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[rfa:symtab] Delete broken "memory mapped objfile cache"
- From: Andrew Cagney <ac131313 at redhat dot com>
- To: gdb-patches at sources dot redhat dot com
- Date: Tue, 04 Nov 2003 11:21:22 -0500
- Subject: [rfa:symtab] Delete broken "memory mapped objfile cache"
Hello,
(more, somewhat perverse bcache fallout)
The "memory mapped objfile cache" (for want of a better name) is a
technique where by GDB creates per-objfile disk backed memory mapped
caches that contain the object files symbol information. Its based on
the theory that, after each rebuild little is changed, and hence most
symbol information can be drawn from an on-disk cache, and re-read from
the object file. The lit, it turns out, supports the theory. A typical
debugging rebuild changes little in an executable.
So why delete it? As far as I can tell:
- it hasn't worked in >4years
- it hasn't built in >1year
- it isn't tested
I've nothing personal against the the technique. In fact I'd like to
see a robust implementation backed by test cases and supporting
performance data. However, I strongly object to GDB having to carry
around long-ago broken code. By deleting this, we clear the decks for a
modern robust implementation (the original code appears to date back to
'92).
Rationale:
The original bcache was implemented using a per-object file obstack and
a finite sized table. Then in _1999_ the bcache was rewritten [fixed]
so that it could use a growable hash table. The hash table being
allocated using xmalloc.
So? The "mapped" code, as far as I can tell, relies on all the
per-object file data being drawn from a per-object file memory-mapped
memory pool. The bcache fixes [unintentionally] broke that assumption.
The bcached data (in particular the partial symbol table) was moved to
the global memory pool making the re-mapping of a per-object file
structure anything but robust :-(. Hence, I don't believe this has
worked for >4years.
But wait, there's more ...
In _2003-07-12_ the bcache code was cleaned up, making the "struct
bcache" opaque. Life was good.
So? Well, it turns out that the "mapped" code was grubbing around in
bcache internals and the change [unintentionally] broke that ability
leaving the "mapped" code unbuildable for >1year!
ok to commit?
Andrew
PS: Note that I'll also need to update the documentation
2003-11-02 Andrew Cagney <cagney@redhat.com>
* top.h (mapped_symbol_files): Delete declaration.
* main.c (captured_main): Delete option "m" and "mapped".
* objfiles.c (mapped_symbol_files): Delete variable.
* symfile.c (symbol_file_command): Delete mmap code.
(symbol_file_add_with_addrs_or_offsets): Ditto.
(add_symbol_file_command, reread_separate_symbols): Ditto.
* objfiles.h (OBJF_MAPPED): Delete.
* objfiles.c (allocate_objfile) [USE_MMALLOC]: Delete.
(free_objfile) [USE_MMALLOC]: Ditto.
(open_existing_mapped_file): Delete function.
(open_mapped_file): Delete function.
(map_to_file): Delete function.
Index: main.c
===================================================================
RCS file: /cvs/src/src/gdb/main.c,v
retrieving revision 1.36
diff -u -r1.36 main.c
--- main.c 14 Sep 2003 16:32:13 -0000 1.36
+++ main.c 4 Nov 2003 15:09:29 -0000
@@ -264,8 +264,6 @@
{"dbx", no_argument, &dbx_commands, 1},
{"readnow", no_argument, &readnow_symbol_files, 1},
{"r", no_argument, &readnow_symbol_files, 1},
- {"mapped", no_argument, &mapped_symbol_files, 1},
- {"m", no_argument, &mapped_symbol_files, 1},
{"quiet", no_argument, &quiet, 1},
{"q", no_argument, &quiet, 1},
{"silent", no_argument, &quiet, 1},
Index: objfiles.c
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.c,v
retrieving revision 1.39
diff -u -r1.39 objfiles.c
--- objfiles.c 29 Oct 2003 18:29:07 -0000 1.39
+++ objfiles.c 4 Nov 2003 15:09:29 -0000
@@ -48,18 +48,6 @@
/* Prototypes for local functions */
-#if defined(USE_MMALLOC) && defined(HAVE_MMAP)
-
-#include "mmalloc.h"
-
-static int open_existing_mapped_file (char *, long, int);
-
-static int open_mapped_file (char *filename, long mtime, int flags);
-
-static void *map_to_file (int);
-
-#endif /* defined(USE_MMALLOC) && defined(HAVE_MMAP) */
-
static void add_to_objfile_sections (bfd *, sec_ptr, void *);
static void objfile_alloc_data (struct objfile *objfile);
@@ -73,8 +61,6 @@
struct objfile *symfile_objfile; /* Main symbol table loaded from */
struct objfile *rt_common_objfile; /* For runtime common symbols */
-int mapped_symbol_files; /* Try to use mapped symbol files */
-
/* Locate all mappable sections of a BFD file.
objfile_p_char is a char * to get it through
bfd_map_over_sections; we cast it back to its proper type. */
@@ -151,10 +137,8 @@
new objfile struct.
The FLAGS word contains various bits (OBJF_*) that can be taken as
- requests for specific operations, like trying to open a mapped
- version of the objfile (OBJF_MAPPED). Other bits like
- OBJF_SHARED are simply copied through to the new objfile flags
- member. */
+ requests for specific operations. Other bits like OBJF_SHARED are
+ simply copied through to the new objfile flags member. */
/* NOTE: carlton/2003-02-04: This function is called with args NULL, 0
by jv-lang.c, to create an artificial objfile used to hold
@@ -171,119 +155,6 @@
struct objfile *objfile = NULL;
struct objfile *last_one = NULL;
- if (mapped_symbol_files)
- flags |= OBJF_MAPPED;
-
-#if defined(USE_MMALLOC) && defined(HAVE_MMAP)
- if (abfd != NULL)
- {
-
- /* If we can support mapped symbol files, try to open/reopen the
- mapped file that corresponds to the file from which we wish to
- read symbols. If the objfile is to be mapped, we must malloc
- the structure itself using the mmap version, and arrange that
- all memory allocation for the objfile uses the mmap routines.
- If we are reusing an existing mapped file, from which we get
- our objfile pointer, we have to make sure that we update the
- pointers to the alloc/free functions in the obstack, in case
- these functions have moved within the current gdb. */
-
- int fd;
-
- fd = open_mapped_file (bfd_get_filename (abfd), bfd_get_mtime (abfd),
- flags);
- if (fd >= 0)
- {
- void *md;
-
- if ((md = map_to_file (fd)) == NULL)
- {
- close (fd);
- }
- else if ((objfile = (struct objfile *) mmalloc_getkey (md, 0)) != NULL)
- {
- /* Update memory corruption handler function addresses. */
- init_malloc (md);
- objfile->md = md;
- objfile->mmfd = fd;
- /* Update pointers to functions to *our* copies */
- if (objfile->demangled_names_hash)
- htab_set_functions_ex
- (objfile->demangled_names_hash, htab_hash_string,
- (int (*) (const void *, const void *)) streq, NULL,
- objfile->md, xmcalloc, xmfree);
- obstack_chunkfun (&objfile->psymbol_cache.cache, xmmalloc);
- obstack_freefun (&objfile->psymbol_cache.cache, xmfree);
- obstack_chunkfun (&objfile->macro_cache.cache, xmmalloc);
- obstack_freefun (&objfile->macro_cache.cache, xmfree);
- obstack_chunkfun (&objfile->psymbol_obstack, xmmalloc);
- obstack_freefun (&objfile->psymbol_obstack, xmfree);
- obstack_chunkfun (&objfile->symbol_obstack, xmmalloc);
- obstack_freefun (&objfile->symbol_obstack, xmfree);
- obstack_chunkfun (&objfile->type_obstack, xmmalloc);
- obstack_freefun (&objfile->type_obstack, xmfree);
- /* If already in objfile list, unlink it. */
- unlink_objfile (objfile);
- /* Forget things specific to a particular gdb, may have changed. */
- objfile->sf = NULL;
- }
- else
- {
-
- /* Set up to detect internal memory corruption. MUST be
- done before the first malloc. See comments in
- init_malloc() and mmcheck(). */
-
- init_malloc (md);
-
- objfile = (struct objfile *)
- xmmalloc (md, sizeof (struct objfile));
- memset (objfile, 0, sizeof (struct objfile));
- objfile->md = md;
- objfile->mmfd = fd;
- objfile->flags |= OBJF_MAPPED;
- mmalloc_setkey (objfile->md, 0, objfile);
- obstack_specify_allocation_with_arg (&objfile->psymbol_cache.cache,
- 0, 0, xmmalloc, xmfree,
- objfile->md);
- obstack_specify_allocation_with_arg (&objfile->macro_cache.cache,
- 0, 0, xmmalloc, xmfree,
- objfile->md);
- obstack_specify_allocation_with_arg (&objfile->psymbol_obstack,
- 0, 0, xmmalloc, xmfree,
- objfile->md);
- obstack_specify_allocation_with_arg (&objfile->symbol_obstack,
- 0, 0, xmmalloc, xmfree,
- objfile->md);
- obstack_specify_allocation_with_arg (&objfile->type_obstack,
- 0, 0, xmmalloc, xmfree,
- objfile->md);
- }
- }
-
- if ((flags & OBJF_MAPPED) && (objfile == NULL))
- {
- warning ("symbol table for '%s' will not be mapped",
- bfd_get_filename (abfd));
- flags &= ~OBJF_MAPPED;
- }
- }
-#else /* !defined(USE_MMALLOC) || !defined(HAVE_MMAP) */
-
- if (flags & OBJF_MAPPED)
- {
- warning ("mapped symbol tables are not supported on this machine; missing or broken mmap().");
-
- /* Turn off the global flag so we don't try to do mapped symbol tables
- any more, which shuts up gdb unless the user specifically gives the
- "mapped" keyword again. */
-
- mapped_symbol_files = 0;
- flags &= ~OBJF_MAPPED;
- }
-
-#endif /* defined(USE_MMALLOC) && defined(HAVE_MMAP) */
-
/* If we don't support mapped symbol files, didn't ask for the file to be
mapped, or failed to open the mapped file for some reason, then revert
back to an unmapped objfile. */
@@ -301,7 +172,6 @@
xfree);
obstack_specify_allocation (&objfile->type_obstack, 0, 0, xmalloc,
xfree);
- flags &= ~OBJF_MAPPED;
terminate_minimal_symbol_table (objfile);
}
@@ -545,52 +415,27 @@
to call this here. */
clear_pc_function_cache ();
- /* The last thing we do is free the objfile struct itself for the
- non-reusable case, or detach from the mapped file for the
- reusable case. Note that the mmalloc_detach or the xmfree() is
- the last thing we can do with this objfile. */
-
-#if defined(USE_MMALLOC) && defined(HAVE_MMAP)
-
- if (objfile->flags & OBJF_MAPPED)
- {
- /* Remember the fd so we can close it. We can't close it before
- doing the detach, and after the detach the objfile is gone. */
- int mmfd;
-
- mmfd = objfile->mmfd;
- mmalloc_detach (objfile->md);
- objfile = NULL;
- close (mmfd);
- }
-
-#endif /* defined(USE_MMALLOC) && defined(HAVE_MMAP) */
-
- /* If we still have an objfile, then either we don't support reusable
- objfiles or this one was not reusable. So free it normally. */
+ /* The last thing we do is free the objfile struct itself. */
- if (objfile != NULL)
+ objfile_free_data (objfile);
+ if (objfile->name != NULL)
{
- objfile_free_data (objfile);
- if (objfile->name != NULL)
- {
- xmfree (objfile->md, objfile->name);
- }
- if (objfile->global_psymbols.list)
- xmfree (objfile->md, objfile->global_psymbols.list);
- if (objfile->static_psymbols.list)
- xmfree (objfile->md, objfile->static_psymbols.list);
- /* Free the obstacks for non-reusable objfiles */
- bcache_xfree (objfile->psymbol_cache);
- bcache_xfree (objfile->macro_cache);
- if (objfile->demangled_names_hash)
- htab_delete (objfile->demangled_names_hash);
- obstack_free (&objfile->psymbol_obstack, 0);
- obstack_free (&objfile->symbol_obstack, 0);
- obstack_free (&objfile->type_obstack, 0);
- xmfree (objfile->md, objfile);
- objfile = NULL;
+ xmfree (objfile->md, objfile->name);
}
+ if (objfile->global_psymbols.list)
+ xmfree (objfile->md, objfile->global_psymbols.list);
+ if (objfile->static_psymbols.list)
+ xmfree (objfile->md, objfile->static_psymbols.list);
+ /* Free the obstacks for non-reusable objfiles */
+ bcache_xfree (objfile->psymbol_cache);
+ bcache_xfree (objfile->macro_cache);
+ if (objfile->demangled_names_hash)
+ htab_delete (objfile->demangled_names_hash);
+ obstack_free (&objfile->psymbol_obstack, 0);
+ obstack_free (&objfile->symbol_obstack, 0);
+ obstack_free (&objfile->type_obstack, 0);
+ xmfree (objfile->md, objfile);
+ objfile = NULL;
}
static void
@@ -881,168 +726,6 @@
}
return 0;
}
-
-#if defined(USE_MMALLOC) && defined(HAVE_MMAP)
-
-/* Given the name of a mapped symbol file in SYMSFILENAME, and the timestamp
- of the corresponding symbol file in MTIME, try to open an existing file
- with the name SYMSFILENAME and verify it is more recent than the base
- file by checking it's timestamp against MTIME.
-
- If SYMSFILENAME does not exist (or can't be stat'd), simply returns -1.
-
- If SYMSFILENAME does exist, but is out of date, we check to see if the
- user has specified creation of a mapped file. If so, we don't issue
- any warning message because we will be creating a new mapped file anyway,
- overwriting the old one. If not, then we issue a warning message so that
- the user will know why we aren't using this existing mapped symbol file.
- In either case, we return -1.
-
- If SYMSFILENAME does exist and is not out of date, but can't be opened for
- some reason, then prints an appropriate system error message and returns -1.
-
- Otherwise, returns the open file descriptor. */
-
-static int
-open_existing_mapped_file (char *symsfilename, long mtime, int flags)
-{
- int fd = -1;
- struct stat sbuf;
-
- if (stat (symsfilename, &sbuf) == 0)
- {
- if (sbuf.st_mtime < mtime)
- {
- if (!(flags & OBJF_MAPPED))
- {
- warning ("mapped symbol file `%s' is out of date, ignored it",
- symsfilename);
- }
- }
- else if ((fd = open (symsfilename, O_RDWR)) < 0)
- {
- if (error_pre_print)
- {
- printf_unfiltered (error_pre_print);
- }
- print_sys_errmsg (symsfilename, errno);
- }
- }
- return (fd);
-}
-
-/* Look for a mapped symbol file that corresponds to FILENAME and is more
- recent than MTIME. If MAPPED is nonzero, the user has asked that gdb
- use a mapped symbol file for this file, so create a new one if one does
- not currently exist.
-
- If found, then return an open file descriptor for the file, otherwise
- return -1.
-
- This routine is responsible for implementing the policy that generates
- the name of the mapped symbol file from the name of a file containing
- symbols that gdb would like to read. Currently this policy is to append
- ".syms" to the name of the file.
-
- This routine is also responsible for implementing the policy that
- determines where the mapped symbol file is found (the search path).
- This policy is that when reading an existing mapped file, a file of
- the correct name in the current directory takes precedence over a
- file of the correct name in the same directory as the symbol file.
- When creating a new mapped file, it is always created in the current
- directory. This helps to minimize the chances of a user unknowingly
- creating big mapped files in places like /bin and /usr/local/bin, and
- allows a local copy to override a manually installed global copy (in
- /bin for example). */
-
-static int
-open_mapped_file (char *filename, long mtime, int flags)
-{
- int fd;
- char *symsfilename;
-
- /* First try to open an existing file in the current directory, and
- then try the directory where the symbol file is located. */
-
- symsfilename = concat ("./", lbasename (filename), ".syms", (char *) NULL);
- if ((fd = open_existing_mapped_file (symsfilename, mtime, flags)) < 0)
- {
- xfree (symsfilename);
- symsfilename = concat (filename, ".syms", (char *) NULL);
- fd = open_existing_mapped_file (symsfilename, mtime, flags);
- }
-
- /* If we don't have an open file by now, then either the file does not
- already exist, or the base file has changed since it was created. In
- either case, if the user has specified use of a mapped file, then
- create a new mapped file, truncating any existing one. If we can't
- create one, print a system error message saying why we can't.
-
- By default the file is rw for everyone, with the user's umask taking
- care of turning off the permissions the user wants off. */
-
- if ((fd < 0) && (flags & OBJF_MAPPED))
- {
- xfree (symsfilename);
- symsfilename = concat ("./", lbasename (filename), ".syms",
- (char *) NULL);
- if ((fd = open (symsfilename, O_RDWR | O_CREAT | O_TRUNC, 0666)) < 0)
- {
- if (error_pre_print)
- {
- printf_unfiltered (error_pre_print);
- }
- print_sys_errmsg (symsfilename, errno);
- }
- }
-
- xfree (symsfilename);
- return (fd);
-}
-
-static void *
-map_to_file (int fd)
-{
- void *md;
- CORE_ADDR mapto;
-
- md = mmalloc_attach (fd, 0);
- if (md != NULL)
- {
- mapto = (CORE_ADDR) mmalloc_getkey (md, 1);
- md = mmalloc_detach (md);
- if (md != NULL)
- {
- /* FIXME: should figure out why detach failed */
- md = NULL;
- }
- else if (mapto != (CORE_ADDR) NULL)
- {
- /* This mapping file needs to be remapped at "mapto" */
- md = mmalloc_attach (fd, mapto);
- }
- else
- {
- /* This is a freshly created mapping file. */
- mapto = (CORE_ADDR) mmalloc_findbase (20 * 1024 * 1024);
- if (mapto != 0)
- {
- /* To avoid reusing the freshly created mapping file, at the
- address selected by mmap, we must truncate it before trying
- to do an attach at the address we want. */
- ftruncate (fd, 0);
- md = mmalloc_attach (fd, mapto);
- if (md != NULL)
- {
- mmalloc_setkey (md, 1, mapto);
- }
- }
- }
- }
- return (md);
-}
-
-#endif /* defined(USE_MMALLOC) && defined(HAVE_MMAP) */
/* Returns a section whose range includes PC and SECTION, or NULL if
none found. Note the distinction between the return type, struct
Index: objfiles.h
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.h,v
retrieving revision 1.27
diff -u -r1.27 objfiles.h
--- objfiles.h 29 Oct 2003 18:29:07 -0000 1.27
+++ objfiles.h 4 Nov 2003 15:09:29 -0000
@@ -470,15 +470,6 @@
/* Defines for the objfile flag word. */
-/* Gdb can arrange to allocate storage for all objects related to a
- particular objfile in a designated section of its address space,
- managed at a low level by mmap() and using a special version of
- malloc that handles malloc/free/realloc on top of the mmap() interface.
- This allows the "internal gdb state" for a particular objfile to be
- dumped to a gdb state file and subsequently reloaded at a later time. */
-
-#define OBJF_MAPPED (1 << 0) /* Objfile data is mmap'd */
-
/* When using mapped/remapped predigested gdb symbol information, we need
a flag that indicates that we have previously done an initial symbol
table read from this particular objfile. We can't just look for the
Index: symfile.c
===================================================================
RCS file: /cvs/src/src/gdb/symfile.c,v
retrieving revision 1.111
diff -u -r1.111 symfile.c
--- symfile.c 29 Oct 2003 18:29:07 -0000 1.111
+++ symfile.c 4 Nov 2003 15:09:37 -0000
@@ -861,43 +861,22 @@
orig_addrs->other[i] = addrs->other[i];
}
- /* If the objfile uses a mapped symbol file, and we have a psymtab for
- it, then skip reading any symbols at this time. */
-
- if ((objfile->flags & OBJF_MAPPED) && (objfile->flags & OBJF_SYMS))
+ /* We either created a new mapped symbol table, mapped an existing
+ symbol table file which has not had initial symbol reading
+ performed, or need to read an unmapped symbol table. */
+ if (from_tty || info_verbose)
{
- /* We mapped in an existing symbol table file that already has had
- initial symbol reading performed, so we can skip that part. Notify
- the user that instead of reading the symbols, they have been mapped.
- */
- if (from_tty || info_verbose)
+ if (pre_add_symbol_hook)
+ pre_add_symbol_hook (name);
+ else
{
- printf_unfiltered ("Mapped symbols for %s...", name);
+ printf_unfiltered ("Reading symbols from %s...", name);
wrap_here ("");
gdb_flush (gdb_stdout);
}
- init_entry_point_info (objfile);
- find_sym_fns (objfile);
- }
- else
- {
- /* We either created a new mapped symbol table, mapped an existing
- symbol table file which has not had initial symbol reading
- performed, or need to read an unmapped symbol table. */
- if (from_tty || info_verbose)
- {
- if (pre_add_symbol_hook)
- pre_add_symbol_hook (name);
- else
- {
- printf_unfiltered ("Reading symbols from %s...", name);
- wrap_here ("");
- gdb_flush (gdb_stdout);
- }
- }
- syms_from_objfile (objfile, addrs, offsets, num_offsets,
- mainline, from_tty);
}
+ syms_from_objfile (objfile, addrs, offsets, num_offsets,
+ mainline, from_tty);
/* We now have at least a partial symbol table. Check to see if the
user requested that all symbols be read on initial access via either
@@ -1223,20 +1202,16 @@
cleanups = make_cleanup_freeargv (argv);
while (*argv != NULL)
{
- if (STREQ (*argv, "-mapped"))
- flags |= OBJF_MAPPED;
- else
- if (STREQ (*argv, "-readnow"))
- flags |= OBJF_READNOW;
- else
- if (**argv == '-')
- error ("unknown option `%s'", *argv);
- else
- {
- name = *argv;
-
- symbol_file_add_main_1 (name, from_tty, flags);
- }
+ if (STREQ (*argv, "-readnow"))
+ flags |= OBJF_READNOW;
+ else if (**argv == '-')
+ error ("unknown option `%s'", *argv);
+ else
+ {
+ name = *argv;
+
+ symbol_file_add_main_1 (name, from_tty, flags);
+ }
argv++;
}
@@ -1751,17 +1726,14 @@
if (*arg == '-')
{
- if (strcmp (arg, "-mapped") == 0)
- flags |= OBJF_MAPPED;
+ if (strcmp (arg, "-readnow") == 0)
+ flags |= OBJF_READNOW;
else
- if (strcmp (arg, "-readnow") == 0)
- flags |= OBJF_READNOW;
- else
- if (strcmp (arg, "-s") == 0)
- {
- expecting_sec_name = 1;
- expecting_sec_addr = 1;
- }
+ if (strcmp (arg, "-s") == 0)
+ {
+ expecting_sec_name = 1;
+ expecting_sec_addr = 1;
+ }
}
else
{
@@ -2110,8 +2082,7 @@
0, /* No addr table. */
objfile->section_offsets, objfile->num_sections,
0, /* Not mainline. See comments about this above. */
- objfile->flags & (OBJF_MAPPED | OBJF_REORDERED
- | OBJF_SHARED | OBJF_READNOW
+ objfile->flags & (OBJF_REORDERED | OBJF_SHARED | OBJF_READNOW
| OBJF_USERLOADED)));
objfile->separate_debug_objfile->separate_debug_objfile_backlink
= objfile;
Index: top.h
===================================================================
RCS file: /cvs/src/src/gdb/top.h,v
retrieving revision 1.9
diff -u -r1.9 top.h
--- top.h 8 Jun 2003 18:27:14 -0000 1.9
+++ top.h 4 Nov 2003 15:09:37 -0000
@@ -56,7 +56,6 @@
extern void set_prompt (char *);
/* From random places. */
-extern int mapped_symbol_files;
extern int readnow_symbol_files;
/* Perform _initialize initialization */