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In fill_thread_core_info() the ptrace accessible registers are collected for a core file to be written out as notes. The note array is allocated from a size calculated by iterating the user regset view, and counting the regsets that have a non-zero core_note_type. However, this only allows for there to be non-zero core_note_type at the end of the regset view. If there are any in the middle, fill_thread_core_info() will overflow the note allocation, as it iterates over the size of the view and the allocation would be smaller than that. To apparently avoid this problem, x86_32_regsets and x86_64_regsets need to be constructed in a special way. They both draw their indices from a shared enum x86_regset, but 32 bit and 64 bit don't all support the same regsets and can be compiled in at the same time in the case of IA32_EMULATION. So this enum has to be laid out in a special way such that there are no gaps for both x86_32_regsets and x86_64_regsets. This involves ordering them just right by creating aliases for enum’s that are only in one view or the other, or creating multiple versions like REGSET32_IOPERM/REGSET64_IOPERM. So the collection of the registers tries to minimize the size of the allocation, but it doesn’t quite work. Then the x86 ptrace side works around it by constructing the enum just right to avoid a problem. In the end there is no functional problem, but it is somewhat strange and fragile. It could also be improved like this [1], by better utilizing the smaller array, but this still wastes space in the regset array’s if they are not carefully crafted to avoid gaps. Instead, just fully separate out the enums and give them separate 32 and 64 enum names. Add some bitsize-free defines for REGSET_GENERAL and REGSET_FP since they are the only two referred to in bitsize generic code. While introducing a bunch of new 32/64 enums, change the pattern of the name from REGSET_FOO32 to REGSET32_FOO to better indicate that the 32 is in reference to the CPU mode and not the register size, as suggested by Eric Biederman. This should have no functional change and is only changing how constants are generated and referred to. [1] https://lore.kernel.org/lkml/20180717162502.32274-1-yu-cheng.yu@intel.com/ Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lore.kernel.org/all/20221021221803.10910-2-rick.p.edgecombe%40intel.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.