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Bug 3875 - SDL_NewAudioStream() fails if calloc(0, xx) returns NULL
Summary: SDL_NewAudioStream() fails if calloc(0, xx) returns NULL
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: audio (show other bugs)
Version: HG 2.0
Hardware: All All
: P2 normal
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2017-10-12 08:33 UTC by Ozkan Sezer
Modified: 2017-10-12 15:13 UTC (History)
0 users

See Also:

Attachments
SDL_malloc patch (718 bytes, patch)
2017-10-12 11:32 UTC, Ozkan Sezer 		Details | Diff
View All Add an attachment (proposed patch, testcase, etc.)

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Description Ozkan Sezer 2017-10-12 08:33:52 UTC 
Since recent changes, I have been getting out of memory errors upon
trying to initialize audio on OS/2.  With the Dart implementation I
am using, I am hitting (device->spec.samples != obtained->samples)
in SDL_audio.c:open_audio_device() so it sets build_stream = SDL_TRUE
and calls SDL_NewAudioStream().  SDL_audiocvt.c:ResamplerPadding()
returns 0 because inrate == outrate, that results in SDL_calloc()
returning NULL for retval->resampler_padding_samples which results
in the failure return from SDL_NewAudioStream().

It is legal for malloc() or calloc() to return NULL for a 0 size arg,
and obviously Watcom runtime does exactly that.  I don't exactly know
which particular changeset opened the way for this failure.  I made a
hack like below and it works for me (TM):


--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -1260,6 +1260,7 @@ SDL_NewAudioStream(const SDL_AudioFormat
     const int packetlen = 4096;  /* !!! FIXME: good enough for now. */
     Uint8 pre_resample_channels;
     SDL_AudioStream *retval;
+    int nelem; /* for calloc() */
 
     retval = (SDL_AudioStream *) SDL_calloc(1, sizeof (SDL_AudioStream));
     if (!retval) {
@@ -1285,7 +1286,11 @@ SDL_NewAudioStream(const SDL_AudioFormat
     retval->packetlen = packetlen;
     retval->rate_incr = ((double) dst_rate) / ((double) src_rate);
     retval->resampler_padding_samples = ResamplerPadding(retval->src_rate, retval->dst_rate) * pre_resample_channels;
-    retval->resampler_padding = (float *) SDL_calloc(retval->resampler_padding_samples, sizeof (float));
+    nelem = retval->resampler_padding_samples;
+    if (nelem == 0) {
+        nelem = 1;
+    }
+    retval->resampler_padding = (float *) SDL_calloc(nelem, sizeof (float));
 
     if (retval->resampler_padding == NULL) {
         SDL_FreeAudioStream(retval);
@@ -1313,7 +1318,7 @@ SDL_NewAudioStream(const SDL_AudioFormat
 #endif
 
         if (!retval->resampler_func) {
-            retval->resampler_state = SDL_calloc(retval->resampler_padding_samples, sizeof (float));
+            retval->resampler_state = SDL_calloc(nelem, sizeof (float));
             if (!retval->resampler_state) {
                 SDL_FreeAudioStream(retval);
                 SDL_OutOfMemory();


Of course there might be other ways of working around this, which
I leave to you guys.
Comment 1 Ozkan Sezer 2017-10-12 11:32:15 UTC 
Created attachment 2979 [details]
SDL_malloc patch

An alternative (possibly better?) soulution would be making sure that
SDL_malloc(0) or SDL_calloc(0, x) doesn't return NULL, like below:
(also attached).

# HG changeset patch
# User Ozkan Sezer <sezero@users.sourceforge.net>
# Date 1507807685 -10800
#      Thu Oct 12 14:28:05 2017 +0300
# Node ID bee06d420e14cadddfee53da5a8ff40508e9dfd5
# Parent  0f2de8f6c959f98264ac99869038a7999f96f5f0
make sure that SDL_malloc(0) or SDL_calloc(0,x) doesn't return NULL.

diff --git a/src/stdlib/SDL_malloc.c b/src/stdlib/SDL_malloc.c
--- a/src/stdlib/SDL_malloc.c
+++ b/src/stdlib/SDL_malloc.c
@@ -33,11 +33,17 @@
 
 void *SDL_malloc(size_t size)
 {
+    if (!size) {
+        return malloc(1);
+    }
     return malloc(size);
 }
 
 void *SDL_calloc(size_t nmemb, size_t size)
 {
+    if (!size || !nmemb) {
+        return calloc(1,1);
+    }
     return calloc(nmemb, size);
 }
Comment 2 Sam Lantinga 2017-10-12 15:13:29 UTC 
I like the idea of making SDL_malloc() and friends have consistent zero size alloc behavior.
https://hg.libsdl.org/SDL/rev/22fe56a64c6f

Thanks!