prog, pkg/compiler: add `BufferCompressed` buffer type & `compressed_image` builtin

Create the `BufferCompressed` kind of `BufferType`, which will be used
to represent compressed data. Create the corresponding `compressed_image`
syzlang builtin, which is backed by `BufferCompressed`. For now, no
syscalls use this feature - this will be introduced in future commits.

We have to be careful to decompress the data before mutating, and
re-compress before storing. We make sure that any deserialised
`BufferCompressed` data is valid too.

`BufferCompressed` arguments are mutated using a generic heatmap. In
future, we could add variants of `BufferCompressed` or populate the
`BufferType` sub-kind, using it to choose different kinds of heatmap for
different uncompressed data formats.

Various operations on compressed data must be forbidden, so we check for
`BufferCompressed` in key places. We also have to ensure `compressed_image`
can only be used in syscalls that are marked `no_{generate,minimize}`.
Therefore, we add a generic compiler check which allows type
descriptions to require attributes on the syscalls which use them.

1 files changed, 5 insertions, 0 deletions

diff --git a/prog/hints.go b/prog/hints.go
index c66242357..ef7ee17a5 100644
--- a/prog/hints.go
+++ b/prog/hints.go
@@ -109,6 +109,11 @@ func generateHints(compMap CompMap, arg Arg, exec func()) {
 				// (and filter out file names).
 				return
 			}
+		case BufferCompressed:
+			// We can reconsider this in the future, e.g. by decompressing, applying
+			// hints, then re-compressing. We will need to ensure this doesn't
+			// produce too many mutants given the current handling of buffers.
+			return
 		}
 	}