Hi Dave,
On 27/09/2023 08:45, Dave Young wrote:
On Sun, 24 Sept 2023 at 00:47, Julien Olivain <[email protected]> wrote:
Commit 714fa115 "kexec/arm64: Simplify the code for zImage" introduced
a use of the memfd_create() system call, included in version
kexec-tools v2.0.27.
This system call was introduced in kernel commit [1], first included
in kernel v3.17 (released on 2014-10-05).
The memfd_create() glibc wrapper function was added much later in
commit [2], first included in glibc version 2.27 (released on
2018-02-01).
This direct use memfd_create() introduced a requirement on
Kernel >= 3.17 and glibc >= 2.27.
There is old toolchains like [3] for example (which ships gcc 7.3.1,
glibc 2.25 and includes kernel v4.10 headers), that can still be used
to build newer kernels. Even if such toolchains can be seen as
outdated, they are is still claimed as supported by recent kernel.
For example, Kernel v6.5.5 has a requirement on gcc version 5.1 and
greater. See [4].
Moreover, kexec-tools <= 2.0.26 could be compiled using recent
toolchains with alternative libc (e.g. uclibc-ng, musl) which are not
providing the memfd_create() wrapper.
When compiling kexec-tools v2.0.27 with a toolchain not providing the
memfd_create() syscall wrapper, the compilation fail with message:
kexec/kexec.c: In function 'copybuf_memfd':
kexec/kexec.c:645:7: warning: implicit declaration of function
'memfd_create'; did you mean 'SYS_memfd_create'?
[-Wimplicit-function-declaration]
fd = memfd_create("kernel", MFD_ALLOW_SEALING);
^~~~~~~~~~~~
SYS_memfd_create
kexec/kexec.c:645:30: error: 'MFD_ALLOW_SEALING' undeclared (first
use in this function); did you mean '_PC_ALLOC_SIZE_MIN'?
fd = memfd_create("kernel", MFD_ALLOW_SEALING);
^~~~~~~~~~~~~~~~~
_PC_ALLOC_SIZE_MIN
In order to let kexec-tools compile in a wider range of
configurations,
this commit adds a memfd_create() function check in autoconf configure
script, and adds a system call wrapper which will be used if the
function is not available. With this commit, the environment
requirement is relaxed to only kernel >= v3.17.
Note: this issue was found in kexec-tools integration in Buildroot [5]
using the command "utils/test-pkg -a -p kexec", which tests many
toolchain/arch combinations.
I guess maybe the test was done on non x86 arch, when I tried to
build on old versions
I got another failure of lacking "getrandom". Only quickly did a
build test with commenting out
the getrandom code, the build passed with your patch.
Thanks for testing!
Regarding the getrandom() issue: according to [1], it requires
Kernel 3.17 and glibc 2.25. It is also implemented in uclibc-ng
and musl which is why I didn't see the issue.
getrandom() being a GNU extension, it needs '_GNU_SOURCE' to be
defined in uclibc-ng. Patch [2] was proposed a while back to fix
builds on m68k and uclibc-ng.
Thanks
Dave
Best regards,
Julien.
[1] https://man7.org/linux/man-pages/man2/getrandom.2.html#HISTORY
[2]
https://lore.kernel.org/kexec/[email protected]/
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