portability of ShellPkg

[Leif Lindholm <leif.lindholm@linaro.org>]

Hi all,

(This is partly a summary of discussions that have been held on IRC
and offline, with Alex Graf and Mike Kinney.)

The UEFI Shell, as produced by the contents of ShellPkg, is needed for
running the UEFI SCT. This has never been problematic before - but now
we are starting to run SCT on the U-Boot implementation of the UEFI
interfaces, certain implicit assumptions may need to be made explicit,
and perhaps reevaluated.

My feeling is the following:
- The MinUefiShell variant should be sufficient to run SCT.
- The UEFI Shell as provided by ShellPkg (any flavour) should run on
  any valid UEFI implementation. Where underlying functionality is
  missing for certain commands, those commands should be
  degraded/disabled to let remaining commands function.

Ideally, I would like to see a Readme.md in ShellPkg, basically
providing a mission statement. I could write one, but I expect the
people who actually maintain it would be better suited :)

We currently have an issue with running the shell on U-Boot because
even MinUefiShell pulls in UefiShellDebug1CommandsLib.inf. This
appears to be inadvertent, since it is also included a few lines
further down inside an !ifndef $(NO_SHELL_PROFILES) guard.
So I would propose the following patch (and can send it out properly
if the maintainers agree):

diff --git a/ShellPkg/ShellPkg.dsc b/ShellPkg/ShellPkg.dsc
index 59dd07e0ae..c852abd3f7 100644
--- a/ShellPkg/ShellPkg.dsc
+++ b/ShellPkg/ShellPkg.dsc
@@ -101,7 +101,6 @@ [Components]
   ShellPkg/Library/UefiShellLevel3CommandsLib/UefiShellLevel3CommandsLib.inf
   ShellPkg/Library/UefiShellDriver1CommandsLib/UefiShellDriver1CommandsLib.inf
   ShellPkg/Library/UefiShellInstall1CommandsLib/UefiShellInstall1CommandsLib.inf
-  ShellPkg/Library/UefiShellDebug1CommandsLib/UefiShellDebug1CommandsLib.inf
   ShellPkg/Library/UefiShellNetwork1CommandsLib/UefiShellNetwork1CommandsLib.inf
   ShellPkg/Library/UefiShellNetwork2CommandsLib/UefiShellNetwork2CommandsLib.inf
		  
The reason this causes a problem is because this module has a
dependency on HobLib, which ASSERTS if it does not find any HOBs lying
around. Since HOBs are a PI concept rather than a UEFI concept,
ideally we would not terminate the shell if they are missing. However,
since the HobLib is generic to EDK2, we also shouldn't just go
stripping ASSERTs out of it. The above patch gives us a way of
unblocking the SCT on U-Boot UEFI while we consider what to do about
the bigger question.

Thoughts?

/
    Leif