Re: [PATCH v5 0/8] Remove gdbserver dependency on xml files

[Simon Marchi <simark@simark.ca>]

On 2018-04-10 10:33 AM, Alan Hayward wrote:
> V5 addresses Simon's review comments, mostly in the first two patches and the
> "Create xml..." patch. Added changes since previous verion in the patch
> headers. Series is slightly shorted as some early patches have been committed.
> 
> Summary:
> 
> For those targets that use new style target descriptions (also known as
> flexible target descriptions), this set of patches removes the dependency on
> xml files. Namely:
> * Removes inclusion of xml files within gdbserver.
> * Removes the requirement for the .c files in features/ to be generated from
> cached xml files.
> This is made possible by changing xml descriptions generated by gdbserver, so
> that instead of including xml file names, gdbserver now generate a complete
> xml description.
> 
> The second point will be required for aarch64 SVE support, where the register
> size are variable. Creating SVE xml files for every possible vector length
> would not be feasible. Instead the plan for aarch64 SVE is to hand write the
> features/ .c code that would normally be generated from xml.
> 
> Targets which use the older style target descriptions have not been changed.
> 
> 
> XML Generation:
> 
> In existing code, gdbserver uses C code auto generated from xml files to
> create target descriptions. When sending an xml description to GDB, the
> function tdesc_get_features_xml () creates an xml containing the name of the
> original xml file(s). For example:
> 
> <!DOCTYPE target SYSTEM "gdb-target.dtd">
> <target>
>   <architecture>i386</architecture>
>   <osabi>GNU/Linux</osabi>
>   <xi:include href="32bit-core.xml"/>
>   <xi:include href="32bit-sse.xml"/>
>   <xi:include href="32bit-linux.xml"/>
>   <xi:include href="32bit-avx.xml"/>
> </target>
> 
> Upon receipt, GDB then makes requests to gdbserver for the contents of the
> xml files. Gdbserver keeps full copies all the xml files inside the binary.
> 
> This patch series adds common code that allows gdbserver (and gdb) to turn
> a C target description structure into xml.
> Now when asked fort an xml description to gdb, gdbserver turns the entire
> target description structure back into xml, without using any cached files.
> Producing, for example:
> 
> <!DOCTYPE target SYSTEM "gdb-target.dtd">
> <target>
>   <architecture>i386</architecture>
>   <osabi>GNU/Linux</osabi>
>   <feature name="org.gnu.gdb.i386.core">
>     <flags id="i386_eflags" size="4">
>       <field name="CF" start="0" end="0"/>
>       <field name="" start="1" end="1"/>
>       <field name="PF" start="2" end="2"/>
>       <field name="AF" start="4" end="4"/>
> ...etc...
> 
> 
> Patch Contents:
> 
> Patches 1-3 commonise the various target descriptor functionality, allowing
> gdbserver to parse target descriptions in the same way as gdb. This series
> does not commonise target_desc, but this is hopefully a long term goal.
> 
> The sixth patch adds the xml printer, which iterates through the parsing
> generated in the previous patches.
> 
> The other patches are clean up patches.
> 
> Patches have been tested on a make check on x86 targets=all build with
> target boards unix and native-gdbserver. Also built and tested aarch64 and
> Arm32 (which uses old style descriptions)
> In addition, new test cases are added to the unit tests.

Hi Alan,

Thanks a lot for this writeup, it was very useful to get back in the subject,
since a few weeks is enough for me to forget everything I learned last time :)
Seriously, it helps a lot, and I'm sure it will be a good reference in the
future.

I replied to some patches, those I have not replied to LGTM.  I think that with
those little fixes, this series is ready to go in (as far as my target description
knowledge goes).

Simon