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Its possible to have divergent ALU32 and ALU64 bounds when using JMP32 instructins and ALU64 arithmatic operations. Sometimes the clang will even generate this code. Because the case is a bit tricky lets add a specific test for it. Here is pseudocode asm version to illustrate the idea, 1 r0 = 0xffffffff00000001; 2 if w0 > 1 goto %l[fail]; 3 r0 += 1 5 if w0 > 2 goto %l[fail] 6 exit The intent here is the verifier will fail the load if the 32bit bounds are not tracked correctly through ALU64 op. Similarly we can check the 64bit bounds are correctly zero extended after ALU32 ops. 1 r0 = 0xffffffff00000001; 2 w0 += 1 2 if r0 > 3 goto %l[fail]; 6 exit The above will fail if we do not correctly zero extend 64bit bounds after 32bit op. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/158560430155.10843.514209255758200922.stgit@john-Precision-5820-Tower
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.