strip: Add --keep-section=SECTION and --remove-section=SECTION.

Adds two new output options:

  --keep-section=SECTION Keep the named section.  SECTION is an extended
                         wildcard pattern.  May be given more than once.

  --remove-section=SECTION   Remove the named section.  SECTION is an
                         extended wildcard pattern.  May be given more than
                         once.  Only non-allocated sections can be removed.

The --remove-section was already partially implemented, but only for the
.comment section. The short option -R is to be compatible with binutils.

The new testcase makes sure that various combinations of kept/removed
sections pull the correct dependencies into the output and/or debug files.

https://bugzilla.redhat.com/show_bug.cgi?id=1465997

Signed-off-by: Mark Wielaard <[email protected]>

1 files changed, 110 insertions, 17 deletions

diff --git a/src/strip.c b/src/strip.c
index 2bf95f90..4a35ea1d 100644
--- a/src/strip.c
+++ b/src/strip.c
@@ -26,6 +26,7 @@
 #include <endian.h>
 #include <error.h>
 #include <fcntl.h>
+#include <fnmatch.h>
 #include <gelf.h>
 #include <libelf.h>
 #include <libintl.h>
@@ -60,6 +61,7 @@ ARGP_PROGRAM_BUG_ADDRESS_DEF = PACKAGE_BUGREPORT;
 #define OPT_PERMISSIVE		0x101
 #define OPT_STRIP_SECTIONS	0x102
 #define OPT_RELOC_DEBUG 	0x103
+#define OPT_KEEP_SECTION 	0x104
 
 
 /* Definitions of arguments for argp functions.  */
@@ -83,7 +85,8 @@ static const struct argp_option options[] =
     N_("Resolve all trivial relocations between debug sections if the removed sections are placed in a debug file (only relevant for ET_REL files, operation is not reversable, needs -f)"), 0 },
   { "remove-comment", OPT_REMOVE_COMMENT, NULL, 0,
     N_("Remove .comment section"), 0 },
-  { "remove-section", 'R', "SECTION", OPTION_HIDDEN, NULL, 0 },
+  { "remove-section", 'R', "SECTION", 0, N_("Remove the named section.  SECTION is an extended wildcard pattern.  May be given more than once.  Only non-allocated sections can be removed."), 0 },
+  { "keep-section", OPT_KEEP_SECTION, "SECTION", 0, N_("Keep the named section.  SECTION is an extended wildcard pattern.  May be given more than once."), 0 },
   { "permissive", OPT_PERMISSIVE, NULL, 0,
     N_("Relax a few rules to handle slightly broken ELF files"), 0 },
   { NULL, 0, NULL, 0, NULL, 0 }
@@ -157,6 +160,58 @@ static bool permissive;
 /* If true perform relocations between debug sections.  */
 static bool reloc_debug;
 
+/* Sections the user explicitly wants to keep or remove.  */
+struct section_pattern
+{
+  char *pattern;
+  struct section_pattern *next;
+};
+
+static struct section_pattern *keep_secs = NULL;
+static struct section_pattern *remove_secs = NULL;
+
+static void
+add_pattern (struct section_pattern **patterns, const char *pattern)
+{
+  struct section_pattern *p = xmalloc (sizeof *p);
+  p->pattern = xstrdup (pattern);
+  p->next = *patterns;
+  *patterns = p;
+}
+
+static void
+free_sec_patterns (struct section_pattern *patterns)
+{
+  struct section_pattern *pattern = patterns;
+  while (pattern != NULL)
+    {
+      struct section_pattern *p = pattern;
+      pattern = p->next;
+      free (p->pattern);
+      free (p);
+    }
+}
+
+static void
+free_patterns (void)
+{
+  free_sec_patterns (keep_secs);
+  free_sec_patterns (remove_secs);
+}
+
+static bool
+section_name_matches (struct section_pattern *patterns, const char *name)
+{
+  struct section_pattern *pattern = patterns;
+  while (pattern != NULL)
+    {
+      if (fnmatch (pattern->pattern, name, FNM_EXTMATCH) == 0)
+	return true;
+      pattern = pattern->next;
+    }
+  return false;
+}
+
 
 int
 main (int argc, char *argv[])
@@ -207,6 +262,7 @@ Only one input file allowed together with '-o' and '-f'"));
       while (++remaining < argc);
     }
 
+  free_patterns ();
   return result;
 }
 
@@ -257,14 +313,13 @@ parse_opt (int key, char *arg, struct argp_state *state)
       break;
 
     case 'R':
-      if (!strcmp (arg, ".comment"))
+      if (fnmatch (arg, ".comment", FNM_EXTMATCH) == 0)
 	remove_comment = true;
-      else
-	{
-	  argp_error (state,
-		      gettext ("-R option supports only .comment section"));
-	  return EINVAL;
-	}
+      add_pattern (&remove_secs, arg);
+      break;
+
+    case OPT_KEEP_SECTION:
+      add_pattern (&keep_secs, arg);
       break;
 
     case 'g':
@@ -284,6 +339,16 @@ parse_opt (int key, char *arg, struct argp_state *state)
     case 's':			/* Ignored for compatibility.  */
       break;
 
+    case ARGP_KEY_SUCCESS:
+      if (remove_comment == true
+	  && section_name_matches (keep_secs, ".comment"))
+	{
+	  argp_error (state,
+		      gettext ("cannot both keep and remove .comment section"));
+	  return EINVAL;
+	}
+      break;
+
     default:
       return ARGP_ERR_UNKNOWN;
     }
@@ -622,6 +687,28 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 	  goto fail_close;
 	}
 
+      /* Sanity check the user.  */
+      if (section_name_matches (remove_secs, shdr_info[cnt].name))
+	{
+	  if ((shdr_info[cnt].shdr.sh_flags & SHF_ALLOC) != 0)
+	    {
+	      error (0, 0,
+		     gettext ("Cannot remove allocated section '%s'"),
+		     shdr_info[cnt].name);
+	      result = 1;
+	      goto fail_close;
+	    }
+
+	  if (section_name_matches (keep_secs, shdr_info[cnt].name))
+	    {
+	      error (0, 0,
+		     gettext ("Cannot both keep and remove section '%s'"),
+		     shdr_info[cnt].name);
+	      result = 1;
+	      goto fail_close;
+	    }
+	}
+
       /* Mark them as present but not yet investigated.  */
       shdr_info[cnt].idx = 1;
 
@@ -709,6 +796,7 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
        know how to handle them
      - if a section is referred to from a section which is not removed
        in the sh_link or sh_info element it cannot be removed either
+     - the user might have explicitly said to remove or keep a section
   */
   for (cnt = 1; cnt < shnum; ++cnt)
     /* Check whether the section can be removed.  Since we will create
@@ -717,8 +805,13 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 	: (ebl_section_strip_p (ebl, ehdr, &shdr_info[cnt].shdr,
 				shdr_info[cnt].name, remove_comment,
 				remove_debug)
-	   || cnt == ehdr->e_shstrndx))
+	   || cnt == ehdr->e_shstrndx
+	   || section_name_matches (remove_secs, shdr_info[cnt].name)))
       {
+	/* The user might want to explicitly keep this one.  */
+	if (section_name_matches (keep_secs, shdr_info[cnt].name))
+	  continue;
+
 	/* For now assume this section will be removed.  */
 	shdr_info[cnt].idx = 0;
 
@@ -2174,14 +2267,14 @@ while computing checksum for debug information"));
   if (shdr_info != NULL)
     {
       /* For some sections we might have created an table to map symbol
-	 table indices.  */
-      if (any_symtab_changes)
-	for (cnt = 1; cnt <= shdridx; ++cnt)
-	  {
-	    free (shdr_info[cnt].newsymidx);
-	    if (shdr_info[cnt].debug_data != NULL)
-	      free (shdr_info[cnt].debug_data->d_buf);
-	  }
+	 table indices.  Or we might kept (original) data around to put
+	 into the .debug file.  */
+      for (cnt = 1; cnt <= shdridx; ++cnt)
+	{
+	  free (shdr_info[cnt].newsymidx);
+	  if (shdr_info[cnt].debug_data != NULL)
+	    free (shdr_info[cnt].debug_data->d_buf);
+	}
 
       /* Free data we allocated for the .gnu_debuglink section. */
       free (debuglink_buf);