rombios: Work around GCC issue 99578

GCC 12 objects to pointers derived from a constant:

  util.c: In function 'find_rsdp':
  util.c:429:16: error: array subscript 0 is outside array bounds of 'uint16_t[0]' {aka 'short unsigned int[]'} [-Werror=array-bounds]
    429 |     ebda_seg = *(uint16_t *)ADDR_FROM_SEG_OFF(0x40, 0xe);
  cc1: all warnings being treated as errors

This is a GCC bug, but work around it rather than turning array-bounds
checking off generally.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit e35138a2ffbe1fe71edaaaaae71063dc545a8416)

diff --git a/tools/firmware/rombios/32bit/util.c b/tools/firmware/rombios/32bit/util.c
index 6c1c4805144bf520abe6545f70bb0720a709102b..a47e000a2629be3b1d417c19062d18116139f00f 100644 (file)
--- a/tools/firmware/rombios/32bit/util.c
+++ b/tools/firmware/rombios/32bit/util.c
@@ -424,10 +424,10 @@ static struct acpi_20_rsdp *__find_rsdp(const void *start, unsigned int len)
 struct acpi_20_rsdp *find_rsdp(void)
 {
     struct acpi_20_rsdp *rsdp;
-    uint16_t ebda_seg;
+    uint16_t *volatile /* GCC issue 99578 */ ebda_seg =
+        ADDR_FROM_SEG_OFF(0x40, 0xe);
 
-    ebda_seg = *(uint16_t *)ADDR_FROM_SEG_OFF(0x40, 0xe);
-    rsdp = __find_rsdp((void *)(ebda_seg << 16), 1024);
+    rsdp = __find_rsdp((void *)(*ebda_seg << 16), 1024);
     if (!rsdp)
         rsdp = __find_rsdp((void *)0xE0000, 0x20000);