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reading, and one bug in the new RegisterContextUnifiedCore class.
The PR I landed a few days ago to allow Mach-O corefiles to augment
their registers with additional per-thread registers in metadata exposed
a few bugs in the x86_64 corefile reader when running under different CI
environments. It also showed a bug in my RegisterContextUnifiedCore
class where I wasn't properly handling lookups of unknown registers
(e.g. the LLDB_GENERIC_RA when debugging an intel target).
The Mach-O x86_64 corefile support would say that it had fpu & exc
registers available in every corefile, regardless of whether they were
actually present. It would only read the bytes for the first register
flavor in the LC_THREAD, the GPRs, but it read them incorrectly, so
sometimes you got more register context than you'd expect. The LC_THREAD
register context specifies a flavor and the number of uint32_t words;
the ObjectFileMachO method would read that number of uint64_t's,
exceeding the GPR register space, but it was followed by FPU and then
EXC register space so it didn't crash. If you had a corefile with GPR
and EXC register bytes, it would be written into the GPR and then FPU
register areas, with zeroes filling out the rest of the context.
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The "process metadata" LC_NOTE allows for thread IDs to be specified in
a Mach-O corefile. This extends the JSON recognzied in that LC_NOTE to
allow for additional registers to be supplied on a per-thread basis.
The registers included in a Mach-O corefile LC_THREAD load command can
only be one of the register flavors that the kernel (xnu) defines in
<mach/arm/thread_status.h> for arm64 -- the general purpose registers,
floating point registers, exception registers.
JTAG style corefile producers may have access to many additional
registers beyond these that EL0 programs typically use, for instance
TCR_EL1 on AArch64, and people developing low level code need access to
these registers. This patch defines a format for including these
registers for any thread.
The JSON in "process metadata" is a dictionary that must have a
`threads` key. The value is an array of entries, one per LC_THREAD in
the Mach-O corefile. The number of entries must match the LC_THREADs so
they can be correctly associated.
Each thread's dictionary must have two keys, `sets`, and `registers`.
`sets` is an array of register set names. If a register set name matches
one from the LC_THREAD core registers, any registers that are defined
will be added to that register set. e.g. metadata can add a register to
the "General Purpose Registers" set that lldb shows users.
`registers` is an array of dictionaries, one per register. Each register
must have the keys `name`, `value`, `bitsize`, and `set`. It may provide
additional keys like `alt-name`, that
`DynamicRegisterInfo::SetRegisterInfo` recognizes.
This `sets` + `registers` formatting is the same that is used by the
`target.process.python-os-plugin-path` script interface uses, both are
parsed by `DynamicRegisterInfo`. The one addition is that in this
LC_NOTE metadata, each register must also have a `value` field, with the
value provided in big-endian base 10, as usual with JSON.
In RegisterContextUnifiedCore, I combine the register sets & registers
from the LC_THREAD for a specific thread, and the metadata sets &
registers for that thread from the LC_NOTE. Even if no LC_NOTE is
present, this class ingests the LC_THREAD register contexts and
reformats it to its internal stores before returning itself as the
RegisterContex, instead of shortcutting and returning the core's native
RegisterContext. I could have gone either way with that, but in the end
I decided if the code is correct, we should live on it always.
I added a test where we process save-core to create a userland corefile,
then use a utility "add-lcnote" to strip the existing "process metadata"
LC_NOTE that lldb put in it, and adds a new one from a JSON string.
rdar://74358787
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Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>
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