Heads up: gcc miscompiling initramfs zlib decompression code at -O3

[Heiko Carstens]

On Mon, May 03, 2021 at 10:41:45AM -0700, Linus Torvalds wrote:
> It would be lovely if somebody also took a look at some of the other
> zlib code, like inflate.c itself. But some of that code has rather
> subtle changes for things like s390 hardware support, and we have
> thihngs like our fallthrough rules etc, so it gets a bit hairier.
> 
> Which is why I did just this fairly minimal part.
> 
> Note that the commit message has a "Not-yet-signed-off-by:" from me.
> That's purely because I wanted it to be obvious that this needs a lot
> more testing - I'm not comfy with this patch unless somebody takes it
> upon themselves to actually test it under different loads (and
> different architectures).

The patch below is required on top of your patch to make it compile
for s390 as well.
Tested with kernel image decompression, and also btrfs with file
compression; both software and hardware compression.
Everything seems to work.

diff --git a/lib/zlib_dfltcc/dfltcc_inflate.c b/lib/zlib_dfltcc/dfltcc_inflate.c
index fb60b5a6a1cb..3bb3e431b79f 100644
--- a/lib/zlib_dfltcc/dfltcc_inflate.c
+++ b/lib/zlib_dfltcc/dfltcc_inflate.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: Zlib
 
+#include <linux/zlib.h>
+#include "../zlib_inflate/inftrees.h"
 #include "../zlib_inflate/inflate.h"
 #include "dfltcc_util.h"
 #include "dfltcc.h"
@@ -122,7 +124,7 @@ dfltcc_inflate_action dfltcc_inflate(
     param->cvt = CVT_ADLER32;
     param->sbb = state->bits;
     param->hl = state->whave; /* Software and hardware history formats match */
-    param->ho = (state->write - state->whave) & ((1 << HB_BITS) - 1);
+    param->ho = (state->wnext - state->whave) & ((1 << HB_BITS) - 1);
     if (param->hl)
         param->nt = 0; /* Honor history for the first block */
     param->cv = state->check;
@@ -137,7 +139,7 @@ dfltcc_inflate_action dfltcc_inflate(
     state->last = cc == DFLTCC_CC_OK;
     state->bits = param->sbb;
     state->whave = param->hl;
-    state->write = (param->ho + param->hl) & ((1 << HB_BITS) - 1);
+    state->wnext = (param->ho + param->hl) & ((1 << HB_BITS) - 1);
     state->check = param->cv;
     if (cc == DFLTCC_CC_OP2_CORRUPT && param->oesc != 0) {
         /* Report an error if stream is corrupted */
diff --git a/lib/zlib_inflate/inflate.h b/lib/zlib_inflate/inflate.h
index 6ece8efd879b..52314b8b28ea 100644
--- a/lib/zlib_inflate/inflate.h
+++ b/lib/zlib_inflate/inflate.h
@@ -1,3 +1,6 @@
+#ifndef __ZLIB_INFLATE_INFLATE_H
+#define __ZLIB_INFLATE_INFLATE_H
+
 /* inflate.h -- internal inflate state definition
  * Copyright (C) 1995-2016 Mark Adler
  * For conditions of distribution and use, see copyright notice in zlib.h
@@ -123,3 +126,5 @@ struct inflate_state {
     int back;                   /* bits back of last unprocessed length/lit */
     unsigned was;               /* initial length of match */
 };
+
+#endif /* __ZLIB_INFLATE_INFLATE_H */
diff --git a/lib/zlib_inflate/inftrees.h b/lib/zlib_inflate/inftrees.h
index fe4307fcfbe3..39d5d90d1258 100644
--- a/lib/zlib_inflate/inftrees.h
+++ b/lib/zlib_inflate/inftrees.h
@@ -1,3 +1,6 @@
+#ifndef __ZLIB_INFLATE_INFTREES_H
+#define __ZLIB_INFLATE_INFTREES_H
+
 /* inftrees.h -- header to use inftrees.c
  * Copyright (C) 1995-2005, 2010 Mark Adler
  * For conditions of distribution and use, see copyright notice in zlib.h
@@ -60,3 +63,5 @@ typedef enum {
 int zlib_inflate_table (codetype type, unsigned short *lens,
                              unsigned codes, code **table,
                              unsigned *bits, unsigned short *work);
+
+#endif /* __ZLIB_INFLATE_INFTREES_H */