Re: [PATCH v1 1/5] xsplice: Design document.

[Martin Pohlack <mpohlack@amazon.com>]

On 16.09.2015 23:01, Konrad Rzeszutek Wilk wrote:

[...]

> +### xsplice_patch
> +
> +This structure has the binary code (or data) to be patched. Depending on the
> +type it can either an inline patch (data or text) or require an relocation
> +change (which requires a trampoline). Naturally it also points to a blob
> +of the binary data to patch in, and the size of the patch.

On the Xen developer summit we agreed to start with a minimal approach
first.  Based on looking at the last ~50 XSA patches, I do think we can
do *without* the in-place patching and would propose to tackle this
approach later or not at all.

[...]

> +### Symbol names
> +
> +
> +Xen as it is now, has a couple of non-unique symbol names which will
> +make runtime symbol identification hard.  Sometimes, static symbols
> +simply have the same name in C files, sometimes such symbols get
> +included via header files, and some C files are also compiled
> +multiple times and linked under different names (guest_walk.c).
> +
> +As such we need to modify the linker to make sure that the symbol
> +table qualifies also symbols by their source file name.
> +
> +For the awkward situations in which C-files are compiled multiple
> +times patches we would need to some modification in the Xen code.
> +
> +
> +The convention for file-type symbols (that would allow to map many
> +symbols to their compilation unit) says that only the basename (i.e.,
> +without directories) is embedded.  This creates another layer of
> +confusion for duplicate file names in the build tree.
> +
> +That would have to be resolved.

Another approach here would be to qualify symbol names by the
object-file name which contains them + a unique path component, for example:

drivers/pci/pci.o
arch/x86/pci.o
arch/x86/x86_64/pci.o

> +
> +<pre>
> +> find . -name \*.c -print0 | xargs -0 -n1 basename | sort | uniq -c | sort -n | tail -n10
> +      3 shutdown.c
> +      3 sysctl.c
> +      3 time.c
> +      3 xenoprof.c
> +      4 gdbstub.c
> +      4 irq.c
> +      5 domain.c
> +      5 mm.c
> +      5 pci.c
> +      5 traps.c
> +</pre>

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