From fd2ef8ef5a054d9f26b6b36ea56a5414c7683e39 Mon Sep 17 00:00:00 2001
From: Maxim Sobolev <sobomax@FreeBSD.org>
Date: Wed, 25 Nov 2020 23:19:01 +0000
Subject: [PATCH] Unobfuscate "KERNLOAD" parameter on amd64. This change
 lines-up amd64 with the i386 and the rest of supported architectures by
 defining KERNLOAD in the vmparam.h and getting rid of magic constant in the
 linker script, which albeit documented via comment but isn't programmatically
 accessible at a compile time.

Use KERNLOAD to eliminate another (matching) magic constant 100 lines down
inside unremarkable TU "copy.c" 3 levels deep in the EFI loader tree.

Reviewed by:	markj
Approved by:	markj
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D27355
---
 stand/efi/loader/copy.c     | 8 +++-----
 sys/amd64/amd64/genassym.c  | 1 +
 sys/amd64/amd64/locore.S    | 3 ++-
 sys/amd64/include/vmparam.h | 8 ++++++++
 sys/conf/ldscript.amd64     | 2 +-
 5 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/stand/efi/loader/copy.c b/stand/efi/loader/copy.c
index 1185c94740d..17a4c57f865 100644
--- a/stand/efi/loader/copy.c
+++ b/stand/efi/loader/copy.c
@@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
 #if defined(__i386__) || defined(__amd64__)
 #include <machine/cpufunc.h>
 #include <machine/specialreg.h>
+#include <machine/vmparam.h>
 
 /*
  * The code is excerpted from sys/x86/x86/identcpu.c: identify_cpu(),
@@ -89,8 +90,6 @@ running_on_hyperv(void)
 	return (1);
 }
 
-#define KERNEL_PHYSICAL_BASE (2*1024*1024)
-
 static void
 efi_verify_staging_size(unsigned long *nr_pages)
 {
@@ -134,12 +133,11 @@ efi_verify_staging_size(unsigned long *nr_pages)
 		start = p->PhysicalStart;
 		end = start + p->NumberOfPages * EFI_PAGE_SIZE;
 
-		if (KERNEL_PHYSICAL_BASE < start ||
-		    KERNEL_PHYSICAL_BASE >= end)
+		if (KERNLOAD < start || KERNLOAD >= end)
 			continue;
 
 		available_pages = p->NumberOfPages -
-			((KERNEL_PHYSICAL_BASE - start) >> EFI_PAGE_SHIFT);
+			((KERNLOAD - start) >> EFI_PAGE_SHIFT);
 		break;
 	}
 
diff --git a/sys/amd64/amd64/genassym.c b/sys/amd64/amd64/genassym.c
index f643eeeb07b..f89c53e7550 100644
--- a/sys/amd64/amd64/genassym.c
+++ b/sys/amd64/amd64/genassym.c
@@ -115,6 +115,7 @@ ASSYM(val_KPML4I, KPML4I);
 ASSYM(val_PML4PML4I, PML4PML4I);
 ASSYM(VM_MAXUSER_ADDRESS, VM_MAXUSER_ADDRESS);
 ASSYM(KERNBASE, KERNBASE);
+ASSYM(KERNLOAD, KERNLOAD);
 ASSYM(DMAP_MIN_ADDRESS, DMAP_MIN_ADDRESS);
 ASSYM(DMAP_MAX_ADDRESS, DMAP_MAX_ADDRESS);
 
diff --git a/sys/amd64/amd64/locore.S b/sys/amd64/amd64/locore.S
index a9a7b5f3972..3addc3fb10c 100644
--- a/sys/amd64/amd64/locore.S
+++ b/sys/amd64/amd64/locore.S
@@ -36,8 +36,9 @@
 /*
  * Compiled KERNBASE location
  */
-	.globl	kernbase, loc_PTmap, loc_PDmap, loc_PDPmap, dmapbase, dmapend
+	.globl	kernbase, kernload, loc_PTmap, loc_PDmap, loc_PDPmap, dmapbase, dmapend
 	.set	kernbase,KERNBASE
+	.set    kernload,KERNLOAD
 	.set	dmapbase,DMAP_MIN_ADDRESS
 	.set	dmapend,DMAP_MAX_ADDRESS
 
diff --git a/sys/amd64/include/vmparam.h b/sys/amd64/include/vmparam.h
index 5d3010e2e25..c7ffb218dd4 100644
--- a/sys/amd64/include/vmparam.h
+++ b/sys/amd64/include/vmparam.h
@@ -148,6 +148,14 @@
 #define	PA_LOCK_COUNT	256
 #endif
 
+/*
+ * Kernel physical load address. Needs to be aligned at 2MB superpage
+ * boundary.
+ */
+#ifndef KERNLOAD
+#define	KERNLOAD	0x200000
+#endif
+
 /*
  * Virtual addresses of things.  Derived from the page directory and
  * page table indexes from pmap.h for precision.
diff --git a/sys/conf/ldscript.amd64 b/sys/conf/ldscript.amd64
index d62b531454e..c11ffb6ea49 100644
--- a/sys/conf/ldscript.amd64
+++ b/sys/conf/ldscript.amd64
@@ -5,8 +5,8 @@ ENTRY(btext)
 SEARCH_DIR("/usr/lib");
 SECTIONS
 {
+  kernphys = kernload;
   /* Read-only sections, merged into text segment: */
-  kernphys = 0x200000; /* 2MB superpage size */
   . = kernbase + kernphys + SIZEOF_HEADERS;
   /*
    * Use the AT keyword in order to set the right LMA that contains