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authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /Documentation/bpf/llvm_reloc.rst
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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(). ...
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+.. 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