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package/qemu: drop host kernel version check

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There is no clean way to check if a program will actually run using
host-qemu, making this check too restrictive.

Add a warning in the help text.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
This commit is contained in:
Adam Duskett 2019-06-23 17:23:41 -04:00 committed by Arnout Vandecappelle (Essensium/Mind)
parent 9c53c300d4
commit 64ef25d738
2 changed files with 6 additions and 22 deletions
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6
package/qemu/Config.in.host
View File

@ -64,6 +64,12 @@ config BR2_PACKAGE_HOST_QEMU_LINUX_USER_MODE
Enables the build of the user-land emulator, which allows to
run user-space applications.
Note that system calls made by the emulated user-land are
serviced by the running host kernel. Therefore, if the
kernel headers used by your target are more recent than
the running host kernel, you may run into invalid system
calls, which may yield surprising effects.
config BR2_PACKAGE_HOST_QEMU_VDE2
bool "VDE2 support"
help

22
package/qemu/qemu.mk
View File

@ -241,28 +241,6 @@ ifneq ($(HOST_QEMU_HOST_SYSTEM_TYPE),Linux)
$(error "qemu-user can only be used on Linux hosts")
endif
# kernel version as major*256 + minor
HOST_QEMU_HOST_SYSTEM_VERSION = $(shell uname -r | awk -F. '{ print $$1 * 256 + $$2 }')
HOST_QEMU_TARGET_SYSTEM_VERSION = $(shell echo $(BR2_TOOLCHAIN_HEADERS_AT_LEAST) | awk -F. '{ print $$1 * 256 + $$2 }')
HOST_QEMU_COMPARE_VERSION = $(shell test $(HOST_QEMU_HOST_SYSTEM_VERSION) -ge $(HOST_QEMU_TARGET_SYSTEM_VERSION) && echo OK)
#
# The principle of qemu-user is that it emulates the instructions of
# the target architecture when running the binary, and then when this
# binary does a system call, it converts this system call into a
# system call on the host machine. This mechanism makes an assumption:
# that the target binary will not do system calls that do not exist on
# the host. This basically requires that the target binary should be
# built with kernel headers that are older or the same as the kernel
# version running on the host machine.
#
ifeq ($(BR_BUILDING),y)
ifneq ($(HOST_QEMU_COMPARE_VERSION),OK)
$(error "Refusing to build qemu-user: target Linux version newer than host's.")
endif
endif # BR_BUILDING
else # BR2_PACKAGE_HOST_QEMU_LINUX_USER_MODE
HOST_QEMU_OPTS += --disable-linux-user
endif # BR2_PACKAGE_HOST_QEMU_LINUX_USER_MODE