binutils-gdb/gdb/gdb_bfd.h
Pedro Alves 98c59b527b Make exec-file-mismatch compare build IDs
The patch makes GDB do exec-file-mismatch validation by comparing
build IDs instead of the current method of comparing filenames.

Currently, the exec-file-mismatch feature simply compares filenames to
decide whether the exec file loaded in gdb and the exec file the
target reports is running match.  This causes false positives when
remote debugging, because it'll often be the case that the paths in
the host and the target won't match.  And of course misses the case of
the files having the same name but being actually different files
(e.g., different builds).

This also broke many testcases when running against gdbserver, causing
tests to be skipped like (here native-extended-gdbserver):

  (gdb) run
  Starting program: /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink-filelink
  warning: Mismatch between current exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink-filelink
  and automatically determined exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink
  exec-file-mismatch handling is currently "ask"
  Load new symbol table from "/home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink"? (y or n) UNTESTED: gdb.base/argv0-symlink.exp: could not run to main

or to fail like (here native-gdbserver):

 (gdb) spawn /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/../../gdbserver/gdbserver --once localhost:2346 /home/pedro/gdb/binutils-gdb/build/gdb/te
 stsuite/outputs/gdb.btrace/buffer-size/skip_btrace_tests-19968.x
 Process /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.btrace/buffer-size/skip_btrace_tests-19968.x created; pid = 20040
 Listening on port 2346
 target remote localhost:2346
 Remote debugging using localhost:2346
 warning: Mismatch between current exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/temp/19968/skip_btrace_tests-19968.x
 and automatically determined exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.btrace/buffer-size/skip_btrace_tests-19968.x
 exec-file-mismatch handling is currently "ask"
 Load new symbol table from "/home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.btrace/buffer-size/skip_btrace_tests-19968.x"? (y or n) Quit
 (gdb) UNSUPPORTED: gdb.btrace/buffer-size.exp: target does not support record-btrace

The former case is about GDB not realizing the two files are the same,
because one of the them is a symlink to the other.  The latter case is
about GDB realizing that one file is a copy of the other.

Over the years, the toolchain has settled on build ID matching being
the canonical method to match core dumps to executables, and
executables with no debug info to their debug info.

This patch makes us use build IDs to match the running image of a
binary with its version loaded in gdb, which may or may not have debug
info.  This is very much like the core dump/executable matching.

The change to gdb_bfd_open is necessary to get rid of the "transfers
from remote targets can be slow" warning when we open the remote file
to read its build ID:

 (gdb) r
 Starting program: /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/break/break
 Reading /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink from remote target...
 warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead.
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 warning: Mismatch between current exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/break/break
 and automatically determined exec-file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink
 exec-file-mismatch handling is currently "ask"
 Load new symbol table from "/home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.base/argv0-symlink/argv0-symlink"? (y or n)

While trying this out, I was worried that bfd would read a lot of
stuff from the binary in order to extract the build ID, making it
potentially slow, but turns out we don't read all that much.  Maybe a
couple hundred bytes, and most of it seemingly is the read-ahead
cache.  So I'm not worried about that.  Otherwise I'd consider whether
a new qXfer:buildid:read would be better.  But I'm happy that we
seemingly don't need to worry about it.

gdb/ChangeLog:
2020-05-19  Pedro Alves  <palves@redhat.com>

	* NEWS (set exec-file-mismatch): Adjust entry.
	* exec.c: Include "build-id.h".
	(validate_exec_file): Try to match build IDs instead of filenames.
	* gdb_bfd.c (struct gdb_bfd_open_closure): New.
	(gdb_bfd_iovec_fileio_open): Adjust to use gdb_bfd_open_closure
	and pass down 'warn_if_slow'.
	(gdb_bfd_open): Add 'warn_if_slow' parameter.  Use
	gdb_bfd_open_closure to pass it down.
	* gdb_bfd.h (gdb_bfd_open): Add 'warn_if_slow' parameter.

gdb/doc/ChangeLog:
2020-05-19  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Attach): Update exec-file-mismatch description to
	mention build IDs.
	(Separate Debug Files): Add "build id" anchor.
2020-05-19 18:37:15 +01:00

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/* Definitions for BFD wrappers used by GDB.
Copyright (C) 2011-2020 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef GDB_BFD_H
#define GDB_BFD_H
#include "registry.h"
#include "gdbsupport/byte-vector.h"
#include "gdbsupport/gdb_ref_ptr.h"
DECLARE_REGISTRY (bfd);
/* If supplied a path starting with this sequence, gdb_bfd_open will
open BFDs using target fileio operations. */
#define TARGET_SYSROOT_PREFIX "target:"
/* Returns nonzero if NAME starts with TARGET_SYSROOT_PREFIX, zero
otherwise. */
int is_target_filename (const char *name);
/* Returns nonzero if the filename associated with ABFD starts with
TARGET_SYSROOT_PREFIX, zero otherwise. */
int gdb_bfd_has_target_filename (struct bfd *abfd);
/* Increment the reference count of ABFD. It is fine for ABFD to be
NULL; in this case the function does nothing. */
void gdb_bfd_ref (struct bfd *abfd);
/* Decrement the reference count of ABFD. If this is the last
reference, ABFD will be freed. If ABFD is NULL, this function does
nothing. */
void gdb_bfd_unref (struct bfd *abfd);
/* A policy class for gdb::ref_ptr for BFD reference counting. */
struct gdb_bfd_ref_policy
{
static void incref (struct bfd *abfd)
{
gdb_bfd_ref (abfd);
}
static void decref (struct bfd *abfd)
{
gdb_bfd_unref (abfd);
}
};
/* A gdb::ref_ptr that has been specialized for BFD objects. */
typedef gdb::ref_ptr<struct bfd, gdb_bfd_ref_policy> gdb_bfd_ref_ptr;
/* Open a read-only (FOPEN_RB) BFD given arguments like bfd_fopen.
If NAME starts with TARGET_SYSROOT_PREFIX then the BFD will be
opened using target fileio operations if necessary. Returns NULL
on error. On success, returns a new reference to the BFD. BFDs
returned by this call are shared among all callers opening the same
file. If FD is not -1, then after this call it is owned by BFD.
If the BFD was not accessed using target fileio operations then the
filename associated with the BFD and accessible with
bfd_get_filename will not be exactly NAME but rather NAME with
TARGET_SYSROOT_PREFIX stripped. If WARN_IF_SLOW is true, print a
warning message if the file is being accessed over a link that may
be slow. */
gdb_bfd_ref_ptr gdb_bfd_open (const char *name, const char *target,
int fd = -1, bool warn_if_slow = true);
/* Mark the CHILD BFD as being a member of PARENT. Also, increment
the reference count of CHILD. Calling this function ensures that
as along as CHILD remains alive, PARENT will as well. Both CHILD
and PARENT must be non-NULL. This can be called more than once
with the same arguments; but it is not allowed to call it for a
single CHILD with different values for PARENT. */
void gdb_bfd_mark_parent (bfd *child, bfd *parent);
/* Mark INCLUDEE as being included by INCLUDER.
This is used to associate the life time of INCLUDEE with INCLUDER.
For example, with Fission, one file can refer to debug info in another
file, and internal tables we build for the main file (INCLUDER) may refer
to data contained in INCLUDEE. Therefore we want to keep INCLUDEE around
at least as long as INCLUDER exists.
Note that this is different than gdb_bfd_mark_parent because in our case
lifetime tracking is based on the "parent" whereas in gdb_bfd_mark_parent
lifetime tracking is based on the "child". Plus in our case INCLUDEE could
have multiple different "parents". */
void gdb_bfd_record_inclusion (bfd *includer, bfd *includee);
/* Try to read or map the contents of the section SECT. If successful, the
section data is returned and *SIZE is set to the size of the section data;
this may not be the same as the size according to bfd_section_size if the
section was compressed. The returned section data is associated with the BFD
and will be destroyed when the BFD is destroyed. There is no other way to
free it; for temporary uses of section data, see bfd_malloc_and_get_section.
SECT may not have relocations. If there is an error reading the section,
this issues a warning, sets *SIZE to 0, and returns NULL. */
const gdb_byte *gdb_bfd_map_section (asection *section, bfd_size_type *size);
/* Compute the CRC for ABFD. The CRC is used to find and verify
separate debug files. When successful, this fills in *CRC_OUT and
returns 1. Otherwise, this issues a warning and returns 0. */
int gdb_bfd_crc (struct bfd *abfd, unsigned long *crc_out);
/* A wrapper for bfd_fopen that initializes the gdb-specific reference
count. */
gdb_bfd_ref_ptr gdb_bfd_fopen (const char *, const char *, const char *, int);
/* A wrapper for bfd_openr that initializes the gdb-specific reference
count. */
gdb_bfd_ref_ptr gdb_bfd_openr (const char *, const char *);
/* A wrapper for bfd_openw that initializes the gdb-specific reference
count. */
gdb_bfd_ref_ptr gdb_bfd_openw (const char *, const char *);
/* A wrapper for bfd_openr_iovec that initializes the gdb-specific
reference count. */
gdb_bfd_ref_ptr gdb_bfd_openr_iovec (const char *filename, const char *target,
void *(*open_func) (struct bfd *nbfd,
void *open_closure),
void *open_closure,
file_ptr (*pread_func) (struct bfd *nbfd,
void *stream,
void *buf,
file_ptr nbytes,
file_ptr offset),
int (*close_func) (struct bfd *nbfd,
void *stream),
int (*stat_func) (struct bfd *abfd,
void *stream,
struct stat *sb));
/* A wrapper for bfd_openr_next_archived_file that initializes the
gdb-specific reference count. */
gdb_bfd_ref_ptr gdb_bfd_openr_next_archived_file (bfd *archive, bfd *previous);
/* Return the index of the BFD section SECTION. Ordinarily this is
just the section's index, but for some special sections, like
bfd_com_section_ptr, it will be a synthesized value. */
int gdb_bfd_section_index (bfd *abfd, asection *section);
/* Like bfd_count_sections, but include any possible global sections,
like bfd_com_section_ptr. */
int gdb_bfd_count_sections (bfd *abfd);
/* Return true if any section requires relocations, false
otherwise. */
int gdb_bfd_requires_relocations (bfd *abfd);
/* Alternative to bfd_get_full_section_contents that returns the section
contents in *CONTENTS, instead of an allocated buffer.
Return true on success, false otherwise. */
bool gdb_bfd_get_full_section_contents (bfd *abfd, asection *section,
gdb::byte_vector *contents);
#endif /* GDB_BFD_H */