[romprefix] Update ROM checksum even if PMM allocation fails

There are code paths other than PMM allocation that can result in our
changing the ROM checksum.  For example, we attempt to update our
product string to incorporate the PCI bus:dev.fn number.  In a system
that does not support PMM, we could therefore end up with an incorrect
checksum.

Fix by attempting to update the checksum unconditionally.

diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index d248916d4d76fe469f443d2eb8c4233e45864c6d..2664e340ab597007b8ec374469332e193ba9d83b 100644 (file)
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -345,20 +345,22 @@ got_pmm: /* PMM allocation succeeded */
        shll    $9, %ecx
        addr32 rep movsb        /* PMM presence implies flat real mode */
        movl    %edi, decompress_to
-       /* Shrink ROM and update checksum */
+       /* Shrink ROM */
+       movb    $_prefix_memsz_sect, romheader_size
+pmm_fail:
+       /* Restore upper register halves */
+       popal
+no_pmm:
+
+       /* Update checksum */
        xorw    %bx, %bx
        xorw    %si, %si
-       movw    $_prefix_memsz_sect, %cx
-       movb    %cl, romheader_size
+       movzbw  romheader_size, %cx
        shlw    $9, %cx
 1:     lodsb
        addb    %al, %bl
        loop    1b
        subb    %bl, checksum
-pmm_fail:
-       /* Restore upper register halves */
-       popal
-no_pmm:
 
        /* Copy self to option ROM space.  Required for PCI3.0, which
         * loads us to a temporary location in low memory.  Will be a