[PATCH 0/2] MR868: ntdll, libwine: Avoid comparing the result of pointer arithmetic to zero.

[Zebediah Figura (＠zfigura)]

It's not exactly clear to me why gcc warns about this (and it's hard to find
reference for this specific flavor of -Waddress), but my understanding is that
arithmetic on well-defined pointers will never yield NULL. Of course, we are not
dealing with well-defined pointers here, but fortunately gcc does not complain
if we cast to intptr_t first.

[PATCH 1/2] ntdll: Avoid comparing the result of pointer arithmetic to zero.

[Zebediah Figura]

From: Zebediah Figura

gcc warns about this:

../wine/dlls/ntdll/unix/virtual.c: In function ‘mmap_add_reserved_area’:
../wine/dlls/ntdll/unix/virtual.c:241:9: error: the comparison will always evaluate as ‘true’ for the pointer operand in ‘(char *)addr + (sizetype)size’ must not be NULL [-Werror=address]
  241 |     if (!((char *)addr + size)) size--;  /* avoid wrap-around */
      |         ^
---
 dlls/ntdll/unix/virtual.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dlls/ntdll/unix/virtual.c b/dlls/ntdll/unix/virtual.c
index 96a5e095d16..e0aa410373e 100644
--- a/dlls/ntdll/unix/virtual.c
+++ b/dlls/ntdll/unix/virtual.c
@@ -238,7 +238,7 @@ static void mmap_add_reserved_area( void *addr, SIZE_T size )
     struct reserved_area *area;
     struct list *ptr;

-    if (!((char *)addr + size)) size--;  /* avoid wrap-around */
+    if (!((intptr_t)addr + size)) size--;  /* avoid wrap-around */

LIST_FOR_EACH( ptr, &reserved_areas )
     {
@@ -287,7 +287,7 @@ static void mmap_remove_reserved_area( void *addr, SIZE_T size )
     struct reserved_area *area;
     struct list *ptr;

-    if (!((char *)addr + size)) size--;  /* avoid wrap-around */
+    if (!((intptr_t)addr + size)) size--;  /* avoid wrap-around */

ptr = list_head( &reserved_areas );
     /* find the first area covering address */

[PATCH 2/2] libwine: Avoid comparing the result of pointer arithmetic to zero.

[Zebediah Figura]

From: Zebediah Figura

gcc warns about this:

../wine/libs/wine/mmap.c: In function ‘wine_mmap_add_reserved_area_obsolete’:
../wine/libs/wine/mmap.c:504:9: error: the comparison will always evaluate as ‘true’ for the pointer operand in ‘(char *)addr + (sizetype)size’ must not be NULL [-Werror=address]
  504 |     if (!((char *)addr + size)) size--;  /* avoid wrap-around */
      |         ^
---
 libs/wine/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libs/wine/mmap.c b/libs/wine/mmap.c
index ad51153d039..1f8ae3c7720 100644
--- a/libs/wine/mmap.c
+++ b/libs/wine/mmap.c
@@ -501,7 +501,7 @@ void wine_mmap_add_reserved_area_obsolete( void *addr, size_t size )
     struct reserved_area *area;
     struct list *ptr;

-    if (!((char *)addr + size)) size--;  /* avoid wrap-around */
+    if (!((intptr_t)addr + size)) size--;  /* avoid wrap-around */

LIST_FOR_EACH( ptr, &reserved_areas )
     {
@@ -560,7 +560,7 @@ void wine_mmap_remove_reserved_area_obsolete( void *addr, size_t size, int unmap
     struct reserved_area *area;
     struct list *ptr;

-    if (!((char *)addr + size)) size--;  /* avoid wrap-around */
+    if (!((intptr_t)addr + size)) size--;  /* avoid wrap-around */

ptr = list_head( &reserved_areas );
     /* find the first area covering address */