Changeset 58679 in vbox

Timestamp:

Nov 12, 2015 8:19:17 PM (9 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

104105

Message:

bs3kit-docs.c: Documented return registers (64-bit returns in 16-bit mode was a bit of a surprise).

File:

• trunk/src/VBox/ValidationKit/bootsectors/bs3kit/bs3kit-docs.c (modified) (1 diff)

trunk/src/VBox/ValidationKit/bootsectors/bs3kit/bs3kit-docs.c

@@ -92 +92 @@
  * protected mode to 32-bit long mode.
  *
+ * Return values are returned in the xAX register, but with the following
+ * caveats for values larger than ARCH_BITS:
+ *      - 16-bit code:
+ *          - 32-bit values are returned in AX:DX, where AX holds bits 15:0 and
+ *            DX bits 31:16.
+ *          - 64-bit values are returned in DX:CX:BX:AX, where DX holds bits
+ *            15:0, CX bits 31:16, BX bits 47:32, and AX bits 63:48.
+ *      - 32-bit code:
+ *          - 64-bit values are returned in EAX:EDX, where eax holds the least
+ *            significant bits.
+ *
  * For an in depth coverage of x86 and AMD64 calling convensions, see
  * http://homepage.ntlworld.com/jonathan.deboynepollard/FGA/function-calling-conventions.html