git: 3aa0bc89c6a1 - main - libdwarf: Add a weak uncompress() symbol

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=3aa0bc89c6a1165cb16987493540372af24e760f

commit 3aa0bc89c6a1165cb16987493540372af24e760f
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2021-12-13 23:44:13 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2021-12-13 23:47:15 +0000

    libdwarf: Add a weak uncompress() symbol
    
    This works around brokenness in buildworld's bootstrapping logic: it
    uses the source tree's metadata to collect dependency info (such as,
    "libdwarf depends on libz") but links against static host libraries.
    If these two are out of sync, as is the case if one builds a commit
    prior to the introduction of the libz dependency, then the build fails
    when trying to statically link nm(1).
    
    Mitigate the problem by defining a weak uncompress() symbol which simply
    returns an error.  This ensures that the build won't fail when
    statically linking libdwarf without zlib.  The downside is that any
    tools using libdwarf without zlib will now hit a runtime error if they
    attempt to decode compressed sections, but at least they'll fail
    deterministically, and compressed debug info is only enabled by default
    in main.
    
    In particular, this fixes building of branches lacking commit
    dbf05458e3bd, such as releng branches, stable/12 and 13 and old
    revisions of main.  Previously the nm(1) build would fail with:
    
    ld: error: undefined symbol: uncompress
    >>> referenced by libdwarf_elf_init.c:233
    >>> (/usr/src/contrib/elftoolchain/libdwarf/libdwarf_elf_init.c:233)
    >>>               libdwarf_elf_init.o:(_dwarf_elf_init) in archive
    >>> /usr/lib/libdwarf.a
    
    Reported by:    dim, ler, krion
    Reviewed by:    imp, emaste
    Fixes:          dbf05458e3bd ("libdwarf: Support consumption of compressed ELF sections")
    MFC after:      1 week
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D33419
---
 contrib/elftoolchain/libdwarf/zlib_stub.c | 27 +++++++++++++++++++++++++++
 lib/libdwarf/Makefile                     |  3 ++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/contrib/elftoolchain/libdwarf/zlib_stub.c b/contrib/elftoolchain/libdwarf/zlib_stub.c
new file mode 100644
index 000000000000..173c581b31ec
--- /dev/null
+++ b/contrib/elftoolchain/libdwarf/zlib_stub.c
@@ -0,0 +1,27 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2021 The FreeBSD Foundation
+ *
+ * This software was developed by Mark Johnston under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <sys/cdefs.h>
+
+/*
+ * A hack to allow libdwarf.a to be statically linked without zlib.  This is
+ * unfortunately required for FreeBSD <= 13.0 to bootstrap build tools
+ * such as nm(1), as they use metadata from the source tree to generate the
+ * dependency list but then link with the build host's libraries.
+ */
+
+extern int uncompress(void *, unsigned long *, const void *,
+    unsigned long);
+
+int __weak_symbol
+uncompress(void *dst __unused, unsigned long *dstsz __unused,
+    const void *src __unused, unsigned long srcsz __unused)
+{
+	return (-6); /* Z_VERSION_ERROR */
+}
diff --git a/lib/libdwarf/Makefile b/lib/libdwarf/Makefile
index a3ef95b2572a..994c0bc5c1fa 100644
--- a/lib/libdwarf/Makefile
+++ b/lib/libdwarf/Makefile
@@ -73,7 +73,8 @@ SRCS=	\
 	libdwarf_reloc.c	\
 	libdwarf_rw.c		\
 	libdwarf_sections.c	\
-	libdwarf_str.c
+	libdwarf_str.c		\
+	zlib_stub.c
 
 INCS=		dwarf.h libdwarf.h