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Message-ID: <6e1db6ad9e8ebd3d2de116b004ed09bb9de30075.1761919305.git.alx@kernel.org>
Date: Fri, 31 Oct 2025 15:01:58 +0100
From: Alejandro Colomar <alx@...nel.org>
To: musl@...ts.openwall.com
Cc: Alejandro Colomar <alx@...nel.org>,
"A. Wilcox" <AWilcox@...cox-tech.com>, Lénárd Szolnoki <cpp@...ardszolnoki.com>,
Thorsten Glaser <tg@...bsd.de>, Collin Funk <collin.funk1@...il.com>
Subject: [RFC] add realloci() and reallocarrayi()
They are realloc(3) variants that work in-place. They change the size
of a block of memory, without affecting the lifetime of the object.
It requires a non-null pointer, unlike realloc(3), as it can't create
a new object (it doesn't return a pointer).
Cc: "A. Wilcox" <AWilcox@...cox-tech.com>
Cc: Lénárd Szolnoki <cpp@...ardszolnoki.com>
Cc: Thorsten Glaser <tg@...bsd.de>
Cc: Collin Funk <collin.funk1@...il.com>
Signed-off-by: Alejandro Colomar <alx@...nel.org>
---
Hi,
I have not tested this patch (not even tried building yet). It's just
an initial draft, requesting comments about the overall idea.
So far, I've only implemented this in the mallocng implementation, as
the oldmalloc implementation was too weird for me to fully understand.
Do we need an old implementation too?
Have a lovely day!
Alex
include/stdlib.h | 2 ++
ldso/dynlink.c | 1 +
src/aio/aio.c | 1 +
src/exit/atexit.c | 1 +
src/ldso/dlerror.c | 1 +
src/locale/dcngettext.c | 1 +
src/locale/duplocale.c | 1 +
src/locale/freelocale.c | 1 +
src/locale/locale_map.c | 1 +
src/locale/newlocale.c | 1 +
src/malloc/mallocng/glue.h | 1 +
src/malloc/mallocng/realloc.c | 8 +-------
src/malloc/mallocng/realloci.c | 26 ++++++++++++++++++++++++++
src/malloc/reallocarrayi.c | 13 +++++++++++++
src/malloc/realloci.c | 7 +++++++
src/process/fdop.h | 1 +
src/thread/pthread_atfork.c | 1 +
src/thread/sem_open.c | 1 +
src/time/__tz.c | 1 +
19 files changed, 63 insertions(+), 7 deletions(-)
create mode 100644 src/malloc/mallocng/realloci.c
create mode 100644 src/malloc/reallocarrayi.c
create mode 100644 src/malloc/realloci.c
diff --git a/include/stdlib.h b/include/stdlib.h
index 475190bf..577b7172 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -148,6 +148,8 @@ int clearenv(void);
#define WCOREDUMP(s) ((s) & 0x80)
#define WIFCONTINUED(s) ((s) == 0xffff)
void *reallocarray (void *, size_t, size_t);
+int realloci (void *, size_t);
+int reallocarrayi (void *, size_t);
void qsort_r (void *, size_t, size_t, int (*)(const void *, const void *, void *), void *);
#endif
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 715948f4..a882c5c1 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -35,6 +35,7 @@ static size_t ldso_page_size;
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc __libc_realloc
+#define realloci __libc_realloci
#define free __libc_free
static void error_impl(const char *, ...);
diff --git a/src/aio/aio.c b/src/aio/aio.c
index d7e063bf..4702d0ae 100644
--- a/src/aio/aio.c
+++ b/src/aio/aio.c
@@ -14,6 +14,7 @@
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc __libc_realloc
+#define realloci __libc_realloci
#define free __libc_free
/* The following is a threads-based implementation of AIO with minimal
diff --git a/src/exit/atexit.c b/src/exit/atexit.c
index 92c91c9d..006551e7 100644
--- a/src/exit/atexit.c
+++ b/src/exit/atexit.c
@@ -7,6 +7,7 @@
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc undef
+#define realloci undef
#define free undef
/* Ensure that at least 32 atexit handlers can be registered without malloc */
diff --git a/src/ldso/dlerror.c b/src/ldso/dlerror.c
index dae0f3a9..7cf55f17 100644
--- a/src/ldso/dlerror.c
+++ b/src/ldso/dlerror.c
@@ -8,6 +8,7 @@
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc __libc_realloc
+#define realloci __libc_realloci
#define free __libc_free
char *dlerror()
diff --git a/src/locale/dcngettext.c b/src/locale/dcngettext.c
index 0b53286d..782bb942 100644
--- a/src/locale/dcngettext.c
+++ b/src/locale/dcngettext.c
@@ -15,6 +15,7 @@
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc undef
+#define realloci undef
#define free undef
struct binding {
diff --git a/src/locale/duplocale.c b/src/locale/duplocale.c
index 5ce33ae6..093b3358 100644
--- a/src/locale/duplocale.c
+++ b/src/locale/duplocale.c
@@ -6,6 +6,7 @@
#define malloc __libc_malloc
#define calloc undef
#define realloc undef
+#define realloci undef
#define free undef
locale_t __duplocale(locale_t old)
diff --git a/src/locale/freelocale.c b/src/locale/freelocale.c
index 385d1206..f73a0ada 100644
--- a/src/locale/freelocale.c
+++ b/src/locale/freelocale.c
@@ -4,6 +4,7 @@
#define malloc undef
#define calloc undef
#define realloc undef
+#define realloci undef
#define free __libc_free
void freelocale(locale_t l)
diff --git a/src/locale/locale_map.c b/src/locale/locale_map.c
index da61f7fc..de49f1b7 100644
--- a/src/locale/locale_map.c
+++ b/src/locale/locale_map.c
@@ -10,6 +10,7 @@
#define malloc __libc_malloc
#define calloc undef
#define realloc undef
+#define realloci undef
#define free undef
const char *__lctrans_impl(const char *msg, const struct __locale_map *lm)
diff --git a/src/locale/newlocale.c b/src/locale/newlocale.c
index 9ac3cd38..883c9512 100644
--- a/src/locale/newlocale.c
+++ b/src/locale/newlocale.c
@@ -7,6 +7,7 @@
#define malloc __libc_malloc
#define calloc undef
#define realloc undef
+#define realloci undef
#define free undef
static int default_locale_init_done;
diff --git a/src/malloc/mallocng/glue.h b/src/malloc/mallocng/glue.h
index 77f4c812..37e6b6cd 100644
--- a/src/malloc/mallocng/glue.h
+++ b/src/malloc/mallocng/glue.h
@@ -22,6 +22,7 @@
#define malloc __libc_malloc_impl
#define realloc __libc_realloc
+#define realloci __libc_realloci
#define free __libc_free
#define USE_MADV_FREE 0
diff --git a/src/malloc/mallocng/realloc.c b/src/malloc/mallocng/realloc.c
index 18769f42..92f8eea5 100644
--- a/src/malloc/mallocng/realloc.c
+++ b/src/malloc/mallocng/realloc.c
@@ -15,15 +15,9 @@ void *realloc(void *p, size_t n)
unsigned char *start = g->mem->storage + stride*idx;
unsigned char *end = start + stride - IB;
size_t old_size = get_nominal_size(p, end);
- size_t avail_size = end-(unsigned char *)p;
void *new;
- // only resize in-place if size class matches
- if (n <= avail_size && n<MMAP_THRESHOLD
- && size_to_class(n)+1 >= g->sizeclass) {
- set_size(p, end, n);
- return p;
- }
+ if (realloci(p, n) == 0) return p;
// use mremap if old and new size are both mmap-worthy
if (g->sizeclass>=48 && n>=MMAP_THRESHOLD) {
diff --git a/src/malloc/mallocng/realloci.c b/src/malloc/mallocng/realloci.c
new file mode 100644
index 00000000..590f1b18
--- /dev/null
+++ b/src/malloc/mallocng/realloci.c
@@ -0,0 +1,26 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <string.h>
+#include "meta.h"
+
+int realloci(void *p, size_t n)
+{
+ if (size_overflows(n)) return -1;
+
+ struct meta *g = get_meta(p);
+ int idx = get_slot_index(p);
+ size_t stride = get_stride(g);
+ unsigned char *start = g->mem->storage + stride*idx;
+ unsigned char *end = start + stride - IB;
+ size_t avail_size = end-(unsigned char *)p;
+
+ // only resize in-place if size class matches
+ if (n <= avail_size && n<MMAP_THRESHOLD
+ && size_to_class(n)+1 >= g->sizeclass) {
+ set_size(p, end, n);
+ return 0;
+ }
+
+ return -1;
+}
diff --git a/src/malloc/reallocarrayi.c b/src/malloc/reallocarrayi.c
new file mode 100644
index 00000000..8afaa761
--- /dev/null
+++ b/src/malloc/reallocarrayi.c
@@ -0,0 +1,13 @@
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdlib.h>
+
+int reallocarrayi(void *ptr, size_t m, size_t n)
+{
+ if (n && m > -1 / n) {
+ errno = ENOMEM;
+ return 0;
+ }
+
+ return realloci(ptr, m * n);
+}
diff --git a/src/malloc/realloci.c b/src/malloc/realloci.c
new file mode 100644
index 00000000..f1ba8138
--- /dev/null
+++ b/src/malloc/realloci.c
@@ -0,0 +1,7 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+
+int realloci(void *p, size_t n)
+{
+ return __libc_realloci(p, n);
+}
diff --git a/src/process/fdop.h b/src/process/fdop.h
index 7cf733b2..a25914d9 100644
--- a/src/process/fdop.h
+++ b/src/process/fdop.h
@@ -14,4 +14,5 @@ struct fdop {
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc undef
+#define realloci undef
#define free __libc_free
diff --git a/src/thread/pthread_atfork.c b/src/thread/pthread_atfork.c
index 26d32543..c5951f81 100644
--- a/src/thread/pthread_atfork.c
+++ b/src/thread/pthread_atfork.c
@@ -6,6 +6,7 @@
#define malloc __libc_malloc
#define calloc undef
#define realloc undef
+#define realloci undef
#define free undef
static struct atfork_funcs {
diff --git a/src/thread/sem_open.c b/src/thread/sem_open.c
index 0ad29de9..a74ae00d 100644
--- a/src/thread/sem_open.c
+++ b/src/thread/sem_open.c
@@ -17,6 +17,7 @@
#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc undef
+#define realloci undef
#define free undef
static struct {
diff --git a/src/time/__tz.c b/src/time/__tz.c
index 54ed4cf6..76798fd0 100644
--- a/src/time/__tz.c
+++ b/src/time/__tz.c
@@ -12,6 +12,7 @@
#define malloc __libc_malloc
#define calloc undef
#define realloc undef
+#define realloci undef
#define free undef
long __timezone = 0;
Range-diff:
-: -------- > 1: 6e1db6ad add realloci() and reallocarrayi()
--
2.51.0
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