From: Taylor R Campbell <campbell@mumble.net>
Date: Fri, 25 Jan 2019 04:31:15 +0000 (+0000)
Subject: Fix comment about ADRP to reflect reality.
X-Git-Tag: mit-scheme-pucked-10.1.20~11^2~66^2~17
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=8b2e18eb0902bbaa6397bdca6bc83ec794b5cd4f;p=mit-scheme.git

Fix comment about ADRP to reflect reality.
---

diff --git a/src/microcode/cmpintmd/aarch64.c b/src/microcode/cmpintmd/aarch64.c
index 54aa33e5c..af2c6f3b5 100644
--- a/src/microcode/cmpintmd/aarch64.c
+++ b/src/microcode/cmpintmd/aarch64.c
@@ -270,9 +270,9 @@ write_uuo_insns (insn_t * target, insn_t * iaddr, int pcrel)
 	}
       else
 	{
-	  /* ADRP takes 21-bit signed number of 4096-byte pages, and
-	     adds that many 4096-byte pages to the PC.  We then need to
-	     add the offset within a page of the target.  */
+	  /* ADRP computes PC - (PC mod 2^12) + 2^12*offset.  We know
+	     target - PC, and we want target.  First we add the page
+	     offset; then we add target's location in its page.  */
 	  uintptr_t from_pg = (((uintptr_t) from_pc) >> 12);
 	  uintptr_t to_pg = (((uintptr_t) to_pc) >> 12);
 	  ptrdiff_t pgoff = (((intptr_t) to_pg) - ((intptr_t) from_pg));