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91f658587a
This patch fixes issues with stackframe unwinding and alignment in the current stack layout for BPF programs on RV32. In the current layout, RV32 fp points to the JIT scratch registers, rather than to the callee-saved registers. This breaks stackframe unwinding, which expects fp to point just above the saved ra and fp registers. This patch fixes the issue by moving the callee-saved registers to be stored on the top of the stack, pointed to by fp. This satisfies the assumptions of stackframe unwinding. This patch also fixes an issue with the old layout that the stack was not aligned to 16 bytes. Stacktrace from JITed code using the old stack layout: [ 12.196249 ] [<c0402200>] walk_stackframe+0x0/0x96 Stacktrace using the new stack layout: [ 13.062888 ] [<c0402200>] walk_stackframe+0x0/0x96 [ 13.063028 ] [<c04023c6>] show_stack+0x28/0x32 [ 13.063253 ] [<a403e778>] bpf_prog_82b916b2dfa00464+0x80/0x908 [ 13.063417 ] [<c09270b2>] bpf_test_run+0x124/0x39a [ 13.063553 ] [<c09276c0>] bpf_prog_test_run_skb+0x234/0x448 [ 13.063704 ] [<c048510e>] __do_sys_bpf+0x766/0x13b4 [ 13.063840 ] [<c0485d82>] sys_bpf+0xc/0x14 [ 13.063961 ] [<c04010f0>] ret_from_syscall+0x0/0x2 The new code is also simpler to understand and includes an ASCII diagram of the stack layout. Tested on riscv32 QEMU virt machine. Signed-off-by: Luke Nelson <luke.r.nels@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Xi Wang <xi.wang@gmail.com> Link: https://lore.kernel.org/bpf/20200430005127.2205-1-luke.r.nels@gmail.com |
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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 Restructured Text 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.