Golang symbols in ELF files are different from C/C++
which contains special characters like '*', '(' and ')'.
With generics, things get more complicated, there are
symbols like:
github.com/cilium/ebpf/internal.(*Deque[go.shape.interface { Format(fmt.State, int32); TypeName() string;github.com/cilium/ebpf/btf.copy() github.com/cilium/ebpf/btf.Type}]).Grow
Matching such symbols using `%m[^\n]` in sscanf, this
excludes newline which typically does not appear in ELF
symbols. This should work in most use-cases and also
work for unicode letters in identifiers. If newline do
show up in ELF symbols, users can still attach to such
symbol by specifying bpf_uprobe_opts::func_name.
A working example can be found at this repo ([0]).
[0]: https://github.com/chenhengqi/libbpf-go-symbols
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230929155954.92448-1-hengqi.chen@gmail.com
Jiri Olsa says:
====================
hi,
at the moment we can't retrieve the number of missed kprobe
executions and subsequent execution of BPF programs.
This patchset adds:
- counting of missed execution on attach layer for:
. kprobes attached through perf link (kprobe/ftrace)
. kprobes attached through kprobe.multi link (fprobe)
- counting of recursion_misses for BPF kprobe programs
It's still technically possible to create kprobe without perf link (using
SET_BPF perf ioctl) in which case we don't have a way to retrieve the kprobe's
'missed' count. However both libbpf and cilium/ebpf libraries use perf link
if it's available, and for old kernels without perf link support we can use
BPF program to retrieve the kprobe missed count.
v3 changes:
- added acks [Song]
- make test_missed not serial [Andrii]
Also available at:
https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
bpf/missed_stats
thanks,
jirka
====================
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Adding selftest that puts kprobe on bpf_fentry_test1 that calls bpf_printk
and invokes bpf_trace_printk tracepoint. The bpf_trace_printk tracepoint
has test[234] programs attached to it.
Because kprobe execution goes through bpf_prog_active check, programs
attached to the tracepoint will fail the recursion check and increment the
recursion_misses stats.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Song Liu <song@kernel.org>
Reviewed-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/bpf/20230920213145.1941596-10-jolsa@kernel.org
Adding selftest that puts kprobe.multi on bpf_fentry_test1 that
calls bpf_kfunc_common_test kfunc which has 3 perf event kprobes
and 1 kprobe.multi attached.
Because fprobe (kprobe.multi attach layear) does not have strict
recursion check the kprobe's bpf_prog_active check is hit for test2-5.
Disabling this test for arm64, because there's no fprobe support yet.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Song Liu <song@kernel.org>
Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20230920213145.1941596-9-jolsa@kernel.org
Add missed value to kprobe attached through perf link info to
hold the stats of missed kprobe handler execution.
The kprobe's missed counter gets incremented when kprobe handler
is not executed due to another kprobe running on the same cpu.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230920213145.1941596-4-jolsa@kernel.org
Martin Kelly says:
====================
This patch series adds a new ring__ API to libbpf exposing getters for
accessing the individual ringbuffers inside a struct ring_buffer. This is
useful for polling individually, getting available data, or similar use
cases. The API looks like this, and was roughly proposed by Andrii Nakryiko
in another thread:
Getting a ring struct:
struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx);
Using the ring struct:
unsigned long ring__consumer_pos(const struct ring *r);
unsigned long ring__producer_pos(const struct ring *r);
size_t ring__avail_data_size(const struct ring *r);
size_t ring__size(const struct ring *r);
int ring__map_fd(const struct ring *r);
int ring__consume(struct ring *r);
Changes in v2:
- Addressed all feedback from Andrii Nakryiko
====================
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Switch rb->rings to be an array of pointers instead of a contiguous
block. This allows for each ring pointer to be stable after
ring_buffer__add is called, which allows us to expose struct ring * to
the user without gotchas. Without this change, the realloc in
ring_buffer__add could invalidate a struct ring *, making it unsafe to
give to the user.
Signed-off-by: Martin Kelly <martin.kelly@crowdstrike.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230925215045.2375758-3-martin.kelly@crowdstrike.com
Hengqi Chen says:
====================
Dynamic symbols in shared library may have the same name, for example:
$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
$ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
706: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 __pthread_rwlock_wrlock@GLIBC_2.2.5
2568: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@@GLIBC_2.34
2571: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@GLIBC_2.2.5
There are two pthread_rwlock_wrlock symbols in libc.so .dynsym section.
The one with @@ is the default version, the other is hidden.
Note that the version info is stored in .gnu.version and .gnu.version_d
sections of libc and the two symbols are at the _same_ offset.
Currently, specify `pthread_rwlock_wrlock`, `pthread_rwlock_wrlock@@GLIBC_2.34`
or `pthread_rwlock_wrlock@GLIBC_2.2.5` in bpf_uprobe_opts::func_name won't work.
Because there are two `pthread_rwlock_wrlock` in .dynsym sections without the
version suffix and both are global bind.
We could solve this by introducing symbol versioning ([0]). So that users can
specify func, func@LIB_VERSION or func@@LIB_VERSION to attach a uprobe.
This patchset resolves symbol conflicts and add symbol versioning for uprobe.
- Patch 1 resolves symbol conflicts at the same offset
- Patch 2 adds symbol versioning for dynsym
- Patch 3 adds selftests for the above changes
Changes from v3:
- Address comments from Andrii
Changes from v2:
- Add uretprobe selfttest (Alan)
- Check symbol exact match (Alan)
- Fix typo (Jiri)
Changes from v1:
- Address comments from Alan and Jiri
- Add selftests (Someone reminds me that there is an attempt at [1]
and part of the selftest code from Andrii is taken from there)
[0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html
[1]: https://lore.kernel.org/lkml/CAEf4BzZTrjjyyOm3ak9JsssPSh6T_ZmGd677a2rt5e5rBLUrpQ@mail.gmail.com/
====================
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
This exercises the newly added dynsym symbol versioning logics.
Now we accept symbols in form of func, func@LIB_VERSION or
func@@LIB_VERSION.
The test rely on liburandom_read.so. For liburandom_read.so, we have:
$ nm -D liburandom_read.so
w __cxa_finalize@GLIBC_2.17
w __gmon_start__
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
0000000000000000 A LIBURANDOM_READ_1.0.0
0000000000000000 A LIBURANDOM_READ_2.0.0
000000000000081c T urandlib_api@@LIBURANDOM_READ_2.0.0
0000000000000814 T urandlib_api@LIBURANDOM_READ_1.0.0
0000000000000824 T urandlib_api_sameoffset@LIBURANDOM_READ_1.0.0
0000000000000824 T urandlib_api_sameoffset@@LIBURANDOM_READ_2.0.0
000000000000082c T urandlib_read_without_sema@@LIBURANDOM_READ_1.0.0
00000000000007c4 T urandlib_read_with_sema@@LIBURANDOM_READ_1.0.0
0000000000011018 D urandlib_read_with_sema_semaphore@@LIBURANDOM_READ_1.0.0
For `urandlib_api`, specifying `urandlib_api` will cause a conflict because
there are two symbols named urandlib_api and both are global bind.
For `urandlib_api_sameoffset`, there are also two symbols in the .so, but
both are at the same offset and essentially they refer to the same function
so no conflict.
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230918024813.237475-4-hengqi.chen@gmail.com
In current implementation, we assume that symbol found in .dynsym section
would have a version suffix and use it to compare with symbol user supplied.
According to the spec ([0]), this assumption is incorrect, the version info
of dynamic symbols are stored in .gnu.version and .gnu.version_d sections
of ELF objects. For example:
$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
$ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
706: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 __pthread_rwlock_wrlock@GLIBC_2.2.5
2568: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@@GLIBC_2.34
2571: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@GLIBC_2.2.5
In this case, specify pthread_rwlock_wrlock@@GLIBC_2.34 or
pthread_rwlock_wrlock@GLIBC_2.2.5 in bpf_uprobe_opts::func_name won't work.
Because the qualified name does NOT match `pthread_rwlock_wrlock` (without
version suffix) in .dynsym sections.
This commit implements the symbol versioning for dynsym and allows user to
specify symbol in the following forms:
- func
- func@LIB_VERSION
- func@@LIB_VERSION
In case of symbol conflicts, error out and users should resolve it by
specifying a qualified name.
[0]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/symversion.html
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230918024813.237475-3-hengqi.chen@gmail.com
Dynamic symbols in shared library may have the same name, for example:
$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
000000000009b1a0 T __pthread_rwlock_wrlock@GLIBC_2.2.5
000000000009b1a0 T pthread_rwlock_wrlock@@GLIBC_2.34
000000000009b1a0 T pthread_rwlock_wrlock@GLIBC_2.2.5
$ readelf -W --dyn-syms /lib/x86_64-linux-gnu/libc.so.6 | grep rwlock_wrlock
706: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 __pthread_rwlock_wrlock@GLIBC_2.2.5
2568: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@@GLIBC_2.34
2571: 000000000009b1a0 878 FUNC GLOBAL DEFAULT 15 pthread_rwlock_wrlock@GLIBC_2.2.5
Currently, users can't attach a uprobe to pthread_rwlock_wrlock because
there are two symbols named pthread_rwlock_wrlock and both are global
bind. And libbpf considers it as a conflict.
Since both of them are at the same offset we could accept one of them
harmlessly. Note that we already does this in elf_resolve_syms_offsets.
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230918024813.237475-2-hengqi.chen@gmail.com
Commit 06744f2469 ("samples/bpf: Add openat2() enter/exit tracepoint
to syscall_tp sample") added two more eBPF programs to support the
openat2() syscall. However, it did not increase the size of the array
that holds the corresponding bpf_links. This leads to an out-of-bound
access on that array in the bpf_object__for_each_program loop and could
corrupt other variables on the stack. On our testing QEMU, it corrupts
the map1_fds array and causes the sample to fail:
# ./syscall_tp
prog #0: map ids 4 5
verify map:4 val: 5
map_lookup failed: Bad file descriptor
Dynamically allocate the array based on the number of programs reported
by libbpf to prevent similar inconsistencies in the future
Fixes: 06744f2469 ("samples/bpf: Add openat2() enter/exit tracepoint to syscall_tp sample")
Signed-off-by: Jinghao Jia <jinghao@linux.ibm.com>
Signed-off-by: Ruowen Qin <ruowenq2@illinois.edu>
Signed-off-by: Jinghao Jia <jinghao7@illinois.edu>
Link: https://lore.kernel.org/r/20230917214220.637721-4-jinghao7@illinois.edu
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Ilya Leoshkevich says:
====================
Implement cpuv4 support for s390x
v1: https://lore.kernel.org/bpf/20230830011128.1415752-1-iii@linux.ibm.com/
v1 -> v2:
- Redo Disable zero-extension for BPF_MEMSX as Puranjay and Alexei
suggested.
- Drop the bpf_ct_insert_entry() patch, it went in via the bpf tree.
- Rebase, don't apply A-bs because there were fixed conflicts.
Hi,
This series adds the cpuv4 support to the s390x eBPF JIT.
Patches 1-3 are preliminary bugfixes.
Patches 4-8 implement the new instructions.
Patches 9-10 enable the tests.
Best regards,
Ilya
====================
Link: https://lore.kernel.org/r/20230919101336.2223655-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Implement the cpuv4 load with sign-extension, which is encoded as
BPF_MEMSX (and, for internal uses cases only, BPF_PROBE_MEMSX).
This is the same as BPF_MEM and BPF_PROBE_MEM, but with sign
extension instead of zero extension, and s390x has the necessary
instructions: lgb, lgh and lgf.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230919101336.2223655-6-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Implement the cpuv4 register-to-register move with sign extension. It
is distinguished from the normal moves by non-zero values in
insn->off, which determine the source size. s390x has instructions to
deal with all of them: lbr, lhr, lgbr, lghr and lgfr.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230919101336.2223655-5-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
test_progs -t bind_perm,bpf_obj_pinning/mounted-str-rel fails when
the selftests directory is mounted under /mnt, which is a reasonable
thing to do when sharing the selftests residing on the host with a
virtual machine, e.g., using 9p.
The reason is that cgroup2 is mounted at /mnt and not unmounted,
causing subsequent tests that need to access the selftests directory
to fail.
Fix by unmounting it. The kernel maintains a mount stack, so this
reveals what was mounted there before. Introduce cgroup_workdir_mounted
in order to maintain idempotency. Make it thread-local in order to
support test_progs -j.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230919101336.2223655-3-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
On the architectures that use bpf_jit_needs_zext(), e.g., s390x, the
verifier incorrectly inserts a zero-extension after BPF_MEMSX, leading
to miscompilations like the one below:
24: 89 1a ff fe 00 00 00 00 "r1 = *(s16 *)(r10 - 2);" # zext_dst set
0x3ff7fdb910e: lgh %r2,-2(%r13,%r0) # load halfword
0x3ff7fdb9114: llgfr %r2,%r2 # wrong!
25: 65 10 00 03 00 00 7f ff if r1 s> 32767 goto +3 <l0_1> # check_cond_jmp_op()
Disable such zero-extensions. The JITs need to insert sign-extension
themselves, if necessary.
Suggested-by: Puranjay Mohan <puranjay12@gmail.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Puranjay Mohan <puranjay12@gmail.com>
Link: https://lore.kernel.org/r/20230919101336.2223655-2-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Pull networking fixes from Paolo Abeni:
"Including fixes from netfilter and bpf.
Current release - regressions:
- bpf: adjust size_index according to the value of KMALLOC_MIN_SIZE
- netfilter: fix entries val in rule reset audit log
- eth: stmmac: fix incorrect rxq|txq_stats reference
Previous releases - regressions:
- ipv4: fix null-deref in ipv4_link_failure
- netfilter:
- fix several GC related issues
- fix race between IPSET_CMD_CREATE and IPSET_CMD_SWAP
- eth: team: fix null-ptr-deref when team device type is changed
- eth: i40e: fix VF VLAN offloading when port VLAN is configured
- eth: ionic: fix 16bit math issue when PAGE_SIZE >= 64KB
Previous releases - always broken:
- core: fix ETH_P_1588 flow dissector
- mptcp: fix several connection hang-up conditions
- bpf:
- avoid deadlock when using queue and stack maps from NMI
- add override check to kprobe multi link attach
- hsr: properly parse HSRv1 supervisor frames.
- eth: igc: fix infinite initialization loop with early XDP redirect
- eth: octeon_ep: fix tx dma unmap len values in SG
- eth: hns3: fix GRE checksum offload issue"
* tag 'net-6.6-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (87 commits)
sfc: handle error pointers returned by rhashtable_lookup_get_insert_fast()
igc: Expose tx-usecs coalesce setting to user
octeontx2-pf: Do xdp_do_flush() after redirects.
bnxt_en: Flush XDP for bnxt_poll_nitroa0()'s NAPI
net: ena: Flush XDP packets on error.
net/handshake: Fix memory leak in __sock_create() and sock_alloc_file()
net: hinic: Fix warning-hinic_set_vlan_fliter() warn: variable dereferenced before check 'hwdev'
netfilter: ipset: Fix race between IPSET_CMD_CREATE and IPSET_CMD_SWAP
netfilter: nf_tables: fix memleak when more than 255 elements expired
netfilter: nf_tables: disable toggling dormant table state more than once
vxlan: Add missing entries to vxlan_get_size()
net: rds: Fix possible NULL-pointer dereference
team: fix null-ptr-deref when team device type is changed
net: bridge: use DEV_STATS_INC()
net: hns3: add 5ms delay before clear firmware reset irq source
net: hns3: fix fail to delete tc flower rules during reset issue
net: hns3: only enable unicast promisc when mac table full
net: hns3: fix GRE checksum offload issue
net: hns3: add cmdq check for vf periodic service task
net: stmmac: fix incorrect rxq|txq_stats reference
...
Pull finegrained timestamp reverts from Christian Brauner:
"Earlier this week we sent a few minor fixes for the multi-grained
timestamp work in [1]. While we were polishing those up after Linus
realized that there might be a nicer way to fix them we received a
regression report in [2] that fine grained timestamps break gnulib
tests and thus possibly other tools.
The kernel will elide fine-grain timestamp updates when no one is
actively querying for them to avoid performance impacts. So a sequence
like write(f1) stat(f2) write(f2) stat(f2) write(f1) stat(f1) may
result in timestamp f1 to be older than the final f2 timestamp even
though f1 was last written too but the second write didn't update the
timestamp.
Such plotholes can lead to subtle bugs when programs compare
timestamps. For example, the nap() function in [2] will estimate that
it needs to wait one ns on a fine-grain timestamp enabled filesytem
between subsequent calls to observe a timestamp change. But in general
we don't update timestamps with more than one jiffie if we think that
no one is actively querying for fine-grain timestamps to avoid
performance impacts.
While discussing various fixes the decision was to go back to the
drawing board and ultimately to explore a solution that involves only
exposing such fine-grained timestamps to nfs internally and never to
userspace.
As there are multiple solutions discussed the honest thing to do here
is not to fix this up or disable it but to cleanly revert. The general
infrastructure will probably come back but there is no reason to keep
this code in mainline.
The general changes to timestamp handling are valid and a good cleanup
that will stay. The revert is fully bisectable"
Link: https://lore.kernel.org/all/20230918-hirte-neuzugang-4c2324e7bae3@brauner [1]
Link: https://lore.kernel.org/all/bf0524debb976627693e12ad23690094e4514303.camel@linuxfromscratch.org [2]
* tag 'v6.6-rc3.vfs.ctime.revert' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
Revert "fs: add infrastructure for multigrain timestamps"
Revert "btrfs: convert to multigrain timestamps"
Revert "ext4: switch to multigrain timestamps"
Revert "xfs: switch to multigrain timestamps"
Revert "tmpfs: add support for multigrain timestamps"
Pull powerpc fixes from Michael Ellerman:
- A fix for breakpoint handling which was using get_user() while atomic
- Fix the Power10 HASHCHK handler which was using get_user() while
atomic
- A few build fixes for issues caused by recent changes
Thanks to Benjamin Gray, Christophe Leroy, Kajol Jain, and Naveen N Rao.
* tag 'powerpc-6.6-2' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
powerpc/dexcr: Move HASHCHK trap handler
powerpc/82xx: Select FSL_SOC
powerpc: Fix build issue with LD_DEAD_CODE_DATA_ELIMINATION and FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
powerpc/watchpoints: Annotate atomic context in more places
powerpc/watchpoint: Disable pagefaults when getting user instruction
powerpc/watchpoints: Disable preemption in thread_change_pc()
powerpc/perf/hv-24x7: Update domain value check
Pull xen fixes from Juergen Gross:
- remove some unused functions in the Xen event channel handling
- fix a regression (introduced during the merge window) when booting as
Xen PV guest
- small cleanup removing another strncpy() instance
* tag 'for-linus-6.6a-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
xen/efi: refactor deprecated strncpy
x86/xen: allow nesting of same lazy mode
x86/xen: move paravirt lazy code
arm/xen: remove lazy mode related definitions
xen: simplify evtchn_do_upcall() call maze
