3.6. GDB step debug userland processes
QEMU’s -gdb GDB breakpoints are set on virtual addresses, so you can in theory debug userland processes as well.
You will generally want to use gdbserver for this as it is more reliable, but this method can overcome the following limitations of gdbserver:
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the emulator does not support host to guest networking. This seems to be the case for gem5 as explained at: Section 15.3.1.3, “gem5 host to guest networking”
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cannot see the start of the
initprocess easily -
gdbserveralters the working of the kernel, and makes your run less representative
Known limitations of direct userland debugging:
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the kernel might switch context to another process or to the kernel itself e.g. on a system call, and then TODO confirm the PIC would go to weird places and source code would be missing.
Solutions to this are being researched at: Section 3.10.1, “lx-ps”.
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TODO step into shared libraries. If I attempt to load them explicitly:
(gdb) sharedlibrary ../../staging/lib/libc.so.0 No loaded shared libraries match the pattern `../../staging/lib/libc.so.0'.
since GDB does not know that libc is loaded.