From 3e0ddf70e94fdd0e3cdadbbed31bdb5f63714c16 Mon Sep 17 00:00:00 2001
From: tkchia <tkchia@users.noreply.github.com>
Date: Sun, 2 Oct 2022 15:45:25 +0800
Subject: [PATCH] Make shell script magic less prone to breakage (#643)
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The metal boot sector code was wrapped in a single-quoted
string, like so:

    MZqFpD='
    ...MZ HEADER...
    ...E_LFANEW...
    ...BIOS BOOT SECTOR...'

This might break the shell code loader if the boot sector code
contains a 0x27 (single quote) byte.  This patch wraps the
boot sector code in a here-document instead:

    MZqFpD='
    ...MZ HEADER...' <<'@'
    ...E_LFANEW...
    ...BIOS BOOT SECTOR...
    @

This is harder to break — when interpreted as a shell script,
the code can only accidentally terminate the here-document
if there is a "\n@\n" sequence inside the BIOS boot portion.
---
 ape/ape.S   | 5 ++---
 ape/ape.lds | 5 +----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/ape/ape.S b/ape/ape.S
index 7728a9fc2..72dbc8115 100644
--- a/ape/ape.S
+++ b/ape/ape.S
@@ -125,6 +125,7 @@ ape_mz:	.asciz	"MZqFpD='\n"		# Mark 'Zibo' Joseph Zbikowski
 	.org	0x24			# MZ: bytes reserved for you
 	.ascii	"JT"			# MZ: OEM identifier
 	.short	0			# MZ: OEM information
+	.ascii	"' <<'@'\n"
 	.org	0x40-4			# MZ: bytes reserved for you
 #if SupportsWindows() || SupportsMetal()
 	.long	RVA(ape_pe)		# PE: the new technology
@@ -250,7 +251,6 @@ pc:	cld
 	xor	%cx,%cx				# current cylinder
 	xor	%dh,%dh				# current head
 	mov	$v_ape_realsectors,%di		# total sectors
-	sub	$v_ape_realslacksectors,%di
 3:	call	pcread
 	dec	%di
 	jnz	3b
@@ -549,7 +549,7 @@ ape_disk:
 	the bourne executable & linkable format */
 
 #if SupportsWindows() || SupportsMetal() || SupportsXnu()
-apesh:	.ascii	"'\n#'\"\n"			# sixth edition shebang
+apesh:	.ascii	"\n@\n#'\"\n"			# sixth edition shebang
 //	Until all operating systems can be updated to support APE,
 //	we have a beautiful, yet imperfect workaround, which is to
 //	modify the binary to follow the local system's convention.
@@ -1597,7 +1597,6 @@ kernel:	movabs	$ape_stack_vaddr,%rsp
 	.ldsvar	_end
 	.ldsvar	_etext
 	.ldsvar	v_ape_realsectors
-	.ldsvar	v_ape_realslacksectors
 	.ldsvar	v_ape_highsectors
 	.ldsvar	ape_idata_ro
 	.ldsvar	ape_pad_rodata
diff --git a/ape/ape.lds b/ape/ape.lds
index 24e233b62..08c5860b0 100644
--- a/ape/ape.lds
+++ b/ape/ape.lds
@@ -565,10 +565,7 @@ SHSTUB2(ape_loader_dd_count,
 #if SupportsMetal()
 HIDDEN(v_ape_realsectors =
            MIN(0x70000 - IMAGE_BASE_REAL,
-               ROUNDUP(RVA(_edata), 4096)) / 512);
-HIDDEN(v_ape_realslacksectors =
-           v_ape_realsectors - MIN(0x70000 - IMAGE_BASE_REAL,
-                                   ROUNDUP(RVA(_edata), 512)) / 512);
+               ROUNDUP(RVA(_edata), 512)) / 512);
 HIDDEN(v_ape_realpages = v_ape_realsectors / (4096 / 512));
 HIDDEN(v_ape_highsectors =
            (ROUNDUP(RVA(_edata), 512) / 512) - v_ape_realsectors);