git: 4f81c42fbd76 - main - share/mk: Substitute reproducible prefixes in dwarf info

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=4f81c42fbd76e25c9fe696fa08296b79c55fbf09

commit 4f81c42fbd76e25c9fe696fa08296b79c55fbf09
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-08-21 14:06:34 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-08-21 15:56:23 +0000

    share/mk: Substitute reproducible prefixes in dwarf info
    
    Ensure that worlds/releases built from different source paths are
    reproducible.  Currently they are not since src and obj paths are
    embedded in DWARF info.  There are some uses of __FILE__ in the src tree
    as well, and they are similarly handled by this change.
    
    Use /usr/src and /usr/obj as the canonical src and obj paths when
    WITH_REPRODUCIBLE_BUILD is defined.  Define a DEBUG_PREFIX variable
    which is used to ask the compiler to substitute paths in output files
    using -ffile-prefix-map.
    
    Compat builds (i.e., lib32) complicate things since they override
    OBJROOT to point to obj-${compat} but still refer to headers from the
    native objroot (e.g., llvm headers).
    
    MFC after:      1 month
    Sponsored by:   The FreeBSD Foundation
    Sponsored by:   Klara, Inc.
    Differential Revision:  https://reviews.freebsd.org/D50951
---
 share/mk/bsd.debug.mk | 22 ++++++++++++++++++++++
 share/mk/bsd.opts.mk  |  1 +
 2 files changed, 23 insertions(+)

diff --git a/share/mk/bsd.debug.mk b/share/mk/bsd.debug.mk
index fc80bc103061..cf2fb4356aef 100644
--- a/share/mk/bsd.debug.mk
+++ b/share/mk/bsd.debug.mk
@@ -13,6 +13,28 @@ CFLAGS+= -DNDEBUG
 MK_WERROR=	no
 .endif
 
+# If reproducible build mode is enabled, map the root of the source
+# directory to /usr/src and the root of the object directory to
+# /usr/obj.
+.if ${MK_REPRODUCIBLE_BUILD} != "no" && !defined(DEBUG_PREFIX)
+.if defined(SRCTOP)
+DEBUG_PREFIX+= ${SRCTOP:S,/$,,}=/usr/src
+.endif
+.if defined(OBJROOT)
+# Strip off compat subdirectories, e.g., /usr/obj/usr/src/amd64.amd64/obj-lib32
+# becomes /usr/obj/usr/src/amd64.amd64, since object files compiled there might
+# refer to something outside the root.
+DEBUG_PREFIX+= ${OBJROOT:S,/$,,:C,/obj-[^/]*$,,}=/usr/obj
+.endif
+.endif
+
+.if defined(DEBUG_PREFIX)
+.for map in ${DEBUG_PREFIX}
+CFLAGS+= -ffile-prefix-map=${map}
+CXXFLAGS+= -ffile-prefix-map=${map}
+.endfor
+.endif
+
 .if defined(DEBUG_FLAGS)
 CFLAGS+=${DEBUG_FLAGS}
 CXXFLAGS+=${DEBUG_FLAGS}
diff --git a/share/mk/bsd.opts.mk b/share/mk/bsd.opts.mk
index 85247d733a14..439924d0d596 100644
--- a/share/mk/bsd.opts.mk
+++ b/share/mk/bsd.opts.mk
@@ -78,6 +78,7 @@ __DEFAULT_NO_OPTIONS = \
     CCACHE_BUILD \
     CTF \
     INSTALL_AS_USER \
+    REPRODUCIBLE_BUILD \
     RETPOLINE \
     RUN_TESTS \
     STALE_STAGED \