From 08c708015ec372b6c28d341cba7bbc86843cc17b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Wed, 14 Sep 2022 11:40:09 +0300
Subject: tools: Allocate the priv structs with proper alignment

Previously, they could be allocated with any random alignment
matching the end of the MuxerContext/DemuxerContext. The
priv structs themselves can have members that require specific
alignment, or at least the default alignment of malloc()/calloc()
(which is sufficient for native types such as uint64_t and
doubles).

This fixes crashes in some arm builds, where GCC (correctly) wants
to use 64 bit aligned stores to write to MD5Context.
---
 tools/input/input.c   | 5 +++--
 tools/output/output.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/input/input.c b/tools/input/input.c
index 4756648..2dfaa97 100644
--- a/tools/input/input.c
+++ b/tools/input/input.c
@@ -41,6 +41,7 @@
 struct DemuxerContext {
     DemuxerPriv *data;
     const Demuxer *impl;
+    uint64_t priv_data[];
 };
 
 extern const Demuxer ivf_demuxer;
@@ -109,12 +110,12 @@ int input_open(DemuxerContext **const c_out,
         }
     }
 
-    if (!(c = calloc(1, sizeof(DemuxerContext) + impl->priv_data_size))) {
+    if (!(c = calloc(1, offsetof(DemuxerContext, priv_data) + impl->priv_data_size))) {
         fprintf(stderr, "Failed to allocate memory\n");
         return DAV1D_ERR(ENOMEM);
     }
     c->impl = impl;
-    c->data = (DemuxerPriv *) &c[1];
+    c->data = (DemuxerPriv *) c->priv_data;
     if ((res = impl->open(c->data, filename, fps, num_frames, timebase)) < 0) {
         free(c);
         return res;
diff --git a/tools/output/output.c b/tools/output/output.c
index cf66d2e..f8910d4 100644
--- a/tools/output/output.c
+++ b/tools/output/output.c
@@ -46,6 +46,7 @@ struct MuxerContext {
     unsigned fps[2];
     const char *filename;
     int framenum;
+    uint64_t priv_data[];
 };
 
 extern const Muxer null_muxer;
@@ -123,12 +124,12 @@ int output_open(MuxerContext **const c_out,
         }
     }
 
-    if (!(c = malloc(sizeof(MuxerContext) + impl->priv_data_size))) {
+    if (!(c = malloc(offsetof(MuxerContext, priv_data) + impl->priv_data_size))) {
         fprintf(stderr, "Failed to allocate memory\n");
         return DAV1D_ERR(ENOMEM);
     }
     c->impl = impl;
-    c->data = (MuxerPriv *) &c[1];
+    c->data = (MuxerPriv *) c->priv_data;
     int have_num_pattern = 0;
     for (const char *ptr = filename ? strchr(filename, '%') : NULL;
          !have_num_pattern && ptr; ptr = strchr(ptr, '%'))
-- 
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