Handle VDSO section headers past end of page

When a VDSO gets large enough that it doesn't entirely fit in one page,
but not so large that the part described by the program header exceeds
one page, then gdb/BFD doesn't read the section headers and symbol
table information.  This patch cures that by passing the size of the
vdso to BFD, and fixes a number of other issues in the BFD code.

bfd/
	* elfcode.h (bfd_from_remote_memory): Add "size" parameter.
	Consolidate code handling possible section headers past end of
	segment.  Don't use p_align for page size guess, instead use
	minpagesize.  Take note of ld.so clearing section headers when
	p_memsz > p_filesz.  Handle file header specifying no section
	headers.  Handle zero p_align throughout.  Default loadbase to
	zero.  Add comments.  Rename contents_size to high_offset, and
	make it a bfd_vma.  Delete unnecessary bfd_set_error calls.
	* bfd-in.h (bfd_elf_bfd_from_remote_memory): Update prototpe.
	* elf-bfd.h (struct elf_backend_data <elf_backend_from_remote_memory>):
	Likewise.
	(_bfd_elf32_bfd_from_remote_memory): Likewise.
	(_bfd_elf64_bfd_from_remote_memory): Likewise.
	* elf.c (bfd_elf_bfd_from_remote_memory): Adjust.
	* bfd-in2.h: Regnerate.
gdb/
	* symfile-mem.c (symbol_file_add_from_memory): Add size parameter.
	Pass to bfd_elf_bfd_from_remote_memory.  Adjust all callers.
	(struct symbol_file_add_from_memory_args): Add size field.
	(find_vdso_size): New function.
	(add_vsyscall_page): Attempt to find vdso size.

1 files changed, 31 insertions, 7 deletions

diff --git a/gdb/symfile-mem.c b/gdb/symfile-mem.c
index e3230de..3f09c4d 100644
--- a/gdb/symfile-mem.c
+++ b/gdb/symfile-mem.c
@@ -76,13 +76,14 @@ target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
 }
 
 /* Read inferior memory at ADDR to find the header of a loaded object file
-   and read its in-core symbols out of inferior memory.  TEMPL is a bfd
+   and read its in-core symbols out of inferior memory.  SIZE, if
+   non-zero, is the known size of the object.  TEMPL is a bfd
    representing the target's format.  NAME is the name to use for this
    symbol file in messages; it can be NULL or a malloc-allocated string
    which will be attached to the BFD.  */
 static struct objfile *
-symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
-			     int from_tty)
+symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr,
+			     size_t size, char *name, int from_tty)
 {
   struct objfile *objf;
   struct bfd *nbfd;
@@ -95,7 +96,7 @@ symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
     error (_("add-symbol-file-from-memory not supported for this target"));
 
-  nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
+  nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
 					 target_read_memory_bfd);
   if (nbfd == NULL)
     error (_("Failed to read a valid object file image from memory."));
@@ -158,7 +159,7 @@ add_symbol_file_from_memory_command (char *args, int from_tty)
     error (_("Must use symbol-file or exec-file "
 	     "before add-symbol-file-from-memory."));
 
-  symbol_file_add_from_memory (templ, addr, NULL, from_tty);
+  symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 }
 
 /* Arguments for symbol_file_add_from_memory_wrapper.  */
@@ -167,6 +168,7 @@ struct symbol_file_add_from_memory_args
 {
   struct bfd *bfd;
   CORE_ADDR sysinfo_ehdr;
+  size_t size;
   char *name;
   int from_tty;
 };
@@ -179,8 +181,25 @@ symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 {
   struct symbol_file_add_from_memory_args *args = data;
 
-  symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
-			       args->from_tty);
+  symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->size,
+			       args->name, args->from_tty);
+  return 0;
+}
+
+/* Rummage through mappings to find the vsyscall page size.  */
+
+static int
+find_vdso_size (CORE_ADDR vaddr, unsigned long size,
+		int read, int write, int exec, int modified,
+		void *data)
+{
+  struct symbol_file_add_from_memory_args *args = data;
+
+  if (vaddr == args->sysinfo_ehdr)
+    {
+      args->size = size;
+      return 1;
+    }
   return 0;
 }
 
@@ -217,6 +236,11 @@ add_vsyscall_page (struct target_ops *target, int from_tty)
 	}
       args.bfd = bfd;
       args.sysinfo_ehdr = sysinfo_ehdr;
+      args.size = 0;
+      if (gdbarch_find_memory_regions_p (target_gdbarch ()))
+	(void) gdbarch_find_memory_regions (target_gdbarch (),
+					    find_vdso_size, &args);
+
       args.name = xstrprintf ("system-supplied DSO at %s",
 			      paddress (target_gdbarch (), sysinfo_ehdr));
       /* Pass zero for FROM_TTY, because the action of loading the