File dosemu-LTO-fix.patch of Package dosemu-1.4.0.1.r2065-182.1

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File dosemu-LTO-fix.patch of Package dosemu-1.4.0.1.r2065-182.1

From: Jiri Slaby <jslaby@suse.cz>
Subject: remove undefined behaviour/fix LTO build
References: bnc#1160098

The code defines two const pointers:
  unsigned char * const mem_base;
  char * const lowmem_base;

They are set during setup.

But the C standard clearly states:
  If an attempt is made to modify an object defined with a
  const-qualified type through use of an lvalue with non-const-qualified
  type, the behavior is undefined.
  
This pretty nicely breaks when using modern gcc with LTO enabled. Gcc
thinks the point is always NULL, as was initialized.

This was fixed in dosemu2 by:
https://github.com/stsp/dosemu2/commit/d36496646b31891ce952f3e9b63946a2ff2371b3
https://github.com/stsp/dosemu2/commit/bb4437f93912d4d47961d2cbb0f13c737f8295c2
---
 src/arch/linux/mapping/mapping.c |    6 +++---
 src/base/init/init.c             |    2 +-
 src/include/memory.h             |    9 +++++----
 3 files changed, 9 insertions(+), 8 deletions(-)

--- a/src/arch/linux/mapping/mapping.c
+++ b/src/arch/linux/mapping/mapping.c
@@ -57,8 +57,8 @@ 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;
 #ifndef HAVE_MREMAP_FIXED
 int have_mremap_fixed = 1;
 #endif
@@ -427,7 +427,7 @@ void *alloc_mapping(int cap, size_t maps
   if (cap & MAPPING_INIT_LOWRAM) {
     PRIV_SAVE_AREA
     Q__printf("MAPPING: LOWRAM_INIT, cap=%s, base=%p\n", cap, addr);
-    *(char **)(&lowmem_base) = addr;
+    lowmem_base = addr;
     /* we may need root to mmap address 0 */
     enter_priv_on();
     addr = alias_mapping(MAPPING_INIT_LOWRAM, 0,
--- a/src/base/init/init.c
+++ b/src/base/init/init.c
@@ -310,7 +310,7 @@ void low_mem_init(void)
 	 "WARN: as root, or by changing the vm.mmap_min_addr setting in\n"
 	 "WARN: /etc/sysctl.conf or a file in /etc/sysctl.d/ to 0.\n",
 	    result);
-    *(unsigned char **)&mem_base = result;
+    mem_base = result;
 #endif
   }
 
--- a/src/include/memory.h
+++ b/src/include/memory.h
@@ -233,7 +233,7 @@ 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.
@@ -242,10 +242,11 @@ extern unsigned char * const mem_base;
    simx86, NULL page protection, and removal of the VGA protected memory
    access hack.
 
-   It is set "const" to help GCC optimize accesses. In reality it is set only
-   once, at startup
+   It is not set "const" as it is set once, at startup. Making it const
+   would violate the C standard and would cause crashes and/or weird
+   behaviour.
 */
-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) )

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File dosemu-LTO-fix.patch of Package dosemu-1.4.0.1.r2065-182.1

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