From 72f581ea8c1e3513c1be7f7c2f0e93a35ebe3b6e Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Thu, 3 Oct 2024 13:04:52 +0200
Subject: [PATCH 1/2] gh-124932: Cross builds: Distinguish between build prefix
 and host prefix

In Emscripten and wasi builds, and presumably for other cross builds, the build
file system and the host file system look different. For instance, we may want
to install into `cross-build/$TARGET/lib` and then mount that as `/lib` in the
host file system. `wasi.py` has to mess around with setting `PYTHONPATH`
because `prefix` is set to a path from the build machine. It would simplify
this if we distinguish between:

* `prefix` -- the path in the build file system where we want to install the files
* `host_prefix` -- the path in the host file system where getpath.c will look for the files

And similarly for `exec_prefix` and `host_exec_prefix`.
---
 Makefile.pre.in | 11 +++++++++--
 configure       | 25 +++++++++++++++++++++++++
 configure.ac    | 19 +++++++++++++++++++
 3 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/Makefile.pre.in b/Makefile.pre.in
index d6f75a931a3db2..1bbf1b72811d8b 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -141,6 +141,13 @@ prefix=		@prefix@
 # Install prefix for architecture-dependent files
 exec_prefix=	@exec_prefix@
 
+# For cross compilation, we distinguish between "prefix" (where we install the
+# files) and "host_prefix" (where getpath.c expects to find the files at
+# runtime)
+host_prefix= 	@host_prefix@
+host_exec_prefix= 	@host_exec_prefix@
+
+
 # Install prefix for data files
 datarootdir=    @datarootdir@
 
@@ -1740,8 +1747,8 @@ Modules/getbuildinfo.o: $(PARSER_OBJS) \
 
 Modules/getpath.o: $(srcdir)/Modules/getpath.c Python/frozen_modules/getpath.h Makefile $(PYTHON_HEADERS)
 	$(CC) -c $(PY_CORE_CFLAGS) -DPYTHONPATH='"$(PYTHONPATH)"' \
-		-DPREFIX='"$(prefix)"' \
-		-DEXEC_PREFIX='"$(exec_prefix)"' \
+		-DPREFIX='"$(host_prefix)"' \
+		-DEXEC_PREFIX='"$(host_exec_prefix)"' \
 		-DVERSION='"$(VERSION)"' \
 		-DVPATH='"$(VPATH)"' \
 		-DPLATLIBDIR='"$(PLATLIBDIR)"' \
diff --git a/configure b/configure
index b11f41d5379958..d6ea8f079ab696 100755
--- a/configure
+++ b/configure
@@ -1003,6 +1003,8 @@ LIPO_INTEL64_FLAGS
 LIPO_32BIT_FLAGS
 ARCH_RUN_32BIT
 UNIVERSALSDK
+host_exec_prefix
+host_prefix
 MACHDEP
 PKG_CONFIG_LIBDIR
 PKG_CONFIG_PATH
@@ -4105,6 +4107,29 @@ fi
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: \"$MACHDEP\"" >&5
 printf "%s\n" "\"$MACHDEP\"" >&6; }
 
+
+if test -z "$host_prefix"; then
+  case $ac_sys_system in #(
+  Emscripten) :
+    host_prefix=/ ;; #(
+  *) :
+    host_prefix='${prefix}'
+   ;;
+esac
+fi
+
+
+if test -z "$host_exec_prefix"; then
+  case $ac_sys_system in #(
+  Emscripten) :
+    host_exec_prefix=$host_prefix ;; #(
+  *) :
+    host_exec_prefix='${exec_prefix}'
+   ;;
+esac
+fi
+
+
 # On cross-compile builds, configure will look for a host-specific compiler by
 # prepending the user-provided host triple to the required binary name.
 #
diff --git a/configure.ac b/configure.ac
index d5bc739c34c90f..835050f8f61f34 100644
--- a/configure.ac
+++ b/configure.ac
@@ -379,6 +379,25 @@ then
 fi
 AC_MSG_RESULT(["$MACHDEP"])
 
+dnl For cross compilation, we distinguish between "prefix" (where we install the
+dnl files) and "host_prefix" (where we expect to find the files at runtime)
+
+if test -z "$host_prefix"; then
+  AS_CASE([$ac_sys_system],
+    [Emscripten], [host_prefix=/],
+    [host_prefix='${prefix}']
+  )
+fi
+AC_SUBST([host_prefix])
+
+if test -z "$host_exec_prefix"; then
+  AS_CASE([$ac_sys_system],
+    [Emscripten], [host_exec_prefix=$host_prefix],
+    [host_exec_prefix='${exec_prefix}']
+  )
+fi
+AC_SUBST([host_exec_prefix])
+
 # On cross-compile builds, configure will look for a host-specific compiler by
 # prepending the user-provided host triple to the required binary name.
 #

From 11d379345e3dc00c2bee69429b00727ee628997c Mon Sep 17 00:00:00 2001
From: Hood Chatham <roberthoodchatham@gmail.com>
Date: Fri, 25 Oct 2024 17:21:33 +0200
Subject: [PATCH 2/2] Add news entry

---
 .../next/Build/2024-10-25-17-20-50.gh-issue-124932.F-aNuS.rst | 4 ++++
 1 file changed, 4 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Build/2024-10-25-17-20-50.gh-issue-124932.F-aNuS.rst

diff --git a/Misc/NEWS.d/next/Build/2024-10-25-17-20-50.gh-issue-124932.F-aNuS.rst b/Misc/NEWS.d/next/Build/2024-10-25-17-20-50.gh-issue-124932.F-aNuS.rst
new file mode 100644
index 00000000000000..10c4171dc14a64
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2024-10-25-17-20-50.gh-issue-124932.F-aNuS.rst
@@ -0,0 +1,4 @@
+For cross builds, there is now support for having a different install
+``prefix`` than the ``host_prefix`` used by ``getpath.py``. This is set to ``/`` by
+default for Emscripten, on other platforms the default behavior is the same
+as before.