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Puranjay Mohan says: ==================== Signed loads from Arena Changelog: v3 -> v4: v3: https://lore.kernel.org/all/20250915162848.54282-1-puranjay@kernel.org/ - Update bpf_jit_supports_insn() in riscv jit to reject signed arena loads (Eduard) - Fix coding style related to braces usage in an if statement in x86 jit (Eduard) v2 -> v3: v2: https://lore.kernel.org/bpf/20250514175415.2045783-1-memxor@gmail.com/ - Fix encoding for the generated instructions in x86 JIT (Eduard) The patch in v2 was generating instructions like: 42 63 44 20 f8 movslq -0x8(%rax,%r12), %eax This doesn't make sense because movslq outputs a 64-bit result, but the destination register here is set to eax (32-bit). The fix it to set the REX.W bit in the opcode, that means changing EMIT2(add_3mod(0x40, ...)) to EMIT2(add_3mod(0x48, ...)) - Add arm64 support - Add selftests signed laods from arena. v1 -> v2: v1: https://lore.kernel.org/bpf/20250509194956.1635207-1-memxor@gmail.com - Use bpf_jit_supports_insn. (Alexei) Currently, signed load instructions into arena memory are unsupported. The compiler is free to generate these, and on GCC-14 we see a corresponding error when it happens. The hurdle in supporting them is deciding which unused opcode to use to mark them for the JIT's own consumption. After much thinking, it appears 0xc0 / BPF_NOSPEC can be combined with load instructions to identify signed arena loads. Use this to recognize and JIT them appropriately, and remove the verifier side limitation on the program if the JIT supports them. ==================== Link: https://patch.msgid.link/20250923110157.18326-1-puranjay@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.