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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
| commit | f4cdf7ca9a1fdcca413157df19753f388a5a224e (patch) | |
| tree | 60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/bpf/linux-notes.rst | |
| download | linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip | |
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab:
- v4l2-core: added ISP statistics support and per-block validation
- v4l2-core: Allow unknown HDR10 white point and luminance
- New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor
- New codec: Milos: VPU v2.0 codec support
- isp driver: gained support for Dreamchip RPPX1 ISP framework
- vsp1 driver: gained support for RZ/T2H and RZ/N2H
- Novalake driver: gained CVS support for new NVL hardware
- dvb-core: fix feed leak on failed DMX_ADD_PID
- several driver fixes, cleanups and minor improvements
* tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits)
media: ipu-bridge: check all DMI entries when overriding sensor rotation
media: v4l2-async: avoid deleting unlinked ASC entry on link error
media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement
media: intel/ipu6: fix async notifier cleanup leak on parse error
media: staging/ipu7: fix async notifier UAF on probe error path
media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path
media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem()
media: rcar-isp: Fix VSPX reference leaks
media: rcar-isp: Release ISPCORE resources
media: i2c: imx415: Release runtime PM reference on VBLANK error
media: i2c: imx415: Return test pattern write errors
media: renesas: vsp1: Declare index variables in for loop statement
media: renesas: vsp1: Make reset control optional to support platforms without a reset line
media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs
media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs
media: nxp: imx8-isi: Add additional 32-bit RGB format support
media: nxp: imx8-isi: Add 16-bit raw Bayer format support
media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams
media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks
media: nxp: imx8-isi: Correct color map between V4L2 and ISI
...
Diffstat (limited to 'Documentation/bpf/linux-notes.rst')
| -rw-r--r-- | Documentation/bpf/linux-notes.rst | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst new file mode 100644 index 000000000..00d2693de --- /dev/null +++ b/Documentation/bpf/linux-notes.rst @@ -0,0 +1,84 @@ +.. contents:: +.. sectnum:: + +========================== +Linux implementation notes +========================== + +This document provides more details specific to the Linux kernel implementation of the eBPF instruction set. + +Byte swap instructions +====================== + +``BPF_FROM_LE`` and ``BPF_FROM_BE`` exist as aliases for ``BPF_TO_LE`` and ``BPF_TO_BE`` respectively. + +Jump instructions +================= + +``BPF_CALL | BPF_X | BPF_JMP`` (0x8d), where the helper function +integer would be read from a specified register, is not currently supported +by the verifier. Any programs with this instruction will fail to load +until such support is added. + +Maps +==== + +Linux only supports the 'map_val(map)' operation on array maps with a single element. + +Linux uses an fd_array to store maps associated with a BPF program. Thus, +map_by_idx(imm) uses the fd at that index in the array. + +Variables +========= + +The following 64-bit immediate instruction specifies that a variable address, +which corresponds to some integer stored in the 'imm' field, should be loaded: + +========================= ====== === ========================================= =========== ============== +opcode construction opcode src pseudocode imm type dst type +========================= ====== === ========================================= =========== ============== +BPF_IMM | BPF_DW | BPF_LD 0x18 0x3 dst = var_addr(imm) variable id data pointer +========================= ====== === ========================================= =========== ============== + +On Linux, this integer is a BTF ID. + +Legacy BPF Packet access instructions +===================================== + +As mentioned in the `ISA standard documentation +<instruction-set.html#legacy-bpf-packet-access-instructions>`_, +Linux has special eBPF instructions for access to packet data that have been +carried over from classic BPF to retain the performance of legacy socket +filters running in the eBPF interpreter. + +The instructions come in two forms: ``BPF_ABS | <size> | BPF_LD`` and +``BPF_IND | <size> | BPF_LD``. + +These instructions are used to access packet data and can only be used when +the program context is a pointer to a networking packet. ``BPF_ABS`` +accesses packet data at an absolute offset specified by the immediate data +and ``BPF_IND`` access packet data at an offset that includes the value of +a register in addition to the immediate data. + +These instructions have seven implicit operands: + +* Register R6 is an implicit input that must contain a pointer to a + struct sk_buff. +* Register R0 is an implicit output which contains the data fetched from + the packet. +* Registers R1-R5 are scratch registers that are clobbered by the + instruction. + +These instructions have an implicit program exit condition as well. If an +eBPF program attempts access data beyond the packet boundary, the +program execution will be aborted. + +``BPF_ABS | BPF_W | BPF_LD`` (0x20) means:: + + R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + imm)) + +where ``ntohl()`` converts a 32-bit value from network byte order to host byte order. + +``BPF_IND | BPF_W | BPF_LD`` (0x40) means:: + + R0 = ntohl(*(u32 *) ((struct sk_buff *) R6->data + src + imm)) |
