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author | 2023-02-21 18:24:12 -0800 | |
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committer | 2023-02-21 18:24:12 -0800 | |
commit | 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch) | |
tree | cc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/bpf/llvm_reloc.rst | |
download | linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip |
Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted
Pull networking updates from Jakub Kicinski:
"Core:
- Add dedicated kmem_cache for typical/small skb->head, avoid having
to access struct page at kfree time, and improve memory use.
- Introduce sysctl to set default RPS configuration for new netdevs.
- Define Netlink protocol specification format which can be used to
describe messages used by each family and auto-generate parsers.
Add tools for generating kernel data structures and uAPI headers.
- Expose all net/core sysctls inside netns.
- Remove 4s sleep in netpoll if carrier is instantly detected on
boot.
- Add configurable limit of MDB entries per port, and port-vlan.
- Continue populating drop reasons throughout the stack.
- Retire a handful of legacy Qdiscs and classifiers.
Protocols:
- Support IPv4 big TCP (TSO frames larger than 64kB).
- Add IP_LOCAL_PORT_RANGE socket option, to control local port range
on socket by socket basis.
- Track and report in procfs number of MPTCP sockets used.
- Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
manager.
- IPv6: don't check net.ipv6.route.max_size and rely on garbage
collection to free memory (similarly to IPv4).
- Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).
- ICMP: add per-rate limit counters.
- Add support for user scanning requests in ieee802154.
- Remove static WEP support.
- Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
reporting.
- WiFi 7 EHT channel puncturing support (client & AP).
BPF:
- Add a rbtree data structure following the "next-gen data structure"
precedent set by recently added linked list, that is, by using
kfunc + kptr instead of adding a new BPF map type.
- Expose XDP hints via kfuncs with initial support for RX hash and
timestamp metadata.
- Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
better support decap on GRE tunnel devices not operating in collect
metadata.
- Improve x86 JIT's codegen for PROBE_MEM runtime error checks.
- Remove the need for trace_printk_lock for bpf_trace_printk and
bpf_trace_vprintk helpers.
- Extend libbpf's bpf_tracing.h support for tracing arguments of
kprobes/uprobes and syscall as a special case.
- Significantly reduce the search time for module symbols by
livepatch and BPF.
- Enable cpumasks to be used as kptrs, which is useful for tracing
programs tracking which tasks end up running on which CPUs in
different time intervals.
- Add support for BPF trampoline on s390x and riscv64.
- Add capability to export the XDP features supported by the NIC.
- Add __bpf_kfunc tag for marking kernel functions as kfuncs.
- Add cgroup.memory=nobpf kernel parameter option to disable BPF
memory accounting for container environments.
Netfilter:
- Remove the CLUSTERIP target. It has been marked as obsolete for
years, and we still have WARN splats wrt races of the out-of-band
/proc interface installed by this target.
- Add 'destroy' commands to nf_tables. They are identical to the
existing 'delete' commands, but do not return an error if the
referenced object (set, chain, rule...) did not exist.
Driver API:
- Improve cpumask_local_spread() locality to help NICs set the right
IRQ affinity on AMD platforms.
- Separate C22 and C45 MDIO bus transactions more clearly.
- Introduce new DCB table to control DSCP rewrite on egress.
- Support configuration of Physical Layer Collision Avoidance (PLCA)
Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
shared medium Ethernet.
- Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
preemption of low priority frames by high priority frames.
- Add support for controlling MACSec offload using netlink SET.
- Rework devlink instance refcounts to allow registration and
de-registration under the instance lock. Split the code into
multiple files, drop some of the unnecessarily granular locks and
factor out common parts of netlink operation handling.
- Add TX frame aggregation parameters (for USB drivers).
- Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
messages with notifications for debug.
- Allow offloading of UDP NEW connections via act_ct.
- Add support for per action HW stats in TC.
- Support hardware miss to TC action (continue processing in SW from
a specific point in the action chain).
- Warn if old Wireless Extension user space interface is used with
modern cfg80211/mac80211 drivers. Do not support Wireless
Extensions for Wi-Fi 7 devices at all. Everyone should switch to
using nl80211 interface instead.
- Improve the CAN bit timing configuration. Use extack to return
error messages directly to user space, update the SJW handling,
including the definition of a new default value that will benefit
CAN-FD controllers, by increasing their oscillator tolerance.
New hardware / drivers:
- Ethernet:
- nVidia BlueField-3 support (control traffic driver)
- Ethernet support for imx93 SoCs
- Motorcomm yt8531 gigabit Ethernet PHY
- onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
- Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
- Amlogic gxl MDIO mux
- WiFi:
- RealTek RTL8188EU (rtl8xxxu)
- Qualcomm Wi-Fi 7 devices (ath12k)
- CAN:
- Renesas R-Car V4H
Drivers:
- Bluetooth:
- Set Per Platform Antenna Gain (PPAG) for Intel controllers.
- Ethernet NICs:
- Intel (1G, igc):
- support TSN / Qbv / packet scheduling features of i226 model
- Intel (100G, ice):
- use GNSS subsystem instead of TTY
- multi-buffer XDP support
- extend support for GPIO pins to E823 devices
- nVidia/Mellanox:
- update the shared buffer configuration on PFC commands
- implement PTP adjphase function for HW offset control
- TC support for Geneve and GRE with VF tunnel offload
- more efficient crypto key management method
- multi-port eswitch support
- Netronome/Corigine:
- add DCB IEEE support
- support IPsec offloading for NFP3800
- Freescale/NXP (enetc):
- support XDP_REDIRECT for XDP non-linear buffers
- improve reconfig, avoid link flap and waiting for idle
- support MAC Merge layer
- Other NICs:
- sfc/ef100: add basic devlink support for ef100
- ionic: rx_push mode operation (writing descriptors via MMIO)
- bnxt: use the auxiliary bus abstraction for RDMA
- r8169: disable ASPM and reset bus in case of tx timeout
- cpsw: support QSGMII mode for J721e CPSW9G
- cpts: support pulse-per-second output
- ngbe: add an mdio bus driver
- usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
- r8152: handle devices with FW with NCM support
- amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
- virtio-net: support multi buffer XDP
- virtio/vsock: replace virtio_vsock_pkt with sk_buff
- tsnep: XDP support
- Ethernet high-speed switches:
- nVidia/Mellanox (mlxsw):
- add support for latency TLV (in FW control messages)
- Microchip (sparx5):
- separate explicit and implicit traffic forwarding rules, make
the implicit rules always active
- add support for egress DSCP rewrite
- IS0 VCAP support (Ingress Classification)
- IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
etc.)
- ES2 VCAP support (Egress Access Control)
- support for Per-Stream Filtering and Policing (802.1Q,
8.6.5.1)
- Ethernet embedded switches:
- Marvell (mv88e6xxx):
- add MAB (port auth) offload support
- enable PTP receive for mv88e6390
- NXP (ocelot):
- support MAC Merge layer
- support for the the vsc7512 internal copper phys
- Microchip:
- lan9303: convert to PHYLINK
- lan966x: support TC flower filter statistics
- lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
- lan937x: support Credit Based Shaper configuration
- ksz9477: support Energy Efficient Ethernet
- other:
- qca8k: convert to regmap read/write API, use bulk operations
- rswitch: Improve TX timestamp accuracy
- Intel WiFi (iwlwifi):
- EHT (Wi-Fi 7) rate reporting
- STEP equalizer support: transfer some STEP (connection to radio
on platforms with integrated wifi) related parameters from the
BIOS to the firmware.
- Qualcomm 802.11ax WiFi (ath11k):
- IPQ5018 support
- Fine Timing Measurement (FTM) responder role support
- channel 177 support
- MediaTek WiFi (mt76):
- per-PHY LED support
- mt7996: EHT (Wi-Fi 7) support
- Wireless Ethernet Dispatch (WED) reset support
- switch to using page pool allocator
- RealTek WiFi (rtw89):
- support new version of Bluetooth co-existance
- Mobile:
- rmnet: support TX aggregation"
* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
page_pool: add a comment explaining the fragment counter usage
net: ethtool: fix __ethtool_dev_mm_supported() implementation
ethtool: pse-pd: Fix double word in comments
xsk: add linux/vmalloc.h to xsk.c
sefltests: netdevsim: wait for devlink instance after netns removal
selftest: fib_tests: Always cleanup before exit
net/mlx5e: Align IPsec ASO result memory to be as required by hardware
net/mlx5e: TC, Set CT miss to the specific ct action instance
net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
net/mlx5: Refactor tc miss handling to a single function
net/mlx5: Kconfig: Make tc offload depend on tc skb extension
net/sched: flower: Support hardware miss to tc action
net/sched: flower: Move filter handle initialization earlier
net/sched: cls_api: Support hardware miss to tc action
net/sched: Rename user cookie and act cookie
sfc: fix builds without CONFIG_RTC_LIB
sfc: clean up some inconsistent indentings
net/mlx4_en: Introduce flexible array to silence overflow warning
net: lan966x: Fix possible deadlock inside PTP
net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
...
Diffstat (limited to 'Documentation/bpf/llvm_reloc.rst')
-rw-r--r-- | Documentation/bpf/llvm_reloc.rst | 240 |
1 files changed, 240 insertions, 0 deletions
diff --git a/Documentation/bpf/llvm_reloc.rst b/Documentation/bpf/llvm_reloc.rst new file mode 100644 index 000000000..ca8957d5b --- /dev/null +++ b/Documentation/bpf/llvm_reloc.rst @@ -0,0 +1,240 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +==================== +BPF LLVM Relocations +==================== + +This document describes LLVM BPF backend relocation types. + +Relocation Record +================= + +LLVM BPF backend records each relocation with the following 16-byte +ELF structure:: + + typedef struct + { + Elf64_Addr r_offset; // Offset from the beginning of section. + Elf64_Xword r_info; // Relocation type and symbol index. + } Elf64_Rel; + +For example, for the following code:: + + int g1 __attribute__((section("sec"))); + int g2 __attribute__((section("sec"))); + static volatile int l1 __attribute__((section("sec"))); + static volatile int l2 __attribute__((section("sec"))); + int test() { + return g1 + g2 + l1 + l2; + } + +Compiled with ``clang -target bpf -O2 -c test.c``, the following is +the code with ``llvm-objdump -dr test.o``:: + + 0: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll + 0000000000000000: R_BPF_64_64 g1 + 2: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0) + 3: 18 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r2 = 0 ll + 0000000000000018: R_BPF_64_64 g2 + 5: 61 20 00 00 00 00 00 00 r0 = *(u32 *)(r2 + 0) + 6: 0f 10 00 00 00 00 00 00 r0 += r1 + 7: 18 01 00 00 08 00 00 00 00 00 00 00 00 00 00 00 r1 = 8 ll + 0000000000000038: R_BPF_64_64 sec + 9: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0) + 10: 0f 10 00 00 00 00 00 00 r0 += r1 + 11: 18 01 00 00 0c 00 00 00 00 00 00 00 00 00 00 00 r1 = 12 ll + 0000000000000058: R_BPF_64_64 sec + 13: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0) + 14: 0f 10 00 00 00 00 00 00 r0 += r1 + 15: 95 00 00 00 00 00 00 00 exit + +There are four relations in the above for four ``LD_imm64`` instructions. +The following ``llvm-readelf -r test.o`` shows the binary values of the four +relocations:: + + Relocation section '.rel.text' at offset 0x190 contains 4 entries: + Offset Info Type Symbol's Value Symbol's Name + 0000000000000000 0000000600000001 R_BPF_64_64 0000000000000000 g1 + 0000000000000018 0000000700000001 R_BPF_64_64 0000000000000004 g2 + 0000000000000038 0000000400000001 R_BPF_64_64 0000000000000000 sec + 0000000000000058 0000000400000001 R_BPF_64_64 0000000000000000 sec + +Each relocation is represented by ``Offset`` (8 bytes) and ``Info`` (8 bytes). +For example, the first relocation corresponds to the first instruction +(Offset 0x0) and the corresponding ``Info`` indicates the relocation type +of ``R_BPF_64_64`` (type 1) and the entry in the symbol table (entry 6). +The following is the symbol table with ``llvm-readelf -s test.o``:: + + Symbol table '.symtab' contains 8 entries: + Num: Value Size Type Bind Vis Ndx Name + 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND + 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS test.c + 2: 0000000000000008 4 OBJECT LOCAL DEFAULT 4 l1 + 3: 000000000000000c 4 OBJECT LOCAL DEFAULT 4 l2 + 4: 0000000000000000 0 SECTION LOCAL DEFAULT 4 sec + 5: 0000000000000000 128 FUNC GLOBAL DEFAULT 2 test + 6: 0000000000000000 4 OBJECT GLOBAL DEFAULT 4 g1 + 7: 0000000000000004 4 OBJECT GLOBAL DEFAULT 4 g2 + +The 6th entry is global variable ``g1`` with value 0. + +Similarly, the second relocation is at ``.text`` offset ``0x18``, instruction 3, +for global variable ``g2`` which has a symbol value 4, the offset +from the start of ``.data`` section. + +The third and fourth relocations refers to static variables ``l1`` +and ``l2``. From ``.rel.text`` section above, it is not clear +which symbols they really refers to as they both refers to +symbol table entry 4, symbol ``sec``, which has ``STT_SECTION`` type +and represents a section. So for static variable or function, +the section offset is written to the original insn +buffer, which is called ``A`` (addend). Looking at +above insn ``7`` and ``11``, they have section offset ``8`` and ``12``. +From symbol table, we can find that they correspond to entries ``2`` +and ``3`` for ``l1`` and ``l2``. + +In general, the ``A`` is 0 for global variables and functions, +and is the section offset or some computation result based on +section offset for static variables/functions. The non-section-offset +case refers to function calls. See below for more details. + +Different Relocation Types +========================== + +Six relocation types are supported. The following is an overview and +``S`` represents the value of the symbol in the symbol table:: + + Enum ELF Reloc Type Description BitSize Offset Calculation + 0 R_BPF_NONE None + 1 R_BPF_64_64 ld_imm64 insn 32 r_offset + 4 S + A + 2 R_BPF_64_ABS64 normal data 64 r_offset S + A + 3 R_BPF_64_ABS32 normal data 32 r_offset S + A + 4 R_BPF_64_NODYLD32 .BTF[.ext] data 32 r_offset S + A + 10 R_BPF_64_32 call insn 32 r_offset + 4 (S + A) / 8 - 1 + +For example, ``R_BPF_64_64`` relocation type is used for ``ld_imm64`` instruction. +The actual to-be-relocated data (0 or section offset) +is stored at ``r_offset + 4`` and the read/write +data bitsize is 32 (4 bytes). The relocation can be resolved with +the symbol value plus implicit addend. Note that the ``BitSize`` is 32 which +means the section offset must be less than or equal to ``UINT32_MAX`` and this +is enforced by LLVM BPF backend. + +In another case, ``R_BPF_64_ABS64`` relocation type is used for normal 64-bit data. +The actual to-be-relocated data is stored at ``r_offset`` and the read/write data +bitsize is 64 (8 bytes). The relocation can be resolved with +the symbol value plus implicit addend. + +Both ``R_BPF_64_ABS32`` and ``R_BPF_64_NODYLD32`` types are for 32-bit data. +But ``R_BPF_64_NODYLD32`` specifically refers to relocations in ``.BTF`` and +``.BTF.ext`` sections. For cases like bcc where llvm ``ExecutionEngine RuntimeDyld`` +is involved, ``R_BPF_64_NODYLD32`` types of relocations should not be resolved +to actual function/variable address. Otherwise, ``.BTF`` and ``.BTF.ext`` +become unusable by bcc and kernel. + +Type ``R_BPF_64_32`` is used for call instruction. The call target section +offset is stored at ``r_offset + 4`` (32bit) and calculated as +``(S + A) / 8 - 1``. + +Examples +======== + +Types ``R_BPF_64_64`` and ``R_BPF_64_32`` are used to resolve ``ld_imm64`` +and ``call`` instructions. For example:: + + __attribute__((noinline)) __attribute__((section("sec1"))) + int gfunc(int a, int b) { + return a * b; + } + static __attribute__((noinline)) __attribute__((section("sec1"))) + int lfunc(int a, int b) { + return a + b; + } + int global __attribute__((section("sec2"))); + int test(int a, int b) { + return gfunc(a, b) + lfunc(a, b) + global; + } + +Compiled with ``clang -target bpf -O2 -c test.c``, we will have +following code with `llvm-objdump -dr test.o``:: + + Disassembly of section .text: + + 0000000000000000 <test>: + 0: bf 26 00 00 00 00 00 00 r6 = r2 + 1: bf 17 00 00 00 00 00 00 r7 = r1 + 2: 85 10 00 00 ff ff ff ff call -1 + 0000000000000010: R_BPF_64_32 gfunc + 3: bf 08 00 00 00 00 00 00 r8 = r0 + 4: bf 71 00 00 00 00 00 00 r1 = r7 + 5: bf 62 00 00 00 00 00 00 r2 = r6 + 6: 85 10 00 00 02 00 00 00 call 2 + 0000000000000030: R_BPF_64_32 sec1 + 7: 0f 80 00 00 00 00 00 00 r0 += r8 + 8: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll + 0000000000000040: R_BPF_64_64 global + 10: 61 11 00 00 00 00 00 00 r1 = *(u32 *)(r1 + 0) + 11: 0f 10 00 00 00 00 00 00 r0 += r1 + 12: 95 00 00 00 00 00 00 00 exit + + Disassembly of section sec1: + + 0000000000000000 <gfunc>: + 0: bf 20 00 00 00 00 00 00 r0 = r2 + 1: 2f 10 00 00 00 00 00 00 r0 *= r1 + 2: 95 00 00 00 00 00 00 00 exit + + 0000000000000018 <lfunc>: + 3: bf 20 00 00 00 00 00 00 r0 = r2 + 4: 0f 10 00 00 00 00 00 00 r0 += r1 + 5: 95 00 00 00 00 00 00 00 exit + +The first relocation corresponds to ``gfunc(a, b)`` where ``gfunc`` has a value of 0, +so the ``call`` instruction offset is ``(0 + 0)/8 - 1 = -1``. +The second relocation corresponds to ``lfunc(a, b)`` where ``lfunc`` has a section +offset ``0x18``, so the ``call`` instruction offset is ``(0 + 0x18)/8 - 1 = 2``. +The third relocation corresponds to ld_imm64 of ``global``, which has a section +offset ``0``. + +The following is an example to show how R_BPF_64_ABS64 could be generated:: + + int global() { return 0; } + struct t { void *g; } gbl = { global }; + +Compiled with ``clang -target bpf -O2 -g -c test.c``, we will see a +relocation below in ``.data`` section with command +``llvm-readelf -r test.o``:: + + Relocation section '.rel.data' at offset 0x458 contains 1 entries: + Offset Info Type Symbol's Value Symbol's Name + 0000000000000000 0000000700000002 R_BPF_64_ABS64 0000000000000000 global + +The relocation says the first 8-byte of ``.data`` section should be +filled with address of ``global`` variable. + +With ``llvm-readelf`` output, we can see that dwarf sections have a bunch of +``R_BPF_64_ABS32`` and ``R_BPF_64_ABS64`` relocations:: + + Relocation section '.rel.debug_info' at offset 0x468 contains 13 entries: + Offset Info Type Symbol's Value Symbol's Name + 0000000000000006 0000000300000003 R_BPF_64_ABS32 0000000000000000 .debug_abbrev + 000000000000000c 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str + 0000000000000012 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str + 0000000000000016 0000000600000003 R_BPF_64_ABS32 0000000000000000 .debug_line + 000000000000001a 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str + 000000000000001e 0000000200000002 R_BPF_64_ABS64 0000000000000000 .text + 000000000000002b 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str + 0000000000000037 0000000800000002 R_BPF_64_ABS64 0000000000000000 gbl + 0000000000000040 0000000400000003 R_BPF_64_ABS32 0000000000000000 .debug_str + ...... + +The .BTF/.BTF.ext sections has R_BPF_64_NODYLD32 relocations:: + + Relocation section '.rel.BTF' at offset 0x538 contains 1 entries: + Offset Info Type Symbol's Value Symbol's Name + 0000000000000084 0000000800000004 R_BPF_64_NODYLD32 0000000000000000 gbl + + Relocation section '.rel.BTF.ext' at offset 0x548 contains 2 entries: + Offset Info Type Symbol's Value Symbol's Name + 000000000000002c 0000000200000004 R_BPF_64_NODYLD32 0000000000000000 .text + 0000000000000040 0000000200000004 R_BPF_64_NODYLD32 0000000000000000 .text |