[patch] Patch fixes dosemu startup crash when compiled with gcc >=10

dosemu-crashWriteToCastGlobal.patch (text/plain), 2.21 KB, created by Matthew Ogilvie on 2023-06-16 05:17:54 UTC

commit b3320c3a67c0bb050b40e76831ec95a4d156890a
Author: Matthew Ogilvie <[e-mail]>
Date:   Thu Jun 15 21:55:30 2023 -0600

    mem_base: avoid undefined behavior writing to const global with casts
    
    Fix crash under gcc 10 or later.

diff --git a/src/arch/linux/mapping/mapping.c b/src/arch/linux/mapping/mapping.c
index 1d6c072..02f1dc2 100644
--- a/src/arch/linux/mapping/mapping.c
+++ b/src/arch/linux/mapping/mapping.c
@@ -47,8 +47,8 @@ static int kmem_mappings = 0;
 static struct mem_map_struct kmem_map[MAX_KMEM_MAPPINGS];
 
 static int init_done = 0;
-unsigned char * const mem_base;
-char * const lowmem_base;
+unsigned char * mem_base;
+char * lowmem_base;
 
 static struct mappingdrivers *mappingdrv[] = {
 #ifdef HAVE_SHM_OPEN
@@ -205,7 +205,7 @@ void *alias_mapping(int cap, unsigned targ, size_t mapsize, int protect, void *s
   addr = mappingdriver.alias(cap, target, mapsize, protect, source);
   update_aliasmap(target, mapsize, (cap & MAPPING_VGAEMU) ? target : source);
   if (cap & MAPPING_INIT_LOWRAM) {
-    *(unsigned char **)&mem_base = addr;
+    mem_base = addr;
   }
   return addr;
 }
@@ -416,7 +416,7 @@ void *alloc_mapping(int cap, size_t mapsize, off_t target)
 
   if (cap & MAPPING_INIT_LOWRAM) {
     Q__printf("MAPPING: LOWRAM_INIT, cap=%s, base=%p\n", cap, addr);
-    *(char **)(&lowmem_base) = addr;
+    lowmem_base = addr;
   }
   return addr;
 }
diff --git a/src/include/memory.h b/src/include/memory.h
index aa23475..d5c235c 100644
--- a/src/include/memory.h
+++ b/src/include/memory.h
@@ -209,7 +209,7 @@ void *lowmemp(const void *ptr);
    restrictions it can be non-zero. Non-zero values block vm86 but at least
    give NULL pointer protection.
 */
-extern unsigned char * const mem_base;
+extern unsigned char * mem_base;
 
 /* lowmem_base points to a shared memory image of the area 0--1MB+64K.
    It does not have any holes or mapping for video RAM etc.
@@ -221,7 +221,7 @@ extern unsigned char * const mem_base;
    It is set "const" to help GCC optimize accesses. In reality it is set only
    once, at startup
 */
-extern char * const lowmem_base;
+extern char * lowmem_base;
 
 #define UNIX_READ_BYTE(addr)		(*(Bit8u *) (addr))
 #define UNIX_WRITE_BYTE(addr, val)	(*(Bit8u *) (addr) = (val) )