syz-kconf: execute shell snippets in reverse loading order

Background:
- syz-kconf loads and overlays config fragments to form a final kernel
  config. Fragments are loaded top to bottom as defined in the includes
  section of main.yml or your downstream syz-kconf config.
- A config fragment loaded later can override kconf options set by an
  earlier loaded fragment. However the override keyword can only be used
  if an earlier fragment really did set the same option. Otherweise an
  error is raised.
- With this in mind it makes sense to load fragments from broadest scope
  to most specific e.g. base -> x86_64 -> chromeos, so that chromeos can
  override a setting usually enabled on x86_64 machines.

The Problem:
- Before this change shell snippets were executed in order they were
  loaded from the fragments.
- This is unfortunate as the broad fragments like x86_64.yml expect to
  operate on an existing .config with their shell snippets. Meanwhile
  some downstream distros like icebreaker generate their config using
  such a shell snippet.
- Hence ordering the fragments like base -> x86_64 -> icebreaker results
  in an error about the x86_64 not finding a .config without this
  change. Meanwhile ordering icebreaker -> base -> x86_64 works, but
  means the icebreaker fragment can't override x86_64 kconf options.

The Solution:
- This change resolves the problem outlined above by reversing the order
  shell snippets are executed. Now shell snippets will be executed
  starting with the most recently loaded fragment. This way the proposed
  fragment order base -> x86_64 -> icebreaker becomes viable.
- Luckily the shell section isn't heavily used, so this change didn't
  result in meaningfull final config changes.

1 files changed, 3 insertions, 1 deletions

diff --git a/tools/syz-kconf/parser.go b/tools/syz-kconf/parser.go
index 00455c3e5..b2ac82e74 100644
--- a/tools/syz-kconf/parser.go
+++ b/tools/syz-kconf/parser.go
@@ -197,16 +197,18 @@ func mergeFile(inst *Instance, raw *rawFile, file string, errs *Errors) {
 		}
 		inst.Linker = raw.Linker
 	}
+	prependShell := []Shell{}
 	for _, node := range raw.Shell {
 		cmd, _, constraints, err := parseNode(node)
 		if err != nil {
 			errs.push("%v:%v: %v", file, node.Line, err)
 		}
-		inst.Shell = append(inst.Shell, Shell{
+		prependShell = append(prependShell, Shell{
 			Cmd:         cmd,
 			Constraints: constraints,
 		})
 	}
+	inst.Shell = append(prependShell, inst.Shell...)
 	if raw.Verbatim != "" {
 		inst.Verbatim = append(append(inst.Verbatim, strings.TrimSpace(raw.Verbatim)...), '\n')
 	}