Fix full memory dumps on amd64 #1706
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Provide the kernel's physical address in an ELF section when doing a full memory dump on amd64. This allows libkvm to figure out where the kernel was loaded in physical memory. Signed-off-by: Ahmad Khalifa <[email protected]>
amd64 kernels don't have to be loaded at 2M physical anymore, they can be anywhere in the lower 4G of the physical address space. The kernel now provides its physical address in an ELF section in the dump, so account for it. Signed-off-by: Ahmad Khalifa <[email protected]>
Starting 13.1 the amd64 kernel was made relocatable, but the kernel didn't provide enough information for libkvm to figure out where it was loaded. Signed-off-by: Ahmad Khalifa <[email protected]>
VexedUXR
commented
May 23, 2025
| nl[1].n_name = 0; | ||
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| /* XXX | ||
| * Relocatable kernels can still be loaded at 2M. |
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Kernels loaded with copy_staging enabled in the loader (which isn't the default) will still be at 2M. There doesn't seem to be a way to detect if they were actually loaded there though.
The only way to read such dumps seems to be to read the dump anyways, at the risk of reading garbage.
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Currently, libkvm can't read full memory dumps correctly on amd64 since it assumes the kernel was loaded at 2M physical. Fix this by adding the kernel's physical address in an auxiliary ELF section, similar to what arm does.
This seems to have been broken since 13.1 (see 8ca493f and 1b33aa1), so document that.
From my testing, this also stops kgdb and lldb from crashing when trying to open full memory dumps.