binutils, gdb: support zstd compressed debug sections

PR29397 PR29563: Add new configure option --with-zstd which 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.

If zstd is not supported, ELFCOMPRESS_ZSTD input triggers an error.  We
can avoid HAVE_ZSTD if binutils-gdb imports zstd/ like zlib/, but this
is too heavyweight, so don't do it for now.

```
% ld/ld-new a.o
ld/ld-new: a.o: section .debug_abbrev is compressed with zstd, but BFD is not built with zstd support
...

% ld/ld-new a.o --compress-debug-sections=zstd
ld/ld-new: --compress-debug-sections=zstd: ld is not built with zstd support

% binutils/objcopy --compress-debug-sections=zstd a.o b.o
binutils/objcopy: --compress-debug-sections=zstd: binutils is not built with zstd support

% binutils/objcopy b.o --decompress-debug-sections
binutils/objcopy: zstd.o: section .debug_abbrev is compressed with zstd, but BFD is not built with zstd support
...
```

13 files changed, 383 insertions, 43 deletions

diff --git a/bfd/Makefile.am b/bfd/Makefile.am
index a5652b2..98a487b 100644
--- a/bfd/Makefile.am
+++ b/bfd/Makefile.am
@@ -57,7 +57,7 @@ ZLIBINC = @zlibinc@
 
 WARN_CFLAGS = @WARN_CFLAGS@
 NO_WERROR = @NO_WERROR@
-AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC)
+AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC) $(ZSTD_CFLAGS)
 AM_CPPFLAGS = -DBINDIR='"$(bindir)"' -DLIBDIR='"$(libdir)"' @LARGEFILE_CPPFLAGS@
 if PLUGINS
 bfdinclude_HEADERS += $(INCDIR)/plugin-api.h
@@ -776,7 +776,7 @@ ofiles: stamp-ofiles ; @true
 libbfd_la_SOURCES = $(BFD32_LIBS_CFILES)
 EXTRA_libbfd_la_SOURCES = $(CFILES)
 libbfd_la_DEPENDENCIES = $(OFILES) ofiles
-libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB)
+libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB) $(ZSTD_LIBS)
 libbfd_la_LDFLAGS += -release `cat libtool-soversion` @SHARED_LDFLAGS@
 
 # libtool will build .libs/libbfd.a.  We create libbfd.a in the build
diff --git a/bfd/Makefile.in b/bfd/Makefile.in
index 83d6865..3c9ebf3 100644
--- a/bfd/Makefile.in
+++ b/bfd/Makefile.in
@@ -122,10 +122,12 @@ am__aclocal_m4_deps = $(top_srcdir)/../config/acx.m4 \
 	$(top_srcdir)/../config/lead-dot.m4 \
 	$(top_srcdir)/../config/nls.m4 \
 	$(top_srcdir)/../config/override.m4 \
+	$(top_srcdir)/../config/pkg.m4 \
 	$(top_srcdir)/../config/plugins.m4 \
 	$(top_srcdir)/../config/po.m4 \
 	$(top_srcdir)/../config/progtest.m4 \
-	$(top_srcdir)/../config/zlib.m4 $(top_srcdir)/../libtool.m4 \
+	$(top_srcdir)/../config/zlib.m4 \
+	$(top_srcdir)/../config/zstd.m4 $(top_srcdir)/../libtool.m4 \
 	$(top_srcdir)/../ltoptions.m4 $(top_srcdir)/../ltsugar.m4 \
 	$(top_srcdir)/../ltversion.m4 $(top_srcdir)/../lt~obsolete.m4 \
 	$(top_srcdir)/bfd.m4 $(top_srcdir)/warning.m4 \
@@ -399,6 +401,9 @@ PACKAGE_URL = @PACKAGE_URL@
 PACKAGE_VERSION = @PACKAGE_VERSION@
 PATH_SEPARATOR = @PATH_SEPARATOR@
 PKGVERSION = @PKGVERSION@
+PKG_CONFIG = @PKG_CONFIG@
+PKG_CONFIG_LIBDIR = @PKG_CONFIG_LIBDIR@
+PKG_CONFIG_PATH = @PKG_CONFIG_PATH@
 POSUB = @POSUB@
 RANLIB = @RANLIB@
 REPORT_BUGS_TEXI = @REPORT_BUGS_TEXI@
@@ -416,6 +421,8 @@ WARN_CFLAGS = @WARN_CFLAGS@
 WARN_CFLAGS_FOR_BUILD = @WARN_CFLAGS_FOR_BUILD@
 WARN_WRITE_STRINGS = @WARN_WRITE_STRINGS@
 XGETTEXT = @XGETTEXT@
+ZSTD_CFLAGS = @ZSTD_CFLAGS@
+ZSTD_LIBS = @ZSTD_LIBS@
 abs_builddir = @abs_builddir@
 abs_srcdir = @abs_srcdir@
 abs_top_builddir = @abs_top_builddir@
@@ -520,7 +527,7 @@ libbfd_la_LDFLAGS = $(am__append_1) -release `cat libtool-soversion` \
 # case both are empty.
 ZLIB = @zlibdir@ -lz
 ZLIBINC = @zlibinc@
-AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC)
+AM_CFLAGS = $(WARN_CFLAGS) $(ZLIBINC) $(ZSTD_CFLAGS)
 AM_CPPFLAGS = -DBINDIR='"$(bindir)"' -DLIBDIR='"$(libdir)"' \
 	@LARGEFILE_CPPFLAGS@ @HDEFINES@ @COREFLAG@ @TDEFINES@ \
 	$(CSEARCH) $(CSWITCHES) $(HAVEVECS) @INCINTL@
@@ -1199,7 +1206,7 @@ OFILES = $(BFD_BACKENDS) $(BFD_MACHINES) @COREFILE@ @bfd64_libs@
 libbfd_la_SOURCES = $(BFD32_LIBS_CFILES)
 EXTRA_libbfd_la_SOURCES = $(CFILES)
 libbfd_la_DEPENDENCIES = $(OFILES) ofiles
-libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB)
+libbfd_la_LIBADD = `cat ofiles` @SHARED_LIBADD@ $(LIBDL) $(ZLIB) $(ZSTD_LIBS)
 
 # libtool will build .libs/libbfd.a.  We create libbfd.a in the build
 # directory so that we don't have to convert all the programs that use
diff --git a/bfd/aclocal.m4 b/bfd/aclocal.m4
index 0f8aa1d..09b849d 100644
--- a/bfd/aclocal.m4
+++ b/bfd/aclocal.m4
@@ -1176,10 +1176,12 @@ m4_include([../config/largefile.m4])
 m4_include([../config/lead-dot.m4])
 m4_include([../config/nls.m4])
 m4_include([../config/override.m4])
+m4_include([../config/pkg.m4])
 m4_include([../config/plugins.m4])
 m4_include([../config/po.m4])
 m4_include([../config/progtest.m4])
 m4_include([../config/zlib.m4])
+m4_include([../config/zstd.m4])
 m4_include([../libtool.m4])
 m4_include([../ltoptions.m4])
 m4_include([../ltsugar.m4])
diff --git a/bfd/bfd-in.h b/bfd/bfd-in.h
index 8605056..4765ea8 100644
--- a/bfd/bfd-in.h
+++ b/bfd/bfd-in.h
@@ -342,7 +342,8 @@ enum compressed_debug_section_type
   COMPRESS_DEBUG_NONE = 0,
   COMPRESS_DEBUG = 1 << 0,
   COMPRESS_DEBUG_GNU_ZLIB = COMPRESS_DEBUG | 1 << 1,
-  COMPRESS_DEBUG_GABI_ZLIB = COMPRESS_DEBUG | 1 << 2
+  COMPRESS_DEBUG_GABI_ZLIB = COMPRESS_DEBUG | 1 << 2,
+  COMPRESS_DEBUG_ZSTD = COMPRESS_DEBUG | 1 << 3
 };
 
 /* This structure is used to keep track of stabs in sections
diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 79fcc4e..5c80956 100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -349,7 +349,8 @@ enum compressed_debug_section_type
   COMPRESS_DEBUG_NONE = 0,
   COMPRESS_DEBUG = 1 << 0,
   COMPRESS_DEBUG_GNU_ZLIB = COMPRESS_DEBUG | 1 << 1,
-  COMPRESS_DEBUG_GABI_ZLIB = COMPRESS_DEBUG | 1 << 2
+  COMPRESS_DEBUG_GABI_ZLIB = COMPRESS_DEBUG | 1 << 2,
+  COMPRESS_DEBUG_ZSTD = COMPRESS_DEBUG | 1 << 3
 };
 
 /* This structure is used to keep track of stabs in sections
@@ -962,7 +963,8 @@ typedef struct bfd_section
   unsigned int compress_status : 2;
 #define COMPRESS_SECTION_NONE    0
 #define COMPRESS_SECTION_DONE    1
-#define DECOMPRESS_SECTION_SIZED 2
+#define DECOMPRESS_SECTION_ZLIB  2
+#define DECOMPRESS_SECTION_ZSTD  3
 
   /* The following flags are used by the ELF linker. */
 
@@ -6637,12 +6639,14 @@ struct bfd
 #define BFD_ARCHIVE_FULL_PATH  0x100000
 
 #define BFD_CLOSED_BY_CACHE    0x200000
+  /* Compress sections in this BFD with SHF_COMPRESSED zstd.  */
+#define BFD_COMPRESS_ZSTD      0x400000
 
   /* Flags bits to be saved in bfd_preserve_save.  */
 #define BFD_FLAGS_SAVED \
   (BFD_IN_MEMORY | BFD_COMPRESS | BFD_DECOMPRESS | BFD_LINKER_CREATED \
    | BFD_PLUGIN | BFD_COMPRESS_GABI | BFD_CONVERT_ELF_COMMON \
-   | BFD_USE_ELF_STT_COMMON)
+   | BFD_USE_ELF_STT_COMMON | BFD_COMPRESS_ZSTD)
 
   /* Flags bits which are for BFD use only.  */
 #define BFD_FLAGS_FOR_BFD_USE_MASK \
@@ -7271,6 +7275,7 @@ void bfd_update_compression_header
 
 bool bfd_check_compression_header
    (bfd *abfd, bfd_byte *contents, asection *sec,
+    unsigned int *ch_type,
     bfd_size_type *uncompressed_size,
     unsigned int *uncompressed_alignment_power);
 
diff --git a/bfd/bfd.c b/bfd/bfd.c
index 0a21db1..5f2033b 100644
--- a/bfd/bfd.c
+++ b/bfd/bfd.c
@@ -177,12 +177,15 @@ CODE_FRAGMENT
 .#define BFD_ARCHIVE_FULL_PATH  0x100000
 .
 .#define BFD_CLOSED_BY_CACHE    0x200000
+
+.  {* Compress sections in this BFD with SHF_COMPRESSED zstd.  *}
+.#define BFD_COMPRESS_ZSTD      0x400000
 .
 .  {* Flags bits to be saved in bfd_preserve_save.  *}
 .#define BFD_FLAGS_SAVED \
 .  (BFD_IN_MEMORY | BFD_COMPRESS | BFD_DECOMPRESS | BFD_LINKER_CREATED \
 .   | BFD_PLUGIN | BFD_COMPRESS_GABI | BFD_CONVERT_ELF_COMMON \
-.   | BFD_USE_ELF_STT_COMMON)
+.   | BFD_USE_ELF_STT_COMMON | BFD_COMPRESS_ZSTD)
 .
 .  {* Flags bits which are for BFD use only.  *}
 .#define BFD_FLAGS_FOR_BFD_USE_MASK \
@@ -2500,6 +2503,9 @@ bfd_update_compression_header (bfd *abfd, bfd_byte *contents,
 	{
 	  const struct elf_backend_data *bed = get_elf_backend_data (abfd);
 	  struct bfd_elf_section_data * esd = elf_section_data (sec);
+	  const unsigned int ch_type = abfd->flags & BFD_COMPRESS_ZSTD
+					   ? ELFCOMPRESS_ZSTD
+					   : ELFCOMPRESS_ZLIB;
 
 	  /* Set the SHF_COMPRESSED bit.  */
 	  elf_section_flags (sec) |= SHF_COMPRESSED;
@@ -2507,7 +2513,7 @@ bfd_update_compression_header (bfd *abfd, bfd_byte *contents,
 	  if (bed->s->elfclass == ELFCLASS32)
 	    {
 	      Elf32_External_Chdr *echdr = (Elf32_External_Chdr *) contents;
-	      bfd_put_32 (abfd, ELFCOMPRESS_ZLIB, &echdr->ch_type);
+	      bfd_put_32 (abfd, ch_type, &echdr->ch_type);
 	      bfd_put_32 (abfd, sec->size, &echdr->ch_size);
 	      bfd_put_32 (abfd, 1u << sec->alignment_power,
 			  &echdr->ch_addralign);
@@ -2518,7 +2524,7 @@ bfd_update_compression_header (bfd *abfd, bfd_byte *contents,
 	  else
 	    {
 	      Elf64_External_Chdr *echdr = (Elf64_External_Chdr *) contents;
-	      bfd_put_32 (abfd, ELFCOMPRESS_ZLIB, &echdr->ch_type);
+	      bfd_put_32 (abfd, ch_type, &echdr->ch_type);
 	      bfd_put_32 (abfd, 0, &echdr->ch_reserved);
 	      bfd_put_64 (abfd, sec->size, &echdr->ch_size);
 	      bfd_put_64 (abfd, UINT64_C (1) << sec->alignment_power,
@@ -2553,14 +2559,15 @@ bfd_update_compression_header (bfd *abfd, bfd_byte *contents,
    SYNOPSIS
 	bool bfd_check_compression_header
 	  (bfd *abfd, bfd_byte *contents, asection *sec,
+	  unsigned int *ch_type,
 	  bfd_size_type *uncompressed_size,
 	  unsigned int *uncompressed_alignment_power);
 
 DESCRIPTION
-	Check the compression header at CONTENTS of SEC in ABFD and
-	store the uncompressed size in UNCOMPRESSED_SIZE and the
-	uncompressed data alignment in UNCOMPRESSED_ALIGNMENT_POWER
-	if the compression header is valid.
+	Check the compression header at CONTENTS of SEC in ABFD and store the
+	ch_type in CH_TYPE, uncompressed size in UNCOMPRESSED_SIZE, and the
+	uncompressed data alignment in UNCOMPRESSED_ALIGNMENT_POWER if the
+	compression header is valid.
 
 RETURNS
 	Return TRUE if the compression header is valid.
@@ -2569,6 +2576,7 @@ RETURNS
 bool
 bfd_check_compression_header (bfd *abfd, bfd_byte *contents,
 			      asection *sec,
+			      unsigned int *ch_type,
 			      bfd_size_type *uncompressed_size,
 			      unsigned int *uncompressed_alignment_power)
 {
@@ -2591,7 +2599,9 @@ bfd_check_compression_header (bfd *abfd, bfd_byte *contents,
 	  chdr.ch_size = bfd_get_64 (abfd, &echdr->ch_size);
 	  chdr.ch_addralign = bfd_get_64 (abfd, &echdr->ch_addralign);
 	}
-      if (chdr.ch_type == ELFCOMPRESS_ZLIB
+      *ch_type = chdr.ch_type;
+      if ((chdr.ch_type == ELFCOMPRESS_ZLIB
+	   || chdr.ch_type == ELFCOMPRESS_ZSTD)
 	  && chdr.ch_addralign == (chdr.ch_addralign & -chdr.ch_addralign))
 	{
 	  *uncompressed_size = chdr.ch_size;
diff --git a/bfd/compress.c b/bfd/compress.c
index b2e3982..0e75b68 100644
--- a/bfd/compress.c
+++ b/bfd/compress.c
@@ -20,18 +20,31 @@
 
 #include "sysdep.h"
 #include <zlib.h>
+#ifdef HAVE_ZSTD
+#include <zstd.h>
+#endif
 #include "bfd.h"
+#include "elf-bfd.h"
 #include "libbfd.h"
 #include "safe-ctype.h"
 
 #define MAX_COMPRESSION_HEADER_SIZE 24
 
 static bool
-decompress_contents (bfd_byte *compressed_buffer,
+decompress_contents (bool is_zstd, bfd_byte *compressed_buffer,
 		     bfd_size_type compressed_size,
 		     bfd_byte *uncompressed_buffer,
 		     bfd_size_type uncompressed_size)
 {
+  if (is_zstd)
+    {
+#ifdef HAVE_ZSTD
+      size_t ret = ZSTD_decompress (uncompressed_buffer, uncompressed_size,
+				    compressed_buffer, compressed_size);
+      return !ZSTD_isError (ret);
+#endif
+    }
+
   z_stream strm;
   int rc;
 
@@ -69,7 +82,7 @@ decompress_contents (bfd_byte *compressed_buffer,
 }
 
 /* Compress data of the size specified in @var{uncompressed_size}
-   and pointed to by @var{uncompressed_buffer} using zlib and store
+   and pointed to by @var{uncompressed_buffer} using zlib/zstd and store
    as the contents field.  This function assumes the contents
    field was allocated using bfd_malloc() or equivalent.
 
@@ -150,9 +163,10 @@ bfd_compress_section_contents (bfd *abfd, sec_ptr sec,
       sec->size = orig_uncompressed_size;
       if (decompress)
 	{
-	  if (!decompress_contents (uncompressed_buffer
-				    + orig_compression_header_size,
-				    zlib_size, buffer, buffer_size))
+	  if (!decompress_contents (
+		  sec->compress_status == DECOMPRESS_SECTION_ZSTD,
+		  uncompressed_buffer + orig_compression_header_size,
+		  zlib_size, buffer, buffer_size))
 	    {
 	      bfd_set_error (bfd_error_bad_value);
 	      bfd_release (abfd, buffer);
@@ -175,10 +189,23 @@ bfd_compress_section_contents (bfd *abfd, sec_ptr sec,
     }
   else
     {
-      if (compress ((Bytef*) buffer + header_size,
-		    &compressed_size,
-		    (const Bytef*) uncompressed_buffer,
-		    uncompressed_size) != Z_OK)
+      if (abfd->flags & BFD_COMPRESS_ZSTD)
+	{
+#if HAVE_ZSTD
+	  compressed_size = ZSTD_compress (
+		  buffer + header_size, compressed_size, uncompressed_buffer,
+		  uncompressed_size, ZSTD_CLEVEL_DEFAULT);
+	  if (ZSTD_isError (compressed_size))
+	    {
+	      bfd_release (abfd, buffer);
+	      bfd_set_error (bfd_error_bad_value);
+	      return 0;
+	    }
+#endif
+	}
+      else if (compress ((Bytef *)buffer + header_size, &compressed_size,
+			 (const Bytef *)uncompressed_buffer, uncompressed_size)
+	       != Z_OK)
 	{
 	  bfd_release (abfd, buffer);
 	  bfd_set_error (bfd_error_bad_value);
@@ -237,6 +264,7 @@ bfd_get_full_section_contents (bfd *abfd, sec_ptr sec, bfd_byte **ptr)
   bfd_size_type save_rawsize;
   bfd_byte *compressed_buffer;
   unsigned int compression_header_size;
+  const unsigned int compress_status = sec->compress_status;
 
   if (abfd->direction != write_direction && sec->rawsize != 0)
     sz = sec->rawsize;
@@ -248,7 +276,7 @@ bfd_get_full_section_contents (bfd *abfd, sec_ptr sec, bfd_byte **ptr)
       return true;
     }
 
-  switch (sec->compress_status)
+  switch (compress_status)
     {
     case COMPRESS_SECTION_NONE:
       if (p == NULL)
@@ -298,7 +326,8 @@ bfd_get_full_section_contents (bfd *abfd, sec_ptr sec, bfd_byte **ptr)
       *ptr = p;
       return true;
 
-    case DECOMPRESS_SECTION_SIZED:
+    case DECOMPRESS_SECTION_ZLIB:
+    case DECOMPRESS_SECTION_ZSTD:
       /* Read in the full compressed section contents.  */
       compressed_buffer = (bfd_byte *) bfd_malloc (sec->compressed_size);
       if (compressed_buffer == NULL)
@@ -316,7 +345,7 @@ bfd_get_full_section_contents (bfd *abfd, sec_ptr sec, bfd_byte **ptr)
       /* Restore rawsize and size.  */
       sec->rawsize = save_rawsize;
       sec->size = save_size;
-      sec->compress_status = DECOMPRESS_SECTION_SIZED;
+      sec->compress_status = compress_status;
       if (!ret)
 	goto fail_compressed;
 
@@ -330,8 +359,10 @@ bfd_get_full_section_contents (bfd *abfd, sec_ptr sec, bfd_byte **ptr)
 	/* Set header size to the zlib header size if it is a
 	   SHF_COMPRESSED section.  */
 	compression_header_size = 12;
-      if (!decompress_contents (compressed_buffer + compression_header_size,
-				sec->compressed_size - compression_header_size, p, sz))
+      bool is_zstd = compress_status == DECOMPRESS_SECTION_ZSTD;
+      if (!decompress_contents (
+	      is_zstd, compressed_buffer + compression_header_size,
+	      sec->compressed_size - compression_header_size, p, sz))
 	{
 	  bfd_set_error (bfd_error_bad_value);
 	  if (p != *ptr)
@@ -381,7 +412,8 @@ DESCRIPTION
 void
 bfd_cache_section_contents (asection *sec, void *contents)
 {
-  if (sec->compress_status == DECOMPRESS_SECTION_SIZED)
+  if (sec->compress_status == DECOMPRESS_SECTION_ZLIB
+      || sec->compress_status == DECOMPRESS_SECTION_ZSTD)
     sec->compress_status = COMPRESS_SECTION_DONE;
   sec->contents = contents;
   sec->flags |= SEC_IN_MEMORY;
@@ -418,6 +450,7 @@ bfd_is_section_compressed_with_header (bfd *abfd, sec_ptr sec,
   int compression_header_size;
   int header_size;
   unsigned int saved = sec->compress_status;
+  unsigned int ch_type;
   bool compressed;
 
   *uncompressed_align_pow_p = 0;
@@ -448,7 +481,7 @@ bfd_is_section_compressed_with_header (bfd *abfd, sec_ptr sec,
     {
       if (compression_header_size != 0)
 	{
-	  if (!bfd_check_compression_header (abfd, header, sec,
+	  if (!bfd_check_compression_header (abfd, header, sec, &ch_type,
 					     uncompressed_size_p,
 					     uncompressed_align_pow_p))
 	    compression_header_size = -1;
@@ -507,7 +540,7 @@ SYNOPSIS
 DESCRIPTION
 	Record compressed section size, update section size with
 	decompressed size and set compress_status to
-	DECOMPRESS_SECTION_SIZED.
+	DECOMPRESS_SECTION_{ZLIB,ZSTD}.
 
 	Return @code{FALSE} if the section is not a valid compressed
 	section.  Otherwise, return @code{TRUE}.
@@ -521,6 +554,7 @@ bfd_init_section_decompress_status (bfd *abfd, sec_ptr sec)
   int header_size;
   bfd_size_type uncompressed_size;
   unsigned int uncompressed_alignment_power = 0;
+  unsigned int ch_type;
   z_stream strm;
 
   compression_header_size = bfd_get_compression_header_size (abfd, sec);
@@ -550,6 +584,7 @@ bfd_init_section_decompress_status (bfd *abfd, sec_ptr sec)
       uncompressed_size = bfd_getb64 (header + 4);
     }
   else if (!bfd_check_compression_header (abfd, header, sec,
+					  &ch_type,
 					  &uncompressed_size,
 					  &uncompressed_alignment_power))
     {
@@ -569,7 +604,8 @@ bfd_init_section_decompress_status (bfd *abfd, sec_ptr sec)
   sec->compressed_size = sec->size;
   sec->size = uncompressed_size;
   bfd_set_section_alignment (sec, uncompressed_alignment_power);
-  sec->compress_status = DECOMPRESS_SECTION_SIZED;
+  sec->compress_status = (ch_type == ELFCOMPRESS_ZSTD
+			  ? DECOMPRESS_SECTION_ZSTD : DECOMPRESS_SECTION_ZLIB);
 
   return true;
 }
diff --git a/bfd/config.in b/bfd/config.in
index f54a3ca..a59304e 100644
--- a/bfd/config.in
+++ b/bfd/config.in
@@ -232,6 +232,9 @@
 /* Define to 1 if you have the <windows.h> header file. */
 #undef HAVE_WINDOWS_H
 
+/* Define to 1 if zstd is enabled. */
+#undef HAVE_ZSTD
+
 /* Define to the sub-directory in which libtool stores uninstalled libraries.
    */
 #undef LT_OBJDIR
diff --git a/bfd/configure b/bfd/configure
index 075d2ee..d905a7b 100755
--- a/bfd/configure
+++ b/bfd/configure
@@ -652,6 +652,11 @@ TDEFINES
 SHARED_LIBADD
 SHARED_LDFLAGS
 LIBM
+ZSTD_LIBS
+ZSTD_CFLAGS
+PKG_CONFIG_LIBDIR
+PKG_CONFIG_PATH
+PKG_CONFIG
 zlibinc
 zlibdir
 EXEEXT_FOR_BUILD
@@ -839,6 +844,7 @@ enable_maintainer_mode
 enable_install_libbfd
 enable_nls
 with_system_zlib
+with_zstd
 '
       ac_precious_vars='build_alias
 host_alias
@@ -848,7 +854,12 @@ CFLAGS
 LDFLAGS
 LIBS
 CPPFLAGS
-CPP'
+CPP
+PKG_CONFIG
+PKG_CONFIG_PATH
+PKG_CONFIG_LIBDIR
+ZSTD_CFLAGS
+ZSTD_LIBS'
 
 
 # Initialize some variables set by options.
@@ -1511,6 +1522,8 @@ Optional Packages:
                           Binutils"
   --with-bugurl=URL       Direct users to URL to report a bug
   --with-system-zlib      use installed libz
+  --with-zstd             support zstd compressed debug sections
+                          (default=auto)
 
 Some influential environment variables:
   CC          C compiler command
@@ -1521,6 +1534,13 @@ Some influential environment variables:
   CPPFLAGS    (Objective) C/C++ preprocessor flags, e.g. -I<include dir> if
               you have headers in a nonstandard directory <include dir>
   CPP         C preprocessor
+  PKG_CONFIG  path to pkg-config utility
+  PKG_CONFIG_PATH
+              directories to add to pkg-config's search path
+  PKG_CONFIG_LIBDIR
+              path overriding pkg-config's built-in search path
+  ZSTD_CFLAGS C compiler flags for ZSTD, overriding pkg-config
+  ZSTD_LIBS   linker flags for ZSTD, overriding pkg-config
 
 Use these variables to override the choices made by `configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -11086,7 +11106,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11089 "configure"
+#line 11109 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11192,7 +11212,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11195 "configure"
+#line 11215 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12995,7 +13015,7 @@ $as_echo "#define USE_BINARY_FOPEN 1" >>confdefs.h
  ;;
 esac
 
-# Link in zlib if we can.  This allows us to read compressed debug sections.
+# Link in zlib/zstd if we can.  This allows us to read compressed debug sections.
 # This is used only by compress.c.
 
   # Use the system's zlib library.
@@ -13015,6 +13035,246 @@ fi
 
 
 
+
+
+
+
+
+
+if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
+	if test -n "$ac_tool_prefix"; then
+  # Extract the first word of "${ac_tool_prefix}pkg-config", so it can be a program name with args.
+set dummy ${ac_tool_prefix}pkg-config; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_PKG_CONFIG+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $PKG_CONFIG in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_PKG_CONFIG="$PKG_CONFIG" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_PKG_CONFIG="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+PKG_CONFIG=$ac_cv_path_PKG_CONFIG
+if test -n "$PKG_CONFIG"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PKG_CONFIG" >&5
+$as_echo "$PKG_CONFIG" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
+if test -z "$ac_cv_path_PKG_CONFIG"; then
+  ac_pt_PKG_CONFIG=$PKG_CONFIG
+  # Extract the first word of "pkg-config", so it can be a program name with args.
+set dummy pkg-config; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_ac_pt_PKG_CONFIG+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $ac_pt_PKG_CONFIG in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_ac_pt_PKG_CONFIG="$ac_pt_PKG_CONFIG" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_ac_pt_PKG_CONFIG="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+ac_pt_PKG_CONFIG=$ac_cv_path_ac_pt_PKG_CONFIG
+if test -n "$ac_pt_PKG_CONFIG"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_pt_PKG_CONFIG" >&5
+$as_echo "$ac_pt_PKG_CONFIG" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+  if test "x$ac_pt_PKG_CONFIG" = x; then
+    PKG_CONFIG=""
+  else
+    case $cross_compiling:$ac_tool_warned in
+yes:)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
+$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
+ac_tool_warned=yes ;;
+esac
+    PKG_CONFIG=$ac_pt_PKG_CONFIG
+  fi
+else
+  PKG_CONFIG="$ac_cv_path_PKG_CONFIG"
+fi
+
+fi
+if test -n "$PKG_CONFIG"; then
+	_pkg_min_version=0.9.0
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking pkg-config is at least version $_pkg_min_version" >&5
+$as_echo_n "checking pkg-config is at least version $_pkg_min_version... " >&6; }
+	if $PKG_CONFIG --atleast-pkgconfig-version $_pkg_min_version; then
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+	else
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+		PKG_CONFIG=""
+	fi
+fi
+
+
+# Check whether --with-zstd was given.
+if test "${with_zstd+set}" = set; then :
+  withval=$with_zstd;
+else
+  with_zstd=auto
+fi
+
+
+if test "$with_zstd" != no; then
+
+pkg_failed=no
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for libzstd" >&5
+$as_echo_n "checking for libzstd... " >&6; }
+
+if test -n "$ZSTD_CFLAGS"; then
+    pkg_cv_ZSTD_CFLAGS="$ZSTD_CFLAGS"
+ elif test -n "$PKG_CONFIG"; then
+    if test -n "$PKG_CONFIG" && \
+    { { $as_echo "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libzstd\""; } >&5
+  ($PKG_CONFIG --exists --print-errors "libzstd") 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; then
+  pkg_cv_ZSTD_CFLAGS=`$PKG_CONFIG --cflags "libzstd" 2>/dev/null`
+		      test "x$?" != "x0" && pkg_failed=yes
+else
+  pkg_failed=yes
+fi
+ else
+    pkg_failed=untried
+fi
+if test -n "$ZSTD_LIBS"; then
+    pkg_cv_ZSTD_LIBS="$ZSTD_LIBS"
+ elif test -n "$PKG_CONFIG"; then
+    if test -n "$PKG_CONFIG" && \
+    { { $as_echo "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libzstd\""; } >&5
+  ($PKG_CONFIG --exists --print-errors "libzstd") 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; then
+  pkg_cv_ZSTD_LIBS=`$PKG_CONFIG --libs "libzstd" 2>/dev/null`
+		      test "x$?" != "x0" && pkg_failed=yes
+else
+  pkg_failed=yes
+fi
+ else
+    pkg_failed=untried
+fi
+
+if test $pkg_failed = no; then
+  pkg_save_LDFLAGS="$LDFLAGS"
+  LDFLAGS="$LDFLAGS $pkg_cv_ZSTD_LIBS"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+
+else
+  pkg_failed=yes
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+  LDFLAGS=$pkg_save_LDFLAGS
+fi
+
+
+
+if test $pkg_failed = yes; then
+        { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
+        _pkg_short_errors_supported=yes
+else
+        _pkg_short_errors_supported=no
+fi
+        if test $_pkg_short_errors_supported = yes; then
+	        ZSTD_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "libzstd" 2>&1`
+        else
+	        ZSTD_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "libzstd" 2>&1`
+        fi
+	# Put the nasty error message in config.log where it belongs
+	echo "$ZSTD_PKG_ERRORS" >&5
+
+
+    if test "$with_zstd" = yes; then
+      as_fn_error $? "--with-zstd was given, but pkgconfig/libzstd.pc is not found" "$LINENO" 5
+    fi
+
+elif test $pkg_failed = untried; then
+        { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+    if test "$with_zstd" = yes; then
+      as_fn_error $? "--with-zstd was given, but pkgconfig/libzstd.pc is not found" "$LINENO" 5
+    fi
+
+else
+	ZSTD_CFLAGS=$pkg_cv_ZSTD_CFLAGS
+	ZSTD_LIBS=$pkg_cv_ZSTD_LIBS
+        { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+
+$as_echo "#define HAVE_ZSTD 1" >>confdefs.h
+
+
+fi
+fi
+
+
 save_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking compiler support for hidden visibility" >&5
diff --git a/bfd/configure.ac b/bfd/configure.ac
index 28f3d1a..7a0ad0f 100644
--- a/bfd/configure.ac
+++ b/bfd/configure.ac
@@ -230,9 +230,10 @@ AC_CHECK_DECLS([basename, ffs, stpcpy, asprintf, vasprintf, strnlen])
 
 BFD_BINARY_FOPEN
 
-# Link in zlib if we can.  This allows us to read compressed debug sections.
+# Link in zlib/zstd if we can.  This allows us to read compressed debug sections.
 # This is used only by compress.c.
 AM_ZLIB
+AC_ZSTD
 
 save_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Werror"
diff --git a/bfd/elf.c b/bfd/elf.c
index 396b56d..d496c1b 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -1260,6 +1260,18 @@ _bfd_elf_make_section_from_shdr (bfd *abfd,
 		 abfd, name);
 	      return false;
 	    }
+#ifndef HAVE_ZSTD
+	  if (newsect->compress_status == DECOMPRESS_SECTION_ZSTD)
+	    {
+	      _bfd_error_handler
+		  /* xgettext:c-format */
+		  (_ ("%pB: section %s is compressed with zstd, but BFD "
+		      "is not built with zstd support"),
+		   abfd, name);
+	      newsect->compress_status = COMPRESS_SECTION_NONE;
+	      return false;
+	    }
+#endif
 	}
 
       if (abfd->is_linker_input)
diff --git a/bfd/elfxx-target.h b/bfd/elfxx-target.h
index feaba84..ca600bb 100644
--- a/bfd/elfxx-target.h
+++ b/bfd/elfxx-target.h
@@ -989,7 +989,8 @@ const bfd_target TARGET_BIG_SYM =
   /* object_flags: mask of all file flags */
   (HAS_RELOC | EXEC_P | HAS_LINENO | HAS_DEBUG | HAS_SYMS | HAS_LOCALS
    | DYNAMIC | WP_TEXT | D_PAGED | BFD_COMPRESS | BFD_DECOMPRESS
-   | BFD_COMPRESS_GABI | BFD_CONVERT_ELF_COMMON | BFD_USE_ELF_STT_COMMON),
+   | BFD_COMPRESS_GABI | BFD_COMPRESS_ZSTD | BFD_CONVERT_ELF_COMMON
+   | BFD_USE_ELF_STT_COMMON),
 
   /* section_flags: mask of all section flags */
   (SEC_HAS_CONTENTS | SEC_ALLOC | SEC_LOAD | SEC_RELOC | SEC_READONLY
@@ -1093,7 +1094,8 @@ const bfd_target TARGET_LITTLE_SYM =
   /* object_flags: mask of all file flags */
   (HAS_RELOC | EXEC_P | HAS_LINENO | HAS_DEBUG | HAS_SYMS | HAS_LOCALS
    | DYNAMIC | WP_TEXT | D_PAGED | BFD_COMPRESS | BFD_DECOMPRESS
-   | BFD_COMPRESS_GABI | BFD_CONVERT_ELF_COMMON | BFD_USE_ELF_STT_COMMON),
+   | BFD_COMPRESS_GABI | BFD_COMPRESS_ZSTD | BFD_CONVERT_ELF_COMMON
+   | BFD_USE_ELF_STT_COMMON),
 
   /* section_flags: mask of all section flags */
   (SEC_HAS_CONTENTS | SEC_ALLOC | SEC_LOAD | SEC_RELOC | SEC_READONLY
diff --git a/bfd/section.c b/bfd/section.c
index c7a02d7..614570e 100644
--- a/bfd/section.c
+++ b/bfd/section.c
@@ -392,7 +392,8 @@ CODE_FRAGMENT
 .  unsigned int compress_status : 2;
 .#define COMPRESS_SECTION_NONE    0
 .#define COMPRESS_SECTION_DONE    1
-.#define DECOMPRESS_SECTION_SIZED 2
+.#define DECOMPRESS_SECTION_ZLIB  2
+.#define DECOMPRESS_SECTION_ZSTD  3
 .
 .  {* The following flags are used by the ELF linker. *}
 .