svn commit: r303114 - head/usr.bin/gcore

[Conrad E. Meyer]

Author: cem
Date: Wed Jul 20 22:03:45 2016
New Revision: 303114
URL: https://svnweb.freebsd.org/changeset/base/303114

Log:
  Add extended segment support to gcore
  
  A follow-up to r303099, D7255.  Basically, apply the exact same change, with
  the exact same rationale, to gcore.  gcore's elfcore.c is largely a clone of
  the kernel imgact_elf coredump facility.
  
  Reviewed by:	emaste (earlier version, not substantially different)
  Requested by:	jhb
  Sponsored by:	EMC / Isilon Storage Division
  Differential Revision:	https://reviews.freebsd.org/D7265

Modified:
  head/usr.bin/gcore/elfcore.c

Modified: head/usr.bin/gcore/elfcore.c
==============================================================================
--- head/usr.bin/gcore/elfcore.c	Wed Jul 20 20:18:52 2016	(r303113)
+++ head/usr.bin/gcore/elfcore.c	Wed Jul 20 22:03:45 2016	(r303114)
@@ -213,6 +213,8 @@ elf_coredump(int efd __unused, int fd, p
 	 */
 	sb = sbuf_new_auto();
 	hdrsize = sizeof(Elf_Ehdr) + sizeof(Elf_Phdr) * (1 + seginfo.count);
+	if (seginfo.count + 1 >= PN_XNUM)
+		hdrsize += sizeof(Elf_Shdr);
 	/* Start header + notes section. */
 	sbuf_start_section(sb, NULL);
 	/* Make empty header subsection. */
@@ -423,10 +425,10 @@ elf_puthdr(pid_t pid, vm_map_entry_t map
 {
 	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;
@@ -446,14 +448,40 @@ elf_puthdr(pid_t pid, vm_map_entry_t map
 	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;
+
+		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;