Split the query of HW-attached program from the software one.
Introduce new .ndo_bpf command to query HW-attached program.
This will allow drivers to install different programs in HW
and SW at the same time. Netlink can now also carry multiple
programs on dump (in which case mode will be set to
XDP_ATTACHED_MULTI and user has to check per-attachment point
attributes, IFLA_XDP_PROG_ID will not be present). We reuse
IFLA_XDP_PROG_ID skb space for second mode, so rtnl_xdp_size()
doesn't need to be updated.
Note that the installation side is still not there, since all
drivers currently reject installing more than one program at
the time.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Basic operations drivers perform during xdp setup and query can
be moved to helpers in the core. Encapsulate program and flags
into a structure and add helpers. Note that the structure is
intended as the "main" program information source in the driver.
Most drivers will additionally place the program pointer in their
fast path or ring structures.
The helpers don't have a huge impact now, but they will
decrease the code duplication when programs can be installed
in HW and driver at the same time. Encapsulating the basic
operations in helpers will hopefully also reduce the number
of changes to drivers which adopt them.
Helpers could really be static inline, but they depend on
definition of struct netdev_bpf which means they'd have
to be placed in netdevice.h, an already 4500 line header.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
prog_attached of struct netdev_bpf should have been superseded
by simply setting prog_id long time ago, but we kept it around
to allow offloading drivers to communicate attachment mode (drv
vs hw). Subsequently drivers were also allowed to report back
attachment flags (prog_flags), and since nowadays only programs
attached will XDP_FLAGS_HW_MODE can get offloaded, we can tell
the attachment mode from the flags driver reports. Remove
prog_attached member.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
In preparation for support of simultaneous driver and hardware XDP
support add per-mode attributes. The catch-all IFLA_XDP_PROG_ID
will still be reported, but user space can now also access the
program ID in a new IFLA_XDP_<mode>_PROG_ID attribute.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Russell King says:
====================
Four further jit compiler improves for 32-bit ARM.
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Improve the 64-bit store implementation from:
ldr r6, [fp, #-8]
str r8, [r6]
ldr r6, [fp, #-8]
mov r7, #4
add r7, r6, r7
str r9, [r7]
to:
ldr r6, [fp, #-8]
str r8, [r6]
str r9, [r6, #4]
We leave the store as two separate STR instructions rather than using
STRD as the store may not be aligned, and STR can handle misalignment.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Rather than writing each 32-bit half of the 64-bit immediate value
separately when the register is on the stack:
movw r6, #45056 ; 0xb000
movt r6, #60979 ; 0xee33
str r6, [fp, #-44] ; 0xffffffd4
mov r6, #0
str r6, [fp, #-40] ; 0xffffffd8
arrange to use the double-word store when available instead:
movw r6, #45056 ; 0xb000
movt r6, #60979 ; 0xee33
mov r7, #0
strd r6, [fp, #-44] ; 0xffffffd4
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Russell King says:
====================
This series improves the ARM BPF JIT compiler by:
- enumerating the stack layout rather than using constants that happen
to be multiples of four
- rejig the BPF "register" accesses to use negative numbers instead of
positive, which could be confused with register numbers in the bpf2a32
array.
- since we maintain the ARM FP register as a pointer to the top of our
scratch space (or, with frame pointers enabled, a valid ARM frame
pointer register), we can access our scratch space using FP, which is
constant across all BPF programs, including tail-called programs.
- use immediate forms of ARM instructions where possible, rather than
first loading the immediate into an ARM register.
- use load-with-shift instruction rather than seperate shift instruction
followed by load
- avoid reloading index and array in the tail-call code
- use double-word load/store instructions where available
Version 2:
- Fix ARMv5 test pointed out by Olof
- Fix build error found by 0-day (adding an additional patch)
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Use double-word load and stores where support for this instruction is
supported by the CPU architecture.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Always use an odd/even register pair for our 64-bit registers, so that
we're able to use the double-word load/store instructions in the future.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Rearranging the order of the initial tail call code a little allows is
to avoid reloading the 'array' pointer.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Avoid reloading 'index' after we have validated it - it remains in
tmp2[1] up to the point that we begin the code to index the pointer
array, so with a little rearrangement of the registers, we can use
the already loaded value.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Rather than pre-shifting the rm register for the ldr in the tail call,
shift it in the load instruction. This eliminates one unnecessary
instruction.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Rather than moving constants to a register and then using them in a
subsequent instruction, use them directly in the desired instruction
cutting out the "middle" register. This removes two instructions from
the tail call code path.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Provide a version of the imm8m() function that the compiler can optimise
when used with a constant expression.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Access the eBPF scratch space using the frame pointer rather than our
stack pointer, as the offsets from the ARM frame pointer are constant
across all eBPF programs.
Since we no longer reference the scratch space registers from the stack
pointer, this simplifies emit_push_r64() as it no longer needs to know
how many words are pushed onto the stack.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Provide a couple of 64-bit register accessors, and use them where
appropriate
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Many of the code paths need to have knowledge about whether a register
is stacked or in a CPU register. Move this decision making to a pair
of helper functions instead of having it scattered throughout the
code.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The decision about whether a BPF register is on the stack or in a CPU
register is detected at the top BPF insn processing level, and then
percolated throughout the remainder of the code. Since we now use
negative register values to represent stacked registers, we can detect
where a BPF register is stored without restoring to carrying this
additional metadata through all code paths.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Use negative numbers for eBPF registers that live on the stack.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Provide a set of load/store opcode generators that work with negative
immediates as well as positive ones.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Enumerate the contents of the JIT scratch stack layout used for storing
some of the JITs 64-bit registers, tail call counter and AX register.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Quentin Monnet says:
====================
The three patches in this series are related to the documentation for eBPF
helpers. The first patch brings minor formatting edits to the documentation
in include/uapi/linux/bpf.h, and the second one updates the related header
file under tools/.
The third patch adds a Makefile under tools/bpf for generating the
documentation (man pages) about eBPF helpers. The targets defined in this
file can also be called from the bpftool directory (please refer to
relevant commit logs for details).
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Provide a new Makefile.helpers in tools/bpf, in order to build and
install the man page for eBPF helpers. This Makefile is also included in
the one used to build bpftool documentation, so that it can be called
either on its own (cd tools/bpf && make -f Makefile.helpers) or from
bpftool directory (cd tools/bpf/bpftool && make doc, or
cd tools/bpf/bpftool/Documentation && make helpers).
Makefile.helpers is not added directly to bpftool to avoid changing its
Makefile too much (helpers are not 100% directly related with bpftool).
But the possibility to build the page from bpftool directory makes us
able to package the helpers man page with bpftool, and to install it
along with bpftool documentation, so that the doc for helpers becomes
easily available to developers through the "man" program.
Cc: linux-man@vger.kernel.org
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Update with latest changes from include/uapi/linux/bpf.h header.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Minor formatting edits for eBPF helpers documentation, including blank
lines removal, fix of item list for return values in bpf_fib_lookup(),
and missing prefix on bpf_skb_load_bytes_relative().
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Jakub Kicinski says:
====================
This series starts with two minor clean ups to test_offload.py
selftest script.
The next 11 patches extend the abilities of bpftool prog load
beyond the simple cgroup use cases. Three new parameters are
added:
- type - allows specifying program type, independent of how
code sections are named;
- map - allows reusing existing maps, instead of creating a new
map on every program load;
- dev - offload/binding to a device.
A number of changes to libbpf is required to accomplish the task.
The section - program type logic mapping is exposed. We should
probably aim to use the libbpf program section naming everywhere.
For reuse of maps we need to allow users to set FD for bpf map
object in libbpf.
Examples
Load program my_xdp.o and pin it as /sys/fs/bpf/my_xdp, for xdp
program type:
$ bpftool prog load my_xdp.o /sys/fs/bpf/my_xdp \
type xdp
As above but for offload:
$ bpftool prog load my_xdp.o /sys/fs/bpf/my_xdp \
type xdp \
dev netdevsim0
Load program my_maps.o, but for the first map reuse map id 17,
and for the map called "other_map" reuse pinned map /sys/fs/bpf/map0:
$ bpftool prog load my_maps.o /sys/fs/bpf/prog \
map idx 0 id 17 \
map name other_map pinned /sys/fs/bpf/map0
v3:
- fix return codes in patch 5;
- rename libbpf_prog_type_by_string() -> libbpf_prog_type_by_name();
- fold file path into xattr in patch 8;
- add patch 10;
- use dup3() in patch 12;
- depend on fd value in patch 12;
- close old fd in patch 12.
v2:
- add compat for reallocarray().
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Add map parameter to prog load which will allow reuse of existing
maps instead of creating new ones.
We need feature detection and compat code for reallocarray, since
it's not available in many libc versions.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
More advanced applications may want to only replace programs without
destroying associated maps. Allow libbpf users to achieve that.
Instead of always creating all of the maps at load time, expose to
users an API to reconstruct the map object from already existing
map.
The map parameters are read from the kernel and replace the parameters
of the ELF map. libbpf does not restrict the map replacement, i.e.
the reused map does not have to be compatible with the ELF map
definition. We relay on the verifier for checking the compatibility
between maps and programs. The ELF map definition is completely
overwritten by the information read from the kernel, to make sure
libbpf's view of map object corresponds to the actual map.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
reallocarray() is a safer variant of realloc which checks for
multiplication overflow in case of array allocation. Since it's
not available in Glibc < 2.26 import kernel's overflow.h and
add a static inline implementation when needed. Use feature
detection to probe for existence of reallocarray.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
libbpf_strerror() depends on XSI-compliant (POSIX) version of
strerror_r(), which prevents us from using GNU-extensions in
libbpf.c, like reallocarray() or dup3(). Move error printing
code into a separate file to allow it to continue using POSIX
strerror_r().
No functional changes.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
bpf_prog_load() is a very useful helper but it doesn't give us full
flexibility of modifying the BPF objects before loading. Open code
bpf_prog_load() in bpftool so we can add extra logic in following
commits.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Similarly to bpf_prog_load() users of bpf_object__open() may need
to specify the expected program type. Program type is needed at
open to avoid the kernel version check for program types which don't
require it.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Add helper to libbpf for recognizing maps which should not have
ifindex set when program is loaded. These maps only contain
host metadata and therefore are not marked for offload, e.g.
the perf event map.
Use this helper in bpf_prog_load_xattr().
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Sometimes program section names don't match with libbpf's expectation.
In particular XDP's default section names differ between libbpf and
iproute2. Allow users to pass program type on command line. Name
the types like the libbpf expected section names.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
libbpf can guess program type based on ELF section names. As libbpf
becomes more popular its association between section name strings and
types becomes more of a standard. Allow libbpf users to use the same
logic for matching strings to types, e.g. when the string originates
from command line.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Extend the bpftool prog load command to also accept "dev"
parameter, which will allow us to load programs onto devices.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Add a new macro for printing more informative message than straight
usage() when parameters are missing, and use it for prog do_load().
Save the object and pin path argument to variables for clarity.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Currently the test only checks errors, not warnings, so save typing
and prefix the extack messages with "Error:" inside the check helper.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Trivial removal of duplicated "mode" in error message.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Jiong Wang says:
====================
NFP supports u16 and u32 multiplication. Multiplication is done 8-bits per
step, therefore we need 2 steps for u16 and 4 steps for u32.
We also need one start instruction to initialize the sequence and one or
two instructions to fetch the result depending on either you need the high
halve of u32 multiplication.
For ALU64, if either operand is beyond u32's value range, we reject it. One
thing to note, if the source operand is BPF_K, then we need to check "imm"
field directly, and we'd reject it if it is negative. Because for ALU64,
"imm" (with s32 type) is expected to be sign extended to s64 which NFP mul
doesn't support. For ALU32, it is fine for "imm" be negative though,
because the result is 32-bits and here is no difference on the low halve
of result for signed/unsigned mul, so we will get correct result.
NFP doesn't have integer divide instruction, this patch set uses reciprocal
algorithm (the basic one, reciprocal_div) to emulate it.
For each u32 divide, we would need 11 instructions to finish the operation.
7 (for multiplication) + 4 (various ALUs) = 11
Given NFP only supports multiplication no bigger than u32, we'd require
divisor and dividend no bigger than that as well.
Also eBPF doesn't support signed divide and has enforced this on C language
level by failing compilation. However LLVM assembler hasn't enforced this,
so it is possible for negative constant to leak in as a BPF_K operand
through assembly code, we reject such cases as well.
Meanwhile reciprocal_div.h only implemented the basic version of:
"Division by Invariant Integers Using Multiplication"
- Torbjörn Granlund and Peter L. Montgomery
This patch set further implements the optimized version (Figure 4.2 in the
paper) inside existing reciprocal_div.h. When the divider is even and the
calculated reciprocal magic number doesn't fit u32, we could reduce the
required ALU instructions from 4 to 2 or 1 for some cases.
The advanced version requires more complex calculation to get the
reciprocal multiplier and other control variables, but then could reduce
the required emulation operations. It makes sense to use it for JIT divide
code generation (for example eBPF JIT backends) for which we are willing to
trade performance of JITed code with that of host.
v2:
- add warning in l == 32 code path. (Song Liu/Jakub)
- jit separate insn sequence for l == 32. (Jakub/Edwin)
- should use unrestricted operand for mul.
- once place should use "1U << exp" instead of "1 << exp".
====================
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
As we are doing JIT, we would want to use the advanced version of the
reciprocal divide (reciprocal_value_adv) to trade performance with host.
We could reduce the required ALU instructions from 4 to 2 or 1.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
NFP doesn't have integer divide instruction, this patch use reciprocal
algorithm (the basic one, reciprocal_div) to emulate it.
For each u32 divide, we would need 11 instructions to finish the operation.
7 (for multiplication) + 4 (various ALUs) = 11
Given NFP only supports multiplication no bigger than u32, we'd require
divisor and dividend no bigger than that as well.
Also eBPF doesn't support signed divide and has enforced this on C language
level by failing compilation. However LLVM assembler hasn't enforced this,
so it is possible for negative constant to leak in as a BPF_K operand
through assembly code, we reject such cases as well.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
NFP supports u16 and u32 multiplication. Multiplication is done 8-bits per
step, therefore we need 2 steps for u16 and 4 steps for u32.
We also need one start instruction to initialize the sequence and one or
two instructions to fetch the result depending on either you need the high
halve of u32 multiplication.
For ALU64, if either operand is beyond u32's value range, we reject it. One
thing to note, if the source operand is BPF_K, then we need to check "imm"
field directly, and we'd reject it if it is negative. Because for ALU64,
"imm" (with s32 type) is expected to be sign extended to s64 which NFP mul
doesn't support. For ALU32, it is fine for "imm" be negative though,
because the result is 32-bits and here is no difference on the low halve
of result for signed/unsigned mul, so we will get correct result.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
NFP verifier hook is coping range information of the shift amount for
indirect shift operation so optimized shift sequences could be generated.
We want to use range info to do more things. For example, to decide whether
multiplication and divide are supported on the given range.
This patch simply let NFP verifier hook to copy range info for all operands
of all ALU operands.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The two fields are a copy of umin and umax info of bpf_insn->src_reg
generated by verifier.
Rename to make their meaning clear.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
The new added "reciprocal_value_adv" implements the advanced version of the
algorithm described in Figure 4.2 of the paper except when
"divisor > (1U << 31)" whose ceil(log2(d)) result will be 32 which then
requires u128 divide on host. The exception case could be easily handled
before calling "reciprocal_value_adv".
The advanced version requires more complex calculation to get the
reciprocal multiplier and other control variables, but then could reduce
the required emulation operations.
It makes no sense to use this advanced version for host divide emulation,
those extra complexities for calculating multiplier etc could completely
waive our saving on emulation operations.
However, it makes sense to use it for JIT divide code generation (for
example eBPF JIT backends) for which we are willing to trade performance of
JITed code with that of host. As shown by the following pseudo code, the
required emulation operations could go down from 6 (the basic version) to 3
or 4.
To use the result of "reciprocal_value_adv", suppose we want to calculate
n/d, the C-style pseudo code will be the following, it could be easily
changed to real code generation for other JIT targets.
struct reciprocal_value_adv rvalue;
u8 pre_shift, exp;
// handle exception case.
if (d >= (1U << 31)) {
result = n >= d;
return;
}
rvalue = reciprocal_value_adv(d, 32)
exp = rvalue.exp;
if (rvalue.is_wide_m && !(d & 1)) {
// floor(log2(d & (2^32 -d)))
pre_shift = fls(d & -d) - 1;
rvalue = reciprocal_value_adv(d >> pre_shift, 32 - pre_shift);
} else {
pre_shift = 0;
}
// code generation starts.
if (imm == 1U << exp) {
result = n >> exp;
} else if (rvalue.is_wide_m) {
// pre_shift must be zero when reached here.
t = (n * rvalue.m) >> 32;
result = n - t;
result >>= 1;
result += t;
result >>= rvalue.sh - 1;
} else {
if (pre_shift)
result = n >> pre_shift;
result = ((u64)result * rvalue.m) >> 32;
result >>= rvalue.sh;
}
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit adds a bash completion to the bpftool cgroup tree
command.
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Quentin Monnet <quentin.monnet@netronome.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
