Browse zlib specs (39 of 62)

Proofs / zlib / Sizes and memory

res_free_inflate

The same for decompression, after one inflate call.

spec
66 lines of C
with its headers
106 lines
status
Proved
39 of 62
On this page

The spec

The spec is the C program harness/res_free_inflate.c, 66 lines, shown whole as it is in the repository at 37189f4. It includes harness/laws_common.h (40 lines). Its first comment states the property in full, with every bound.

C
// Law res_free_inflate: Counted through the zalloc and zfree it is given, inflate gives back every byte it took: when
// inflateInit2 with any windowBits (any int) fails, and after it succeeded, one inflate() of any input (under 2^32
// bytes) with any output space and flush, and inflateEnd, nothing is left allocated; and inflateInit2 and inflate
// return Z_MEM_ERROR only when the zalloc has returned Z_NULL.
#include "laws_common.h"

struct count {
	size_t now;
	size_t peak;
	int failed;
};
static voidpf counted_alloc(voidpf opaque, uInt items, uInt size) {
	struct count *count = opaque;
	size_t bytes = (size_t) items * size;
	size_t *block = malloc(sizeof (size_t) + bytes);
	if (block == NULL) {
		count->failed = 1;
		return Z_NULL;
	}
	block[0] = bytes;
	count->now += bytes;
	if (count->now > count->peak)
		count->peak = count->now;
	return block + 1;
}
static void counted_free(voidpf opaque, voidpf address) {
	struct count *count = opaque;
	size_t *block = (size_t *) address - 1;
	count->now -= block[0];
	free(block);
}
static void counted_stream(z_stream *strm, struct count *count) {
	count->now = 0;
	count->peak = 0;
	count->failed = 0;
	strm->zalloc = counted_alloc;
	strm->zfree = counted_free;
	strm->opaque = count;
	set_buffer(strm, Z_NULL, 0, Z_NULL, 0);
}

int main(void) {
	int window_bits = (int) nondet_u32();
	size_t input_len = nondet_u32();
	size_t room = nondet_u32();
	unsigned char *input = alloc_any_bytes(input_len);
	unsigned char *out = malloc(room);
	if (input == NULL || out == NULL)
		return 0;
	struct count count;
	z_stream strm;
	counted_stream(&strm, &count);

	int code = inflateInit2(&strm, window_bits);
	if (code == Z_OK) {
		set_buffer(&strm, input, input_len, out, room);
		code = inflate(&strm, (int) nondet_u32());
		inflateEnd(&strm);
	}

	// zlib.h, inflateInit2 and inflate: "Z_MEM_ERROR if there was not enough memory"; inflateEnd: "All dynamically
	// allocated data structures for this stream are freed."
	gp_assert(code != Z_MEM_ERROR || count.failed);
	gp_assert(count.now == 0);
	return 0;
}
harness/laws_common.h, 40 lines
C
// laws_common.h: trivial helpers shared by the zlib laws (each law includes it once). No models, no algorithms.
#include <limits.h>
#include <stdlib.h>
#include "quickproof.h"
#include "zlib.h"
static size_t upto(size_t max) {
	size_t value = nondet_size();
	return value < max ? value : max;
}
static uInt clip(size_t n) { return n < UINT_MAX ? (uInt) n : UINT_MAX; }
static unsigned char *alloc_any_bytes(size_t n) {
	unsigned char *bytes = malloc(n);
	if (bytes != NULL)
		nondet_bytes(bytes, n);
	return bytes;
}
static unsigned char *copy_of(const unsigned char *source, size_t n) {
	unsigned char *copy = malloc(n);
	for (size_t i = 0; copy != NULL && i < n; i++)
		copy[i] = source[i];
	return copy;
}
static int bytes_eq(const unsigned char *a, const unsigned char *b, size_t n) {
	for (size_t i = 0; i < n; i++)
		if (a[i] != b[i])
			return 0;
	return 1;
}
static void set_buffer(z_stream *strm, unsigned char *in, size_t in_len, unsigned char *out, size_t out_len) {
	strm->next_in = in;
	strm->avail_in = (uInt) in_len;
	strm->next_out = out;
	strm->avail_out = (uInt) out_len;
}
static void new_stream(z_stream *strm) {
	strm->zalloc = Z_NULL;
	strm->zfree = Z_NULL;
	strm->opaque = Z_NULL;
	set_buffer(strm, Z_NULL, 0, Z_NULL, 0);
}

The theorem

QuickProof generated this statement from the spec, in src/contracts/res_free_inflate.v:

Rocq
Theorem res_free_inflate : harness_safe whole_prog.

src/contracts/laws.v states it on the spec's own program, whole_prog (the spec linked with the code under test), with its proof:

Rocq
Theorem res_free_inflate : harness_safe Zlib.contracts.res_free_inflate.whole_prog.
Proof. exact (proj1 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 (proj2 Zlib.contracts.suite.suite)))))))))))))))))))). Qed.

Read as a statement about runs, it says that no run of the program has undefined behaviour or a failing check, for every value the spec can draw. That reading rests on VST's adequacy theorem, which is not yet instantiated in Rocq (formerly Coq) for QuickProof's environment.

The C files (units) its program links
  • adler32.c
  • crc32.c
  • inflate.c
  • inffast.c
  • inftrees.c
  • zutil.c
  • quickproof/libc/libc.c

What it leaves out

  • What the first comment of the spec excludes, and its bounds.
  • Like every spec of this proof: termination (a run that never returns is not a counterexample), and binaries built by a compiler (the theorem is about the code as CompCert defines C for x86_64, LP64), one thread.
  • Where zlib reports Z_MEM_ERROR, most specs end the run and claim nothing about it; the first comment of the spec says so.
  • The edits to zlib's code, listed in the repository, are tested, not proved.

The summary page says what the proof as a whole covers.

How it was proved

AI agents wrote the proof, and Rocq checks it. qp verify passes on this repository: this statement is the one generated from the spec at the contract commit, and its proof uses only Rocq's standard axioms and VST's abstract malloc library.