[Xen-devel] [PATCH v9 4/5] xen/x86: use SYMBOLS_SUBTRACT and SYMBOLS_COMPARE as required

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Use SYMBOLS_SUBTRACT and SYMBOLS_COMPARE in cases of comparisons and
subtractions of:

_start, _end, __2M_rwdata_start, __2M_rwdata_end, _stext, _etext,
__end_vpci_array, __start_vpci_array, _stextentry, _etextentry,
__trampoline_rel_start, __trampoline_rel_stop, __trampoline_seg_start,
__trampoline_seg_stop __per_cpu_start, __per_cpu_data_end

as by the C standard [1].

M3CM: Rule-18.2: Subtraction between pointers shall only be applied to
pointers that address elements of the same array

[1] 
https://wiki.sei.cmu.edu/confluence/display/c/ARR36-C.+Do+not+subtract+or+compare+two+pointers+that+do+not+refer+to+the+same+array

QAVerify: 2761
Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
CC: JBeulich@xxxxxxxx
CC: andrew.cooper3@xxxxxxxxxx
---
Changes in v9:
- use SYMBOLS_SUBTRACT and SYMBOLS_COMPARE
---
 xen/arch/x86/alternative.c  |  4 +++-
 xen/arch/x86/efi/efi-boot.h |  4 ++--
 xen/arch/x86/percpu.c       |  7 ++++---
 xen/arch/x86/setup.c        | 10 +++++++---
 xen/arch/x86/smpboot.c      |  3 ++-
 xen/drivers/vpci/vpci.c     |  2 +-
 6 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index b8c819a..56c3710 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -193,8 +193,10 @@ void init_or_livepatch apply_alternatives(struct alt_instr 
*start,
      *
      * So be careful if you want to change the scan order to any other
      * order.
+     *
+     * start and end could be pointers to different objects.
      */
-    for ( a = base = start; a < end; a++ )
+    for ( a = base = start; SYMBOLS_COMPARE(a, end) < 0; a++ )
     {
         uint8_t *orig = ALT_ORIG_PTR(a);
         uint8_t *repl = ALT_REPL_PTR(a);
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 5789d2c..12709e1 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -112,11 +112,11 @@ static void __init relocate_trampoline(unsigned long phys)
 
     /* Apply relocations to trampoline. */
     for ( trampoline_ptr = __trampoline_rel_start;
-          trampoline_ptr < __trampoline_rel_stop;
+          SYMBOLS_COMPARE(trampoline_ptr, __trampoline_rel_stop) < 0;
           ++trampoline_ptr )
         *(u32 *)(*trampoline_ptr + (long)trampoline_ptr) += phys;
     for ( trampoline_ptr = __trampoline_seg_start;
-          trampoline_ptr < __trampoline_seg_stop;
+          SYMBOLS_COMPARE(trampoline_ptr, __trampoline_seg_stop) < 0;
           ++trampoline_ptr )
         *(u16 *)(*trampoline_ptr + (long)trampoline_ptr) = phys >> 4;
 }
diff --git a/xen/arch/x86/percpu.c b/xen/arch/x86/percpu.c
index 8be4ebd..17a9c90 100644
--- a/xen/arch/x86/percpu.c
+++ b/xen/arch/x86/percpu.c
@@ -13,7 +13,8 @@ unsigned long __per_cpu_offset[NR_CPUS];
  * context of PV guests.
  */
 #define INVALID_PERCPU_AREA (0x8000000000000000L - (long)__per_cpu_start)
-#define PERCPU_ORDER get_order_from_bytes(__per_cpu_data_end - __per_cpu_start)
+#define PERCPU_ORDER get_order_from_bytes(SYMBOLS_SUBTRACT(__per_cpu_data_end, 
\
+                                                           __per_cpu_start))
 
 void __init percpu_init_areas(void)
 {
@@ -33,8 +34,8 @@ static int init_percpu_area(unsigned int cpu)
     if ( (p = alloc_xenheap_pages(PERCPU_ORDER, 0)) == NULL )
         return -ENOMEM;
 
-    memset(p, 0, __per_cpu_data_end - __per_cpu_start);
-    __per_cpu_offset[cpu] = p - __per_cpu_start;
+    memset(p, 0, SYMBOLS_SUBTRACT(__per_cpu_data_end, __per_cpu_start));
+    __per_cpu_offset[cpu] = SYMBOLS_SUBTRACT(p, __per_cpu_start);
 
     return 0;
 }
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 06eb483..11d26d7 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -600,7 +600,9 @@ static void noinline init_done(void)
     unregister_init_virtual_region();
 
     /* Zero the .init code and data. */
-    for ( va = __init_begin; va < _p(__init_end); va += PAGE_SIZE )
+    for ( va = __init_begin;
+          SYMBOLS_COMPARE(va, __init_end) < 0;
+          va += PAGE_SIZE )
         clear_page(va);
 
     /* Destroy Xen's mappings, and reuse the pages. */
@@ -972,7 +974,8 @@ void __init noreturn __start_xen(unsigned long mbi_p)
          * respective reserve_e820_ram() invocation below.
          */
         mod[mbi->mods_count].mod_start = virt_to_mfn(_stext);
-        mod[mbi->mods_count].mod_end = __2M_rwdata_end - _stext;
+        mod[mbi->mods_count].mod_end = SYMBOLS_SUBTRACT(__2M_rwdata_end,
+                                                        _stext);
     }
 
     modules_headroom = bzimage_headroom(bootstrap_map(mod), mod->mod_end);
@@ -1067,7 +1070,8 @@ void __init noreturn __start_xen(unsigned long mbi_p)
              * data until after we have switched to the relocated pagetables!
              */
             barrier();
-            move_memory(e + XEN_IMG_OFFSET, XEN_IMG_OFFSET, _end - _start, 1);
+            move_memory(e + XEN_IMG_OFFSET, XEN_IMG_OFFSET,
+                        SYMBOLS_SUBTRACT(_end, _start), 1);
 
             /* Walk initial pagetables, relocating page directory entries. */
             pl4e = __va(__pa(idle_pg_table));
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 7d1226d..0bfd4a8 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -811,7 +811,8 @@ static int setup_cpu_root_pgt(unsigned int cpu)
         const char *ptr;
 
         for ( rc = 0, ptr = _stextentry;
-              !rc && ptr < _etextentry; ptr += PAGE_SIZE )
+              !rc && SYMBOLS_COMPARE(ptr, _etextentry) < 0;
+              ptr += PAGE_SIZE )
             rc = clone_mapping(ptr, rpt);
 
         if ( rc )
diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
index 82607bd..88054da 100644
--- a/xen/drivers/vpci/vpci.c
+++ b/xen/drivers/vpci/vpci.c
@@ -33,7 +33,7 @@ struct vpci_register {
 #ifdef __XEN__
 extern vpci_register_init_t *const __start_vpci_array[];
 extern vpci_register_init_t *const __end_vpci_array[];
-#define NUM_VPCI_INIT (__end_vpci_array - __start_vpci_array)
+#define NUM_VPCI_INIT (SYMBOLS_SUBTRACT(__end_vpci_array, __start_vpci_array))
 
 void vpci_remove_device(struct pci_dev *pdev)
 {
-- 
1.9.1


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