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Date:      Wed, 20 Jul 2016 16:59:36 +0000 (UTC)
From:      "Conrad E. Meyer" <cem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r303099 - head/sys/kern
Message-ID:  <201607201659.u6KGxaNs010929@repo.freebsd.org>
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Author: cem
Date: Wed Jul 20 16:59:36 2016
New Revision: 303099
URL: https://svnweb.freebsd.org/changeset/base/303099

Log:
  Extend ELF coredump to support more than 65535 segments
  
  The ELF e_phnum field is only 16 bits wide. To support more than 65535 segments
  (program headers), Sun's "Linker and Libraries Guide" table 7-7 (or 12-7,
  depending on document version) prescribes a special first section header where
  sh_info represents the real number of program headers.
  
  Test code to follow, when it is ready.
  
  Reference:	http://docs.oracle.com/cd/E18752_01/pdf/817-1984.pdf
  
  Reviewed by:	emaste, markj
  Sponsored by:	EMC / Isilon Storage Division
  Differential Revision:	https://reviews.freebsd.org/D7255

Modified:
  head/sys/kern/imgact_elf.c

Modified: head/sys/kern/imgact_elf.c
==============================================================================
--- head/sys/kern/imgact_elf.c	Wed Jul 20 16:48:25 2016	(r303098)
+++ head/sys/kern/imgact_elf.c	Wed Jul 20 16:59:36 2016	(r303099)
@@ -1323,6 +1323,8 @@ __elfN(coredump)(struct thread *td, stru
 	 * Collect info about the core file header area.
 	 */
 	hdrsize = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * (1 + seginfo.count);
+	if (seginfo.count + 1 >= PN_XNUM)
+		hdrsize += sizeof(Elf_Shdr);
 	__elfN(prepare_notes)(td, &notelst, &notesz);
 	coresize = round_page(hdrsize + notesz) + seginfo.size;
 
@@ -1618,10 +1620,10 @@ __elfN(puthdr)(struct thread *td, void *
 {
 	Elf_Ehdr *ehdr;
 	Elf_Phdr *phdr;
+	Elf_Shdr *shdr;
 	struct phdr_closure phc;
 
 	ehdr = (Elf_Ehdr *)hdr;
-	phdr = (Elf_Phdr *)((char *)hdr + sizeof(Elf_Ehdr));
 
 	ehdr->e_ident[EI_MAG0] = ELFMAG0;
 	ehdr->e_ident[EI_MAG1] = ELFMAG1;
@@ -1645,14 +1647,43 @@ __elfN(puthdr)(struct thread *td, void *
 	ehdr->e_flags = 0;
 	ehdr->e_ehsize = sizeof(Elf_Ehdr);
 	ehdr->e_phentsize = sizeof(Elf_Phdr);
-	ehdr->e_phnum = numsegs + 1;
 	ehdr->e_shentsize = sizeof(Elf_Shdr);
-	ehdr->e_shnum = 0;
 	ehdr->e_shstrndx = SHN_UNDEF;
+	if (numsegs + 1 < PN_XNUM) {
+		ehdr->e_phnum = numsegs + 1;
+		ehdr->e_shnum = 0;
+	} else {
+		ehdr->e_phnum = PN_XNUM;
+		ehdr->e_shnum = 1;
+
+		ehdr->e_shoff = ehdr->e_phoff +
+		    (numsegs + 1) * ehdr->e_phentsize;
+		KASSERT(ehdr->e_shoff == hdrsize - sizeof(Elf_Shdr),
+		    ("e_shoff: %zu, hdrsize - shdr: %zu",
+		     ehdr->e_shoff, hdrsize - sizeof(Elf_Shdr)));
+
+		shdr = (Elf_Shdr *)((char *)hdr + ehdr->e_shoff);
+		memset(shdr, 0, sizeof(*shdr));
+		/*
+		 * A special first section is used to hold large segment and
+		 * section counts.  This was proposed by Sun Microsystems in
+		 * Solaris and has been adopted by Linux; the standard ELF
+		 * tools are already familiar with the technique.
+		 *
+		 * See table 7-7 of the Solaris "Linker and Libraries Guide"
+		 * (or 12-7 depending on the version of the document) for more
+		 * details.
+		 */
+		shdr->sh_type = SHT_NULL;
+		shdr->sh_size = ehdr->e_shnum;
+		shdr->sh_link = ehdr->e_shstrndx;
+		shdr->sh_info = numsegs + 1;
+	}
 
 	/*
 	 * Fill in the program header entries.
 	 */
+	phdr = (Elf_Phdr *)((char *)hdr + ehdr->e_phoff);
 
 	/* The note segement. */
 	phdr->p_type = PT_NOTE;

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