# in http://gcc.gnu.org/ml/gcc/2002-01/msg00900.html. The same trick
# is used by Crosstool-NG.
ifeq ($(BR2_TOOLCHAIN_BUILDROOT_GLIBC),y)
define GLIBC_ADD_MISSING_STUB_H
mkdir -p $(STAGING_DIR)/usr/include/gnu
touch $(STAGING_DIR)/usr/include/gnu/stubs.h
endef
endif
GLIBC_CONF_ENV = \
ac_cv_path_BASH_SHELL=/bin/$(if $(BR2_PACKAGE_BASH),bash,sh) \
libc_cv_forced_unwind=yes \
libc_cv_ssp=no
# POSIX shell does not support localization, so remove the corresponding
# syntax from ldd if bash is not selected.
ifeq ($(BR2_PACKAGE_BASH),)
define GLIBC_LDD_NO_BASH
$(SED) 's/$$"/"/g' $(@D)/elf/ldd.bash.in
endef
GLIBC_POST_PATCH_HOOKS += GLIBC_LDD_NO_BASH
endif
# Override the default library locations of /lib64/<abi> and
# /usr/lib64/<abi>/ for RISC-V.
ifeq ($(BR2_riscv),y)
ifeq ($(BR2_RISCV_64),y)
GLIBC_CONF_ENV += libc_cv_slibdir=/lib64 libc_cv_rtlddir=/lib
else
GLIBC_CONF_ENV += libc_cv_slibdir=/lib32 libc_cv_rtlddir=/lib
endif
endif
# glibc requires make >= 4.0 since 2.28 release.
# https://www.sourceware.org/ml/libc-alpha/2018-08/msg00003.html
GLIBC_MAKE = $(BR2_MAKE)
GLIBC_CONF_ENV += ac_cv_prog_MAKE="$(BR2_MAKE)"
ifeq ($(BR2_PACKAGE_GLIBC_KERNEL_COMPAT),)
GLIBC_CONF_OPTS += --enable-kernel=$(call qstrip,$(BR2_TOOLCHAIN_HEADERS_AT_LEAST))
endif
# Even though we use the autotools-package infrastructure, we have to
# override the default configure commands for several reasons:
#
# 1. We have to build out-of-tree, but we can't use the same
# 'symbolic link to configure' used with the gcc packages.
#
# 2. We have to execute the configure script with bash and not sh.
#
# Note that as mentionned in
# http://patches.openembedded.org/patch/38849/, glibc must be
# built with -O2, so we pass our own CFLAGS and CXXFLAGS below.
define GLIBC_CONFIGURE_CMDS
mkdir -p $(@D)/build
# Do the configuration
(cd $(@D)/build; \
$(TARGET_CONFIGURE_OPTS) \
CFLAGS="-O2 $(GLIBC_EXTRA_CFLAGS)" CPPFLAGS="" \
CXXFLAGS="-O2 $(GLIBC_EXTRA_CFLAGS)" \
$(GLIBC_CONF_ENV) \
$(SHELL) $(@D)/configure \
--target=$(GNU_TARGET_NAME) \
--host=$(GNU_TARGET_NAME) \
--build=$(GNU_HOST_NAME) \
--prefix=/usr \
--enable-shared \
$(if $(BR2_x86_64),--enable-lock-elision) \
--with-pkgversion="Buildroot" \
--disable-profile \
--disable-werror \
--without-gd \
--with-headers=$(STAGING_DIR)/usr/include \
$(GLIBC_CONF_OPTS))
$(GLIBC_ADD_MISSING_STUB_H)
endef
#
# We also override the install to target commands since we only want
# to install the libraries, and nothing more.
#
GLIBC_LIBS_LIB = \
ld*.so.* libanl.so.* libc.so.* libcrypt.so.* libdl.so.* libgcc_s.so.* \
libm.so.* libpthread.so.* libresolv.so.* librt.so.* \
libutil.so.* libnss_files.so.* libnss_dns.so.* libmvec.so.*
ifeq ($(BR2_PACKAGE_GDB),y)
GLIBC_LIBS_LIB += libthread_db.so.*
endif
ifeq ($(BR2_PACKAGE_GLIBC_UTILS),y)
GLIBC_TARGET_UTILS_USR_BIN = posix/getconf elf/ldd
GLIBC_TARGET_UTILS_SBIN = elf/ldconfig
ifeq ($(BR2_SYSTEM_ENABLE_NLS),y)
GLIBC_TARGET_UTILS_USR_BIN += locale/locale
endif
endif
define GLIBC_INSTALL_TARGET_CMDS
for libpattern in $(GLIBC_LIBS_LIB); do \
$(call copy_toolchain_lib_root,$$libpattern) ; \
done
$(foreach util,$(GLIBC_TARGET_UTILS_USR_BIN), \
$(INSTALL) -D -m 0755 $(@D)/build/$(util) $(TARGET_DIR)/usr/bin/$(notdir $(util))
)
$(foreach util,$(GLIBC_TARGET_UTILS_SBIN), \
$(INSTALL) -D -m 0755 $(@D)/build/$(util) $(TARGET_DIR)/sbin/$(notdir $(util))
)
endef
$(eval $(autotools-package))