[PATCH] Fix GDB build: ELF support check & -lzstd (was: Re: [PATCH v3] binutils, gdb: support zstd compressed debug sections)

[Pedro Alves <pedro@palves.net>]

[-binutils]

On 2022-09-27 7:53 p.m., Fangrui Song via Binutils wrote:
> On Tue, Sep 27, 2022 at 11:08 AM Tom Tromey <tom@tromey.com> wrote:
>>
>>>>>>> Fangrui Song via Gdb-patches <gdb-patches@sourceware.org> writes:
>>
>>> PR29397 PR29563: The new configure option --with-zstd defaults to auto.
>>> If pkgconfig/libzstd.pc is found, define HAVE_ZSTD and support zstd
>>> compressed debug sections for most tools.
>>
>>> * bfd: for addr2line, objdump --dwarf, gdb, etc
>>> * gas: support --compress-debug-sections=zstd
>>> * ld: support ELFCOMPRESS_ZSTD input and --compress-debug-sections=zstd
>>> * objcopy: support ELFCOMPRESS_ZSTD input for
>>>   --decompress-debug-sections and --compress-debug-sections=zstd
>>> * gdb: support ELFCOMPRESS_ZSTD input.  The bfd change references zstd
>>>   symbols, so gdb has to link against -lzstd in this patch.
>>
>> This also needs some change to the sims.
>> I see failures like this with git master:
>>
>> make[4]: Entering directory '/home/tromey/gdb/build/sim/bpf'
>>   CCLD   run
>> ../../bfd/libbfd.a(compress.o):compress.c:function decompress_contents: error: undefined reference to 'ZSTD_decompress'
>> ../../bfd/libbfd.a(compress.o):compress.c:function decompress_contents: error: undefined reference to 'ZSTD_isError'
>> (unknown):176: error: undefined reference to 'ZSTD_compress'
>> (unknown):179: error: undefined reference to 'ZSTD_isError'
>> collect2: error: ld returned 1 exit status
>>
>> You'll see them all if you do a build with all sims enabled.
>>
>> thanks,
>> Tom
> 
> Thanks for the report and Tom's IRC chat with me about the
> `../../configure --enable-targets --enable-sim; make all-gdb` build.
> Tom confirmed that the latest commit `sim: Link ZSTD_LIBS` has fixed
> the problem.
> 

Hi!

I'm running into a similar gdb build/link failure with current master.

See patch below.

-- >8 --
From a461b259690b62906978450533688b71ec939310 Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Wed, 28 Sep 2022 11:33:30 +0100
Subject: [PATCH] Fix GDB build: ELF support check & -lzstd

GDB fails to build for me, on Ubuntu 20.04.  I get:

 ...
   CXXLD  gdb
 /usr/bin/ld: linux-tdep.o: in function `linux_corefile_thread(thread_info*, linux_corefile_thread_data*)':
 /home/pedro/gdb/binutils-gdb/src/gdb/linux-tdep.c:1831: undefined reference to `gcore_elf_build_thread_register_notes(gdbarch*, thread_info*, gdb_signal, bfd*, std::unique_ptr<char, gdb::xfree_deleter<char> >*, int*)'
 /usr/bin/ld: linux-tdep.o: in function `linux_make_corefile_notes(gdbarch*, bfd*, int*)':
 /home/pedro/gdb/binutils-gdb/src/gdb/linux-tdep.c:2117: undefined reference to `gcore_elf_make_tdesc_note(bfd*, std::unique_ptr<char, gdb::xfree_deleter<char> >*, int*)'
 collect2: error: ld returned 1 exit status
 make[2]: *** [Makefile:2149: gdb] Error 1
 make[2]: Leaving directory '/home/pedro/gdb/binutils-gdb/build/gdb'
 make[1]: *** [Makefile:11847: all-gdb] Error 2
 make[1]: Leaving directory '/home/pedro/gdb/binutils-gdb/build'
 make: *** [Makefile:1004: all] Error 2

Those undefined functions exist in gdb/gcore-elf.c, which is only
included in the build if GDB's configure thinks that the target you're
configuring for is an ELF target.  GDB's configure thinks my system
isn't ELF, which is incorrect.

For the ELF support check, gdb/config.log shows:

 configure:17387: checking for ELF support in BFD
 configure:17407: gcc -o conftest -I/home/pedro/gdb/binutils-gdb/src/gdb/../include -I../bfd -I/home/pedro/gdb/binutils-gdb/src/gdb/../bfd -g3 -O0      -L../bfd -L../libiberty  -lzstd   conftest.c -lbfd -liberty -lz  -lncursesw -lm -ldl  >&5
 /usr/bin/ld: ../bfd/libbfd.a(compress.o): in function `decompress_contents':
 /home/pedro/gdb/binutils-gdb/src/bfd/compress.c:42: undefined reference to `ZSTD_decompress'
 /usr/bin/ld: /home/pedro/gdb/binutils-gdb/src/bfd/compress.c:44: undefined reference to `ZSTD_isError'
 /usr/bin/ld: ../bfd/libbfd.a(compress.o): in function `bfd_compress_section_contents':
 /home/pedro/gdb/binutils-gdb/src/bfd/compress.c:195: undefined reference to `ZSTD_compress'
 /usr/bin/ld: /home/pedro/gdb/binutils-gdb/src/bfd/compress.c:198: undefined reference to `ZSTD_isError'
 collect2: error: ld returned 1 exit status
 configure:17407: $? = 1
 ...
 configure:17417: result: no

Note how above, in the gcc command line, "-lzstd" appears before
"-lbfd".  That explain the link failure.  It should appear after, like
-lz does.

This commit fixes it, by moving ZSTD_LIBS from LDFLAGS to LIBS, next
to -lz, in GDB_AC_CHECK_BFD, and regenerating gdb/configure.

Change-Id: I1f4128dde634e8ea04c9002904f1005a8b3a6863
---
 gdb/acinclude.m4 | 4 ++--
 gdb/configure    | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/gdb/acinclude.m4 b/gdb/acinclude.m4
index 28846119dcb..62fa66c7af3 100644
--- a/gdb/acinclude.m4
+++ b/gdb/acinclude.m4
@@ -234,9 +234,9 @@ AC_DEFUN([GDB_AC_CHECK_BFD], [
   # always want our bfd.
   CFLAGS="-I${srcdir}/../include -I../bfd -I${srcdir}/../bfd $CFLAGS"
   ZLIBDIR=`echo $zlibdir | sed 's,\$(top_builddir)/,,g'`
-  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $ZSTD_LIBS $LDFLAGS"
+  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $LDFLAGS"
   intl=`echo $LIBINTL | sed 's,${top_builddir}/,,g'`
-  LIBS="-lbfd -liberty -lz $intl $LIBS"
+  LIBS="-lbfd -liberty -lz $ZSTD_LIBS $intl $LIBS"
   AC_CACHE_CHECK(
     [$1],
     [$2],
diff --git a/gdb/configure b/gdb/configure
index 238b66f3c60..33677262783 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -17412,9 +17412,9 @@ WIN32LIBS="$WIN32LIBS $WIN32APILIBS"
   # always want our bfd.
   CFLAGS="-I${srcdir}/../include -I../bfd -I${srcdir}/../bfd $CFLAGS"
   ZLIBDIR=`echo $zlibdir | sed 's,\$(top_builddir)/,,g'`
-  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $ZSTD_LIBS $LDFLAGS"
+  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $LDFLAGS"
   intl=`echo $LIBINTL | sed 's,${top_builddir}/,,g'`
-  LIBS="-lbfd -liberty -lz $intl $LIBS"
+  LIBS="-lbfd -liberty -lz $ZSTD_LIBS $intl $LIBS"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ELF support in BFD" >&5
 $as_echo_n "checking for ELF support in BFD... " >&6; }
 if ${gdb_cv_var_elf+:} false; then :
@@ -17527,9 +17527,9 @@ fi
   # always want our bfd.
   CFLAGS="-I${srcdir}/../include -I../bfd -I${srcdir}/../bfd $CFLAGS"
   ZLIBDIR=`echo $zlibdir | sed 's,\$(top_builddir)/,,g'`
-  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $ZSTD_LIBS $LDFLAGS"
+  LDFLAGS="-L../bfd -L../libiberty $ZLIBDIR $LDFLAGS"
   intl=`echo $LIBINTL | sed 's,${top_builddir}/,,g'`
-  LIBS="-lbfd -liberty -lz $intl $LIBS"
+  LIBS="-lbfd -liberty -lz $ZSTD_LIBS $intl $LIBS"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for Mach-O support in BFD" >&5
 $as_echo_n "checking for Mach-O support in BFD... " >&6; }
 if ${gdb_cv_var_macho+:} false; then :

base-commit: 67d1991b785bdfef1d70cddfa0202b99b43ccce9
-- 
2.36.0