sys/conf: Remap paths for reproducibility

As in bsd.lib.mk and bsd.prog.mk, we need to remap paths in the kernel
and in kernel modules when reproducible builds are configured.  Add
directives to kern.post.mk and kmod.mk to remap the src, obj and sysroot
dirs.

For the sysroot, we need to pass the value of the SYSROOT variable to
the kernel makefiles, which involves changing Makefile.inc1.  In so
doing I reverted a portion of commit 35fb812adfc21; I can't see any harm
in passing the SYSROOT variable down.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D50953

3 files changed, 37 insertions, 5 deletions

diff --git a/Makefile.inc1 b/Makefile.inc1
index d65d1c86deac..d899f994a40d 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1051,7 +1051,7 @@ DESTDIR_MTREE=	${DISTR_MTREECMD} ${DESTDIR_MTREEFLAGS}
 METALOG_SORT_CMD=	env -i LC_COLLATE=C sort
 
 # kernel stage
-KMAKEENV=	${WMAKEENV:NSYSROOT=*}
+KMAKEENV=	${WMAKEENV}
 KMAKE=		${TIME_ENV} ${KMAKEENV} ${MAKE} ${.MAKEFLAGS} ${KERNEL_FLAGS} KERNEL=${INSTKERNNAME}
 
 #
diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index 0e4ffd92724e..1accd3fa8df4 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -372,6 +372,19 @@ _ILINKS+= x86
 _ILINKS+= i386
 .endif
 
+.if ${MK_REPRODUCIBLE_BUILD} != "no"
+PREFIX_SYSDIR=/usr/src/sys
+PREFIX_OBJDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/${KERN_IDENT}
+CFLAGS+= -ffile-prefix-map=${SYSDIR}=${PREFIX_SYSDIR}
+CFLAGS+= -ffile-prefix-map=${.OBJDIR}=${PREFIX_OBJDIR}
+.if defined(SYSROOT)
+CFLAGS+= -ffile-prefix-map=${SYSROOT}=/sysroot
+.endif
+.else
+PREFIX_SYSDIR=${SYSDIR}
+PREFIX_OBJDIR=${.OBJDIR}
+.endif
+
 # Ensure that the link exists without depending on it when it exists.
 # Ensure that debug info references the path in the source tree.
 .for _link in ${_ILINKS}
@@ -379,9 +392,9 @@ _ILINKS+= i386
 ${SRCS} ${DEPENDOBJS}: ${_link}
 .endif
 .if ${_link} == "machine"
-CFLAGS+= -fdebug-prefix-map=./machine=${SYSDIR}/${MACHINE}/include
+CFLAGS+= -fdebug-prefix-map=./machine=${PREFIX_SYSDIR}/${MACHINE}/include
 .else
-CFLAGS+= -fdebug-prefix-map=./${_link}=${SYSDIR}/${_link}/include
+CFLAGS+= -fdebug-prefix-map=./${_link}=${PREFIX_SYSDIR}/${_link}/include
 .endif
 .endfor
 
diff --git a/sys/conf/kmod.mk b/sys/conf/kmod.mk
index 645c04cdd135..0fd2d4050cf1 100644
--- a/sys/conf/kmod.mk
+++ b/sys/conf/kmod.mk
@@ -303,6 +303,25 @@ all: ${PROG}
 beforedepend: ${_ILINKS}
 beforebuild: ${_ILINKS}
 
+.if ${MK_REPRODUCIBLE_BUILD} != "no"
+PREFIX_SYSDIR=/usr/src/sys
+CFLAGS+= -ffile-prefix-map=${SYSDIR}=${PREFIX_SYSDIR}
+.if defined(KERNBUILDDIR)
+PREFIX_KERNBUILDDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/${KERNBUILDDIR:T}
+PREFIX_OBJDIR=${PREFIX_KERNBUILDDIR}/modules/usr/src/sys/modules/${.OBJDIR:T}
+CFLAGS+= -ffile-prefix-map=${KERNBUILDDIR}=${PREFIX_KERNBUILDDIR}
+.else
+PREFIX_OBJDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/modules/${.OBJDIR:T}
+.endif
+CFLAGS+= -ffile-prefix-map=${.OBJDIR}=${PREFIX_OBJDIR}
+.if defined(SYSROOT)
+CFLAGS+= -ffile-prefix-map=${SYSROOT}=/sysroot
+.endif
+.else
+PREFIX_SYSDIR=${SYSDIR}
+PREFIX_OBJDIR=${.OBJDIR}
+.endif
+
 # Ensure that the links exist without depending on it when it exists which
 # causes all the modules to be rebuilt when the directory pointed to changes.
 # Ensure that debug info references the path in the source tree.
@@ -311,9 +330,9 @@ beforebuild: ${_ILINKS}
 OBJS_DEPEND_GUESS+=	${_link}
 .endif
 .if ${_link} == "machine"
-CFLAGS+= -fdebug-prefix-map=./machine=${SYSDIR}/${MACHINE}/include
+CFLAGS+= -fdebug-prefix-map=./machine=${PREFIX_SYSDIR}/${MACHINE}/include
 .else
-CFLAGS+= -fdebug-prefix-map=./${_link}=${SYSDIR}/${_link}/include
+CFLAGS+= -fdebug-prefix-map=./${_link}=${PREFIX_SYSDIR}/${_link}/include
 .endif
 .endfor