[PATCH 0/2] Realloc fixes version 2

[PATCH 0/2] Realloc fixes version 2

[Keith Packard]

Here's an updated pair which fixes a bug where realloc was reading off
the source, and then addresses a TODO item to shrink the buffer when
the new size is much smaller.

[PATCH 1/2] libm/stdlib: don't read past source in nano_realloc

[Keith Packard]

Save the computed block size and use it to avoid reading past
the end of the source block.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 newlib/libc/stdlib/nano-mallocr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
index 04465eb9e..5028431ec 100644
--- a/newlib/libc/stdlib/nano-mallocr.c
+++ b/newlib/libc/stdlib/nano-mallocr.c
@@ -466,6 +466,7 @@ void * nano_realloc(RARG void * ptr, malloc_size_t size)
 {
     void * mem;
     chunk * p_to_realloc;
+    malloc_size_t old_size;
 
     if (ptr == NULL) return nano_malloc(RCALL size);
 
@@ -477,13 +478,14 @@ void * nano_realloc(RARG void * ptr, malloc_size_t size)
 
     /* TODO: There is chance to shrink the chunk if newly requested
      * size is much small */
-    if (nano_malloc_usable_size(RCALL ptr) >= size)
+    old_size = nano_malloc_usable_size(RCALL ptr);
+    if (old_size >= size)
       return ptr;
 
     mem = nano_malloc(RCALL size);
     if (mem != NULL)
     {
-        memcpy(mem, ptr, size);
+        memcpy(mem, ptr, old_size);
         nano_free(RCALL ptr);
     }
     return mem;
-- 
2.28.0

[PATCH 2/2] libm/stdlib: Realloc when shrinking by 2* or more

[Keith Packard]

This reduces memory usage when reallocating objects much smaller.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 newlib/libc/stdlib/nano-mallocr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
index 5028431ec..d178c34ab 100644
--- a/newlib/libc/stdlib/nano-mallocr.c
+++ b/newlib/libc/stdlib/nano-mallocr.c
@@ -476,15 +476,15 @@ void * nano_realloc(RARG void * ptr, malloc_size_t size)
         return NULL;
     }
 
-    /* TODO: There is chance to shrink the chunk if newly requested
-     * size is much small */
     old_size = nano_malloc_usable_size(RCALL ptr);
-    if (old_size >= size)
+    if (size <= old_size && (old_size >> 1) < size)
       return ptr;
 
     mem = nano_malloc(RCALL size);
     if (mem != NULL)
     {
+	if (old_size > size)
+	    old_size = size;
         memcpy(mem, ptr, old_size);
         nano_free(RCALL ptr);
     }
-- 
2.28.0

Re: [PATCH 0/2] Realloc fixes version 2

[Corinna Vinschen]

On Aug 13 17:19, Keith Packard via Newlib wrote:
> Here's an updated pair which fixes a bug where realloc was reading off
> the source, and then addresses a TODO item to shrink the buffer when
> the new size is much smaller.
> 

Pushed.


Thanks,
Corinna