loader: Fix read_targphys() to behave when read() fails

Happily passes (size_t)-1 to rom_add_blob_fixed(), which promptly dies
attempting to malloc that much.  Spotted by Coverity.

Bonus fix for ROMs larger than INT_MAX bytes: return ssize_t instead
of int.  Bug can't bite, because the only user load_aout() limits ROM
size to an int value.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/loader.c

@@ -85,11 +85,11 @@ int load_image(const char *filename, uint8_t *addr)
 }
 
 /* read()-like version */
-int read_targphys(const char *name,
+ssize_t read_targphys(const char *name,
                       int fd, target_phys_addr_t dst_addr, size_t nbytes)
 {
     uint8_t *buf;
-    size_t did;
+    ssize_t did;
 
     buf = g_malloc(nbytes);
     did = read(fd, buf, nbytes);
@@ -176,7 +176,8 @@ static void bswap_ahdr(struct exec *e)
 int load_aout(const char *filename, target_phys_addr_t addr, int max_sz,
               int bswap_needed, target_phys_addr_t target_page_size)
 {
-    int fd, size, ret;
+    int fd;
+    ssize_t size, ret;
     struct exec e;
     uint32_t magic;
 

hw/loader.h

@@ -14,7 +14,7 @@ int load_aout(const char *filename, target_phys_addr_t addr, int max_sz,
 int load_uimage(const char *filename, target_phys_addr_t *ep,
                 target_phys_addr_t *loadaddr, int *is_linux);
 
-int read_targphys(const char *name,
+ssize_t read_targphys(const char *name,
                       int fd, target_phys_addr_t dst_addr, size_t nbytes);
 void pstrcpy_targphys(const char *name,
                       target_phys_addr_t dest, int buf_size,