libelf: add compression header support

GNU and Oracle libelf implementations added support for section
compression, intended to reduce the size of DWARF debug info (which
might be an order of magnitude larger than the code).

There are two compressed ELF section formats:

1. Old GNU - sections are renmaed to start with 'z'.  Section contains
   a magic number, uncompressed size, and compressed data.

2. Oracle and New GNU - compressed sections use the SHF_COMPRESSED flag.
   The compression header contains the compression type, uncompressed
   size, and uncompressed alignment.

The second style is preferred and this change implements only that one.

Submitted by:	Tiger Gao <tig@FreeBSDFoundation.org>
Reviewed by:	markj
MFC after:	2 weeks
Relnotes:	Yes
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D24566

contrib/elftoolchain/libelf/Version.map

@@ -91,6 +91,13 @@ global:
 	gelf_update_symshndx;
 	gelf_xlatetof;
 	gelf_xlatetom;
+};
+
+R1.1 {
+global:
+	elf32_getchdr;
+	elf64_getchdr;
+	gelf_getchdr;
 local:
 	*;
-};
+} R1.0;

contrib/elftoolchain/libelf/_libelf.h

@@ -220,6 +220,7 @@ size_t	_libelf_fsize(Elf_Type _t, int _elfclass, unsigned int _version,
     size_t count);
 _libelf_translator_function *_libelf_get_translator(Elf_Type _t,
     int _direction, int _elfclass, int _elfmachine);
+void	*_libelf_getchdr(Elf_Scn *_e, int _elfclass);
 void	*_libelf_getphdr(Elf *_e, int _elfclass);
 void	*_libelf_getshdr(Elf_Scn *_scn, int _elfclass);
 void	_libelf_init_elf(Elf *_e, Elf_Kind _kind);

contrib/elftoolchain/libelf/gelf.3

@@ -23,7 +23,7 @@
 .\"
 .\" $Id: gelf.3 3743 2019-06-12 19:36:30Z jkoshy $
 .\"
-.Dd June 12, 2019
+.Dd October 23, 2020
 .Dt GELF 3
 .Os
 .Sh NAME
@@ -45,6 +45,8 @@ The GElf API defines the following class-independent data structures:
 .Bl -tag -width GElf_Sxword
 .It Vt GElf_Addr
 A representation of ELF addresses.
+.It Vt GElf_Chdr
+A class-independent representation of an ELF Compression Header.
 .It Vt GElf_Dyn
 A class-independent representation of ELF
 .Sy .dynamic
@@ -144,6 +146,8 @@ native representation.
 .El
 .It "Retrieving ELF Data"
 .Bl -tag -compact -width indent
+.It Fn gelf_getchdr
+Retrieve an ELF Compression Header from the underlying ELF descriptor.
 .It Fn gelf_getdyn
 Retrieve an ELF
 .Sy .dynamic

contrib/elftoolchain/libelf/gelf.h

@@ -39,6 +39,7 @@ typedef Elf64_Sxword	GElf_Sxword;	/* Signed long words (64 bit) */
 typedef Elf64_Word	GElf_Word;	/* Unsigned words (32 bit) */
 typedef Elf64_Xword	GElf_Xword;	/* Unsigned long words (64 bit) */
 
+typedef Elf64_Chdr	GElf_Chdr;	/* Compressed section header */
 typedef Elf64_Dyn	GElf_Dyn;	/* ".dynamic" section entries */
 typedef Elf64_Ehdr	GElf_Ehdr;	/* ELF header */
 typedef Elf64_Phdr	GElf_Phdr;	/* Program header */
@@ -73,6 +74,7 @@ extern "C" {
 long		gelf_checksum(Elf *_elf);
 size_t		gelf_fsize(Elf *_elf, Elf_Type _type, size_t _count,
 			unsigned int _version);
+GElf_Chdr	*gelf_getchdr(Elf_Scn *_scn, GElf_Chdr *_dst);
 int		gelf_getclass(Elf *_elf);
 GElf_Dyn	*gelf_getdyn(Elf_Data *_data, int _index, GElf_Dyn *_dst);
 GElf_Ehdr	*gelf_getehdr(Elf *_elf, GElf_Ehdr *_dst);

contrib/elftoolchain/libelf/gelf_chdr.c

@@ -0,0 +1,82 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2020 The FreeBSD Foundation
+ *
+ * This software was developed by Tiger Gao under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <gelf.h>
+#include <libelf.h>
+#include <limits.h>
+#include <stdint.h>
+
+#include "_libelf.h"
+
+Elf32_Chdr *
+elf32_getchdr(Elf_Scn *s)
+{
+	return (_libelf_getchdr(s, ELFCLASS32));
+}
+
+Elf64_Chdr *
+elf64_getchdr(Elf_Scn *s)
+{
+	return (_libelf_getchdr(s, ELFCLASS64));
+}
+
+GElf_Chdr *
+gelf_getchdr(Elf_Scn *s, GElf_Chdr *d)
+{
+	int ec;
+	void *ch;
+	Elf32_Chdr *ch32;
+	Elf64_Chdr *ch64;
+
+	if (d == NULL) {
+		LIBELF_SET_ERROR(ARGUMENT, 0);
+		return (NULL);
+	}
+
+	if ((ch = _libelf_getchdr(s, ELFCLASSNONE)) == NULL)
+		return (NULL);
+
+	ec = s->s_elf->e_class;
+	assert(ec == ELFCLASS32 || ec == ELFCLASS64);
+
+	if (ec == ELFCLASS32) {
+		ch32 = (Elf32_Chdr *)ch;
+
+		d->ch_type = (Elf64_Word)ch32->ch_type;
+		d->ch_size = (Elf64_Xword)ch32->ch_size;
+		d->ch_addralign = (Elf64_Xword)ch32->ch_addralign;
+	} else {
+		ch64 = (Elf64_Chdr *)ch;
+		*d = *ch64;
+	}
+
+	return (d);
+}

contrib/elftoolchain/libelf/gelf_getchdr.3

@@ -0,0 +1,117 @@
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (c) 2020 The FreeBSD Foundation
+.\"
+.\" This document was written by Tiger Gao under sponsorship from
+.\" the FreeBSD Foundation.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions are
+.\" met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $Id: gelf_getchdr.3 3639 2020-10-20 16:07:02Z tig $
+.\"
+.Dd October 23, 2020
+.Dt GELF_GETCHDR 3
+.Os
+.Sh NAME
+.Nm elf32_getchdr ,
+.Nm elf64_getchdr ,
+.Nm gelf_getchdr
+.Nd retrieve the compression header of a section
+.Sh LIBRARY
+.Lb libelf
+.Sh SYNOPSIS
+.In libelf.h
+.Ft "Elf32_Chdr *"
+.Fn elf32_getchdr "Elf_Scn *s"
+.Ft "Elf64_Chdr *"
+.Fn elf64_getchdr "Elf_Scn *s"
+.In gelf.h
+.Ft "GElf_Chdr *"
+.Fn gelf_getchdr "Elf_Scn *scn" "GElf_Chdr *chdr"
+.Sh DESCRIPTION
+These functions return a pointer to the ELF Compression Header data
+structure associated with section descriptor
+.Ar scn .
+.Pp
+Function
+.Fn elf32_getchdr
+retrieves a pointer to an
+.Vt Elf32_Chdr
+structure.
+Section descriptor
+.Ar scn
+must be associated with an ELF descriptor of class
+.Dv ELFCLASS32 .
+.Pp
+Function
+.Fn elf64_getchdr
+retrieves a pointer to an
+.Vt Elf64_Chdr
+structure.
+Section descriptor
+.Ar scn
+must be associated with an ELF descriptor of class
+.Dv ELFCLASS64 .
+.Pp
+Function
+.Fn gelf_getchdr
+copies the values in the compression header associated with argument
+.Ar scn
+to the structure pointed to be argument
+.Ar dst .
+The
+.Vt GElf_Chdr
+data structure is described in
+.Xr gelf 3 .
+.Sh RETURN VALUES
+Functions
+.Fn elf32_getchdr
+and
+.Fn elf64_getchdr
+return a valid pointer to the appropriate compression header on success
+or NULL if an error was encountered.
+.Pp
+Function
+.Fn gelf_getchdr
+returns argument
+.Ar dst
+if successful, or NULL if an error was encountered.
+.Sh ERRORS
+These functions may fail with the following errors:
+.Bl -tag -width "[ELF_E_RESOURCE]"
+.It Bq Er ELF_E_INVALID_SECTION_FLAGS
+Arguments
+.Ar scn
+has invalid flags.
+.It Bq Er ELF_E_INVALID_SECTION_TYPE
+Argument
+.Ar scn
+has invalid type.
+.It Bq Er ELF_E_NOT_COMPRESSED
+Argument
+.Ar scn
+is not compressed.
+.El
+.Sh SEE ALSO
+.Xr elf 3 ,
+.Xr elf_getscn 3 ,
+.Xr gelf 3 ,

contrib/elftoolchain/libelf/libelf.h

@@ -162,6 +162,9 @@ enum Elf_Error {
 	ELF_E_SEQUENCE,	/* API calls out of sequence */
 	ELF_E_UNIMPL,	/* Feature is unimplemented */
 	ELF_E_VERSION,	/* Unknown API version */
+	ELF_E_INVALID_SECTION_FLAGS, /* Invalid ELF section header flags */
+	ELF_E_INVALID_SECTION_TYPE, /* Invalid ELF section header type */
+	ELF_E_NOT_COMPRESSED, /* Section is not compressed */
 	ELF_E_NUM	/* Max error number */
 };
 
@@ -227,6 +230,7 @@ unsigned int	elf_version(unsigned int _version);
 long		elf32_checksum(Elf *_elf);
 size_t		elf32_fsize(Elf_Type _type, size_t _count,
 			unsigned int _version);
+Elf32_Chdr	*elf32_getchdr(Elf_Scn *_scn);
 Elf32_Ehdr	*elf32_getehdr(Elf *_elf);
 Elf32_Phdr	*elf32_getphdr(Elf *_elf);
 Elf32_Shdr	*elf32_getshdr(Elf_Scn *_scn);
@@ -240,6 +244,7 @@ Elf_Data	*elf32_xlatetom(Elf_Data *_dst, const Elf_Data *_src,
 long		elf64_checksum(Elf *_elf);
 size_t		elf64_fsize(Elf_Type _type, size_t _count,
 			unsigned int _version);
+Elf64_Chdr	*elf64_getchdr(Elf_Scn *_scn);
 Elf64_Ehdr	*elf64_getehdr(Elf *_elf);
 Elf64_Phdr	*elf64_getphdr(Elf *_elf);
 Elf64_Shdr	*elf64_getshdr(Elf_Scn *_scn);

contrib/elftoolchain/libelf/libelf_chdr.c

@@ -0,0 +1,104 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2020 The FreeBSD Foundation
+ *
+ * This software was developed by Tiger Gao under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <gelf.h>
+#include <libelf.h>
+
+#include "_libelf.h"
+
+void *
+_libelf_getchdr(Elf_Scn *s, int ec)
+{
+	Elf *e;
+	void *sh;
+	Elf32_Shdr *sh32;
+	Elf64_Shdr *sh64;
+
+	sh32 = NULL;
+	sh64 = NULL;
+
+	if (s == NULL || (e = s->s_elf) == NULL || e->e_kind != ELF_K_ELF) {
+		LIBELF_SET_ERROR(ARGUMENT, 0);
+		return (NULL);
+	}
+
+	if (ec == ELFCLASSNONE) {
+		ec = e->e_class;
+	} else if (ec != e->e_class) {
+		LIBELF_SET_ERROR(CLASS, 0);
+		return (NULL);
+	}
+
+	if ((sh = _libelf_getshdr(s, ec)) == NULL) {
+		LIBELF_SET_ERROR(HEADER, 0);
+		return (NULL);
+	}
+
+	if (ec == ELFCLASS32) {
+		sh32 = (Elf32_Shdr *)sh;
+		if ((sh32->sh_flags & SHF_ALLOC) != 0) {
+			LIBELF_SET_ERROR(INVALID_SECTION_FLAGS, 0);
+			return (NULL);
+		}
+
+		if (sh32->sh_type == SHT_NULL || sh32->sh_type == SHT_NOBITS) {
+			LIBELF_SET_ERROR(INVALID_SECTION_TYPE, 0);
+			return (NULL);
+		}
+
+		if ((sh32->sh_flags & SHF_COMPRESSED) == 0) {
+			LIBELF_SET_ERROR(NOT_COMPRESSED, 0);
+			return (NULL);
+		}
+	} else {
+		sh64 = (Elf64_Shdr *)sh;
+		if ((sh64->sh_flags & SHF_ALLOC) != 0) {
+			LIBELF_SET_ERROR(INVALID_SECTION_FLAGS, 0);
+			return (NULL);
+		}
+
+		if (sh64->sh_type == SHT_NULL || sh64->sh_type == SHT_NOBITS) {
+			LIBELF_SET_ERROR(INVALID_SECTION_TYPE, 0);
+			return (NULL);
+		}
+
+		if ((sh64->sh_flags & SHF_COMPRESSED) == 0) {
+			LIBELF_SET_ERROR(NOT_COMPRESSED, 0);
+			return (NULL);
+		}
+	}
+
+	Elf_Data *d = elf_getdata(s, NULL);
+
+	if (!d)
+		return (NULL);
+
+	return ((void *)d->d_buf);
+}

lib/libelf/Makefile

@@ -38,6 +38,7 @@ SRCS=	elf.c							\
 	elf_update.c						\
 	elf_version.c						\
 	gelf_cap.c						\
+	gelf_chdr.c						\
 	gelf_checksum.c						\
 	gelf_dyn.c						\
 	gelf_ehdr.c						\
@@ -57,6 +58,7 @@ SRCS=	elf.c							\
 	libelf_allocate.c					\
 	libelf_ar.c						\
 	libelf_ar_util.c					\
+	libelf_chdr.c						\
 	libelf_checksum.c					\
 	libelf_data.c						\
 	libelf_ehdr.c						\