From 18ccfeb9191d723644d68ab125ad2cea696782ff Mon Sep 17 00:00:00 2001
From: Florian Lemaitre <lemaitre@users.noreply.github.com>
Date: Sat, 18 Sep 2021 01:49:10 +0200
Subject: [PATCH] Embed APE loader inside APE (#267)

The `ape-no-modify-self.o` bootloader now has an mmap-based
payload that helps read-only APE binaries be load faster since it
doesn't need to copy any files.
---
 ape/ape.S   | 26 +++++++++++++++++++++++++-
 ape/ape.lds | 12 ++++++++++++
 ape/ape.mk  |  4 ++--
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/ape/ape.S b/ape/ape.S
index 42a088287..85a468837 100644
--- a/ape/ape.S
+++ b/ape/ape.S
@@ -540,11 +540,30 @@ apesh:	.ascii	"'\n#'\"\n"			# sixth edition shebang
 //	modify the binary to follow the local system's convention.
 //	There isn't a one-size-fits-all approach for this, thus we
 //	present two choices.
+	.ascii	"o=\"$(command -v \"$0\")\"\n"
+//	Try to use a system-wide APE loader.
+	.ascii	"type ape-loader >/dev/null 2>&1 && "
+	.ascii	"exec ape-loader \"$o\" \"$@\"\n"
+#ifdef APE_LOADER
+//	There is no system-wide APE loader, but there is one
+//	embedded inside the APE. So if the system is not MacOs,
+//	extract the loader into a temp folder, and use it to
+//	load the APE without modifying it.
+	.ascii	"if [ ! -d /Applications ]; then\n"
+	.ascii	  "t=\"${TMPDIR:-/tmp}/ape-loader\"\n"
+	.ascii	  "[ -x \"$t\" ] || {\ndd if=\"$o\" of=\"$t\" skip=\""
+	.shstub	    ape_loader_dd_skip,2
+	.ascii	    "\" count=\""
+	.shstub	    ape_loader_dd_count,2
+	.ascii	    "\" bs=64 2>/dev/null &&\n"
+	.ascii	  "chmod 700 \"$t\"\n}\n"
+	.ascii	  "exec \"$t\" \"$o\" \"$@\"\n"
+	.ascii	"fi\n"
+#endif
 #ifndef APE_NO_MODIFY_SELF
 //	The default behavior is: to overwrite the header in place.
 //	We prefer this because it's a tiny constant one time cost.
 //	We simply printf a 64-byte header and call execve() again.
-	.ascii	"o=\"$(command -v \"$0\")\"\n"
 #ifdef APE_BUILDSAFE
 //	This code is intended for binaries in build/bootstrap/. It
 //	causes them to not self-modify since they're checked-in to
@@ -645,6 +664,11 @@ apesh:	.ascii	"'\n#'\"\n"			# sixth edition shebang
 	.ascii	"fi\n"
 	.ascii	"exit $R\n"
 	.endobj	apesh
+#ifdef APE_LOADER
+        .section .ape.loader,"a",@progbits
+        .incbin APE_LOADER
+        .previous
+#endif /* APE_LOADER */
 #endif /* SupportsWindows() || SupportsMetal() || SupportsXnu() */
 
 #if SupportsSystemv() || SupportsMetal()
diff --git a/ape/ape.lds b/ape/ape.lds
index b772862b6..fc41a50b7 100644
--- a/ape/ape.lds
+++ b/ape/ape.lds
@@ -370,6 +370,15 @@ SECTIONS {
   } :Ram
 
 /*END:   file content that's loaded by o/s */
+/*BEGIN: payload (for now, only the APE loader) */
+  .payload ALIGN(64) : {
+    /* Loader */
+    HIDDEN(ape_loader = .);
+    KEEP(*(.ape.loader))
+    . = ALIGN(64);
+    HIDDEN(ape_loader_end = .);
+  }
+/*END: payload */
 /*BEGIN: bss memory void */
 
   .zip . : {
@@ -511,6 +520,9 @@ HIDDEN(ape_bss_filesz = 0);
 HIDDEN(ape_bss_memsz = SIZEOF(.bss));
 HIDDEN(ape_bss_align = PAGESIZE);
 
+SHSTUB2(ape_loader_dd_skip, RVA(ape_loader) / 64);
+SHSTUB2(ape_loader_dd_count, (ape_loader_end - ape_loader) / 64);
+
 #if SupportsXnu()
 SHSTUB2(ape_macho_dd_skip, RVA(ape_macho) / 8);
 SHSTUB2(ape_macho_dd_count, (ape_macho_end - ape_macho) / 8);
diff --git a/ape/ape.mk b/ape/ape.mk
index 0a75630b0..af3e277f4 100644
--- a/ape/ape.mk
+++ b/ape/ape.mk
@@ -51,8 +51,8 @@ o/ape/idata.inc:			\
 $(APE_OBJS):	$(BUILD_FILES)		\
 		ape/ape.mk
 
-o/$(MODE)/ape/ape-no-modify-self.o: ape/ape.S
-	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -DAPE_NO_MODIFY_SELF $<
+o/$(MODE)/ape/ape-no-modify-self.o: ape/ape.S o/$(MODE)/examples/loader.elf
+	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -DAPE_LOADER="\"o/$(MODE)/examples/loader.elf\"" -DAPE_NO_MODIFY_SELF $<
 
 o/$(MODE)/ape/ape-buildsafe.o: ape/ape.S
 	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -DAPE_BUILDSAFE $<