[xen stable-4.17] x86/extable: hide use of negative offset from array start

[patchbot@xxxxxxx]

commit 823f56e2e8e24ac8308f21b39f8c1e6a8536d946
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue May 23 14:51:19 2023 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue May 23 14:51:19 2023 +0200

    x86/extable: hide use of negative offset from array start
    
    In COVERAGE=y but DEBUG=n builds (observed by randconfig testing) gcc12
    takes issue with the subtraction of 1 from __stop___pre_ex_table[],
    considering this an out of bounds access. Not being able to know that
    the symbol actually marks the end of an array, the compiler is kind of
    right with this diagnosis. Move the subtraction into the function.
    
    Reported-by: Anthony Perard <anthony.perard@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 353b8cc56862dd808b75c6c96cd780cfee8f28bc
    master date: 2023-02-22 13:50:20 +0100
---
 xen/arch/x86/extable.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/extable.c b/xen/arch/x86/extable.c
index 4913c4a6dd..6758ba1dca 100644
--- a/xen/arch/x86/extable.c
+++ b/xen/arch/x86/extable.c
@@ -64,9 +64,10 @@ void __init sort_exception_tables(void)
 
 static unsigned long
 search_one_extable(const struct exception_table_entry *first,
-                   const struct exception_table_entry *last,
+                   const struct exception_table_entry *end,
                    unsigned long value)
 {
+    const struct exception_table_entry *last = end - 1;
     const struct exception_table_entry *mid;
     long diff;
 
@@ -91,7 +92,7 @@ search_exception_table(const struct cpu_user_regs *regs)
     unsigned long stub = this_cpu(stubs.addr);
 
     if ( region && region->ex )
-        return search_one_extable(region->ex, region->ex_end - 1, regs->rip);
+        return search_one_extable(region->ex, region->ex_end, regs->rip);
 
     if ( regs->rip >= stub + STUB_BUF_SIZE / 2 &&
          regs->rip < stub + STUB_BUF_SIZE &&
@@ -102,7 +103,7 @@ search_exception_table(const struct cpu_user_regs *regs)
 
         region = find_text_region(retptr);
         retptr = region && region->ex
-                 ? search_one_extable(region->ex, region->ex_end - 1, retptr)
+                 ? search_one_extable(region->ex, region->ex_end, retptr)
                  : 0;
         if ( retptr )
         {
@@ -198,7 +199,7 @@ search_pre_exception_table(struct cpu_user_regs *regs)
 {
     unsigned long addr = regs->rip;
     unsigned long fixup = search_one_extable(
-        __start___pre_ex_table, __stop___pre_ex_table-1, addr);
+        __start___pre_ex_table, __stop___pre_ex_table, addr);
     if ( fixup )
     {
         dprintk(XENLOG_INFO, "Pre-exception: %p -> %p\n", _p(addr), _p(fixup));
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17