[binutils-gdb] libctf, bfd: fix ctf_bfdopen_ctfsect opening symbol and string sections

[binutils-gdb] libctf, bfd: fix ctf_bfdopen_ctfsect opening symbol and string sections

[Jose E.Marchesi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=6d5944fca682fe97f37e537f78b665ada2400f51

commit 6d5944fca682fe97f37e537f78b665ada2400f51
Author: Nick Alcock <nick.alcock@oracle.com>
Date:   Thu Jul 11 16:26:54 2019 +0100

    libctf, bfd: fix ctf_bfdopen_ctfsect opening symbol and string sections
    
    The code in ctf_bfdopen_ctfsect (which is the ultimate place where you
    end up if you use ctf_open to open a CTF file and pull in the ELF string
    and symbol tables) was written before it was possible to actually test
    it, since the linker was not written.  Now it is, it turns out that the
    previous code was completely nonfunctional: it assumed that you could
    load the symbol table via bfd_section_from_elf_index (...,elf_onesymtab())
    and the string table via bfd_section_from_elf_index on the sh_link.
    
    Unfortunately BFD loads neither of these sections in the conventional
    fashion it uses for most others: the symbol table is immediately
    converted into internal form (which is useless for our purposes, since
    we also have to work in the absence of BFD for readelf, etc) and the
    string table is loaded specially via bfd_elf_get_str_section which is
    private to bfd/elf.c.
    
    So make this function public, export it in elf-bfd.h, and use it from
    libctf, which does something similar to what bfd_elf_sym_name and
    bfd_elf_string_from_elf_section do.  Similarly, load the symbol table
    manually using bfd_elf_get_elf_syms and throw away the internal form
    it generates for us (we never use it).
    
    BFD allocates the strtab for us via bfd_alloc, so we can leave BFD to
    deallocate it: we allocate the symbol table ourselves before calling
    bfd_elf_get_elf_syms, so we still have to free it.
    
    Also change the rules around what you are allowed to provide: It is
    useful to provide a string section but no symbol table, because CTF
    sections can legitimately have no function info or data object sections
    while relying on the ELF strtab for some of their strings.  So allow
    that combination.
    
    v4: adjust to upstream changes.  ctf_bfdopen_ctfsect's first parameter
        is potentially unused again (if BFD is not in use for this link
        due to not supporting an ELF target).
    v5: fix tabdamage.
    
    bfd/
    	* elf-bfd.h (bfd_elf_get_str_section): Add.
    	* elf.c (bfd_elf_get_str_section): No longer static.
    
    libctf/
    	* ctf-open-bfd.c: Add <assert.h>.
    	(ctf_bfdopen_ctfsect): Open string and symbol tables using
    	techniques borrowed from bfd_elf_sym_name.
    	(ctf_new_archive_internal): Improve comment.
    	* ctf-archive.c (ctf_arc_close): Do not free the ctfi_strsect.
    	* ctf-open.c (ctf_bufopen): Allow opening with a string section but
    	no symbol section, but not vice versa.

Diff:
---
 bfd/ChangeLog         |  5 +++
 bfd/elf-bfd.h         |  1 +
 bfd/elf.c             |  2 +-
 libctf/ChangeLog      | 10 ++++++
 libctf/ctf-archive.c  |  2 +-
 libctf/ctf-open-bfd.c | 98 +++++++++++++++++++++++++++++----------------------
 libctf/ctf-open.c     |  2 +-
 7 files changed, 75 insertions(+), 45 deletions(-)

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 8496cb4..42300c1 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,8 @@
+2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
+
+	* elf-bfd.h (bfd_elf_get_str_section): Add.
+	* elf.c (bfd_elf_get_str_section): No longer static.
+
 2019-09-26  Alan Modra  <amodra@gmail.com>
 
 	PR 24262
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 0a83c17..a9e2d3e 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -2051,6 +2051,7 @@ extern char *bfd_elf_string_from_elf_section
 extern Elf_Internal_Sym *bfd_elf_get_elf_syms
   (bfd *, Elf_Internal_Shdr *, size_t, size_t, Elf_Internal_Sym *, void *,
    Elf_External_Sym_Shndx *);
+extern char * bfd_elf_get_str_section (bfd *, unsigned int);
 extern const char *bfd_elf_sym_name
   (bfd *, Elf_Internal_Shdr *, Elf_Internal_Sym *, asection *);
 
diff --git a/bfd/elf.c b/bfd/elf.c
index 664eae5..bb994b5 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -275,7 +275,7 @@ bfd_elf_mkcorefile (bfd *abfd)
   return elf_tdata (abfd)->core != NULL;
 }
 
-static char *
+char *
 bfd_elf_get_str_section (bfd *abfd, unsigned int shindex)
 {
   Elf_Internal_Shdr **i_shdrp;
diff --git a/libctf/ChangeLog b/libctf/ChangeLog
index d0d0d67..7fa9fc0 100644
--- a/libctf/ChangeLog
+++ b/libctf/ChangeLog
@@ -1,3 +1,13 @@
+2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
+
+	* ctf-open-bfd.c: Add <assert.h>.
+	(ctf_bfdopen_ctfsect): Open string and symbol tables using
+	techniques borrowed from bfd_elf_sym_name.
+	(ctf_new_archive_internal): Improve comment.
+	* ctf-archive.c (ctf_arc_close): Do not free the ctfi_strsect.
+	* ctf-open.c (ctf_bufopen): Allow opening with a string section but
+	no symbol section, but not vice versa.
+
 2019-07-08  Nick Alcock  <nick.alcock@oracle.com>
 
 	* ctf-impl.h (ctf_file_t): New field ctf_openflags.
diff --git a/libctf/ctf-archive.c b/libctf/ctf-archive.c
index 5c16922..a13bac8 100644
--- a/libctf/ctf-archive.c
+++ b/libctf/ctf-archive.c
@@ -405,7 +405,7 @@ ctf_arc_close (ctf_archive_t *arc)
   else
     ctf_file_close (arc->ctfi_file);
   free ((void *) arc->ctfi_symsect.cts_data);
-  free ((void *) arc->ctfi_strsect.cts_data);
+  /* Do not free the ctfi_strsect: it is bound to the bfd.  */
   free (arc->ctfi_data);
   free (arc);
 }
diff --git a/libctf/ctf-open-bfd.c b/libctf/ctf-open-bfd.c
index 6a0c155..6fbbde8 100644
--- a/libctf/ctf-open-bfd.c
+++ b/libctf/ctf-open-bfd.c
@@ -19,6 +19,7 @@
 
 #include <ctf-impl.h>
 #include <stddef.h>
+#include <assert.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <errno.h>
@@ -32,8 +33,9 @@
 #include "elf-bfd.h"
 
 /* Make a new struct ctf_archive_internal wrapper for a ctf_archive or a
-   ctf_file.  Closes ARC and/or FP on error.  Arrange to free the SYMSECT and
-   STRSECT interior on close.  */
+   ctf_file.  Closes ARC and/or FP on error.  Arrange to free the SYMSECT or
+   STRSECT, as needed, on close (though the STRSECT interior is bound to the bfd
+   * and is not actually freed by this machinery).  */
 
 static struct ctf_archive_internal *
 ctf_new_archive_internal (int is_archive, struct ctf_archive *arc,
@@ -130,50 +132,63 @@ ctf_bfdopen_ctfsect (struct bfd *abfd _libctf_unused_,
   int is_archive;
 
 #ifdef HAVE_BFD_ELF
-  asection *sym_asect;
   ctf_sect_t symsect, strsect;
+  Elf_Internal_Shdr *strhdr;
+  Elf_Internal_Shdr *symhdr = &elf_symtab_hdr (abfd);
+  size_t symcount = symhdr->sh_size / symhdr->sh_entsize;
+  Elf_Internal_Sym *isymbuf;
+  bfd_byte *symtab;
+  const char *strtab = NULL;
   /* TODO: handle SYMTAB_SHNDX.  */
 
-  if ((sym_asect = bfd_section_from_elf_index (abfd,
-					       elf_onesymtab (abfd))) != NULL)
+  if ((symtab = malloc (symhdr->sh_size)) == NULL)
     {
-      Elf_Internal_Shdr *symhdr = &elf_symtab_hdr (abfd);
-      asection *str_asect = NULL;
-      bfd_byte *contents;
-
-      if (symhdr->sh_link != SHN_UNDEF &&
-	  symhdr->sh_link <= elf_numsections (abfd))
-	str_asect = bfd_section_from_elf_index (abfd, symhdr->sh_link);
+      bfderrstr = "Cannot malloc symbol table";
+      goto err;
+    }
 
-      Elf_Internal_Shdr *strhdr = elf_elfsections (abfd)[symhdr->sh_link];
+  isymbuf = bfd_elf_get_elf_syms (abfd, symhdr, symcount, 0,
+				  NULL, symtab, NULL);
+  free (isymbuf);
+  if (isymbuf == NULL)
+    {
+      bfderrstr = "Cannot read symbol table";
+      goto err_free_sym;
+    }
 
-      if (sym_asect && str_asect)
+  if (elf_elfsections (abfd) != NULL
+      && symhdr->sh_link < elf_numsections (abfd))
+    {
+      strhdr = elf_elfsections (abfd)[symhdr->sh_link];
+      if (strhdr->contents == NULL)
 	{
-	  if (!bfd_malloc_and_get_section (abfd, str_asect, &contents))
-	    {
-	      bfderrstr = "Cannot malloc string table";
-	      free (contents);
-	      goto err;
-	    }
-	  strsect.cts_data = contents;
-	  strsect.cts_name = (char *) strsect.cts_data + strhdr->sh_name;
-	  strsect.cts_size = bfd_section_size (str_asect);
-	  strsect.cts_entsize = strhdr->sh_size;
-	  strsectp = &strsect;
-
-	  if (!bfd_malloc_and_get_section (abfd, sym_asect, &contents))
+	  if ((strtab = bfd_elf_get_str_section (abfd, symhdr->sh_link)) == NULL)
 	    {
-	      bfderrstr = "Cannot malloc symbol table";
-	      free (contents);
-	      goto err_free_str;
+	      bfderrstr = "Cannot read string table";
+	      goto err_free_sym;
 	    }
-
-	  symsect.cts_name = (char *) strsect.cts_data + symhdr->sh_name;
-	  symsect.cts_entsize = symhdr->sh_size;
-	  symsect.cts_size = bfd_section_size (sym_asect);
-	  symsect.cts_data = contents;
-	  symsectp = &symsect;
 	}
+      else
+	strtab = (const char *) strhdr->contents;
+    }
+
+  if (strtab)
+    {
+      /* The names here are more or less arbitrary, but there is no point
+	 thrashing around digging the name out of the shstrtab given that we don't
+	 use it for anything but debugging.  */
+
+      strsect.cts_data = strtab;
+      strsect.cts_name = ".strtab";
+      strsect.cts_size = strhdr->sh_size;
+      strsectp = &strsect;
+
+      assert (symhdr->sh_entsize == get_elf_backend_data (abfd)->s->sizeof_sym);
+      symsect.cts_name = ".symtab";
+      symsect.cts_entsize = symhdr->sh_entsize;
+      symsect.cts_size = symhdr->sh_size;
+      symsect.cts_data = symtab;
+      symsectp = &symsect;
     }
 #endif
 
@@ -183,7 +198,7 @@ ctf_bfdopen_ctfsect (struct bfd *abfd _libctf_unused_,
       is_archive = 1;
       if ((arc = ctf_arc_bufopen ((void *) ctfsect->cts_data,
 				  ctfsect->cts_size, errp)) == NULL)
-	goto err_free_sym;
+	goto err_free_str;
     }
   else
     {
@@ -192,7 +207,7 @@ ctf_bfdopen_ctfsect (struct bfd *abfd _libctf_unused_,
 	{
 	  ctf_dprintf ("ctf_internal_open(): cannot open CTF: %s\n",
 		       ctf_errmsg (*errp));
-	  goto err_free_sym;
+	  goto err_free_str;
 	}
     }
   arci = ctf_new_archive_internal (is_archive, arc, fp, symsectp, strsectp,
@@ -200,11 +215,10 @@ ctf_bfdopen_ctfsect (struct bfd *abfd _libctf_unused_,
 
   if (arci)
     return arci;
- err_free_sym:
+ err_free_str: ;
 #ifdef HAVE_BFD_ELF
-  free ((void *) symsect.cts_data);
-err_free_str:
-  free ((void *) strsect.cts_data);
+ err_free_sym:
+  free (symtab);
 #endif
 err: _libctf_unused_;
   if (bfderrstr)
diff --git a/libctf/ctf-open.c b/libctf/ctf-open.c
index 2979ef8..51f9edc 100644
--- a/libctf/ctf-open.c
+++ b/libctf/ctf-open.c
@@ -1244,7 +1244,7 @@ ctf_bufopen (const ctf_sect_t *ctfsect, const ctf_sect_t *symsect,
 
   libctf_init_debug();
 
-  if (ctfsect == NULL || ((symsect == NULL) != (strsect == NULL)))
+  if ((ctfsect == NULL) || ((symsect != NULL) && (strsect == NULL)))
     return (ctf_set_open_errno (errp, EINVAL));
 
   if (symsect != NULL && symsect->cts_entsize != sizeof (Elf32_Sym) &&