[PATCH v2 2/4] Introduce mmap_file function

Simon Marchi
2018-07-25T22:47:26Z

New in v2:

- As Tom pointed out, we don't need to keep the fd around after
mmapping. This simplifies things quite a bit, since we don't need a
new class. It's now just a function that returns a scoped_mmap.

We already have scoped_mmap, which is a thin RAII layer over mmap. If
one simply wants to mmap an entire file for reading, it takes a bit of
boilerplate. This patch introduces the mmap_file function to make this
easier.

gdb/ChangeLog:

* Makefile.in (COMMON_SFILES): Add common/scoped_mmap.c.
* common/scoped_mmap.c: New file.
* common/scoped_mmap.h (destroy): New method.
(~scoped_mmap, reset): Use destroy.
(scoped_mmap): New move constructor.
(mmap_file): New declaration.
* unittests/scoped_mmap-selftests.c (test_normal,
test_invalid_filename, run_tests): New functions.
(_initialize_scoped_mmap_selftests): Register selftest.
---
gdb/Makefile.in | 1 +
gdb/common/scoped_mmap.c | 44 ++++++++++++++++++++++++++++
gdb/common/scoped_mmap.h | 26 ++++++++++++++---
gdb/unittests/scoped_mmap-selftests.c | 54 +++++++++++++++++++++++++++++++++++
4 files changed, 121 insertions(+), 4 deletions(-)
create mode 100644 gdb/common/scoped_mmap.c

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 8c744d7..915e88c 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -965,6 +965,7 @@ COMMON_SFILES = \
common/ptid.c \
common/rsp-low.c \
common/run-time-clock.c \
+ common/scoped_mmap.c \
common/signals.c \
common/signals-state-save-restore.c \
common/tdesc.c \
diff --git a/gdb/common/scoped_mmap.c b/gdb/common/scoped_mmap.c
new file mode 100644
index 0000000..50ea576
--- /dev/null
+++ b/gdb/common/scoped_mmap.c
@@ -0,0 +1,44 @@
+/* scoped_mmap, automatically unmap files
+
+ Copyright (C) 2018 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/>. */
+
+#include "defs.h"
+#include "scoped_mmap.h"
+#include "scoped_fd.h"
+
+scoped_mmap
+mmap_file (const char *filename)
+{
+ scoped_fd fd (open (filename, O_RDONLY));
+ if (fd.get () < 0)
+ perror_with_name ("open");
+
+ off_t size = lseek (fd.get (), 0, SEEK_END);
+ if (size < 0)
+ perror_with_name ("lseek");
+
+ /* We can't map an empty file. */
+ if (size == 0)
+ error (_("file to mmap is empty"));
+
+ scoped_mmap mmapped_file (nullptr, size, PROT_READ, MAP_PRIVATE, fd.get (), 0);
+ if (mmapped_file.get () == MAP_FAILED)
+ perror_with_name ("mmap");
+
+ return mmapped_file;
+}
diff --git a/gdb/common/scoped_mmap.h b/gdb/common/scoped_mmap.h
index 6070c37..b446163 100644
--- a/gdb/common/scoped_mmap.h
+++ b/gdb/common/scoped_mmap.h
@@ -41,8 +41,18 @@ public:

~scoped_mmap ()
{
- if (m_mem != MAP_FAILED)
- munmap (m_mem, m_length);
+ destroy ();
+ }
+
+ scoped_mmap (scoped_mmap &&rhs)
+ {
+ destroy ();
+
+ m_mem = rhs.m_mem;
+ m_length = rhs.m_length;
+
+ rhs.m_mem = MAP_FAILED;
+ rhs.m_length = 0;
}

DISABLE_COPY_AND_ASSIGN (scoped_mmap);
@@ -58,8 +68,7 @@ public:
void reset (void *addr, size_t length, int prot, int flags, int fd,
off_t offset) noexcept
{
- if (m_mem != MAP_FAILED)
- munmap (m_mem, m_length);
+ destroy ();

m_length = length;
m_mem = mmap (addr, m_length, prot, flags, fd, offset);
@@ -69,9 +78,18 @@ public:
void *get () const noexcept { return m_mem; }

private:
+ void destroy ()
+ {
+ if (m_mem != MAP_FAILED)
+ munmap (m_mem, m_length);
+ }
+
void *m_mem;
size_t m_length;
};

+/* Map FILENAME in memory. Throw an error if anything goes wrong. */
+scoped_mmap mmap_file (const char *filename);
+
#endif /* HAVE_SYS_MMAN_H */
#endif /* SCOPED_MMAP_H */
diff --git a/gdb/unittests/scoped_mmap-selftests.c b/gdb/unittests/scoped_mmap-selftests.c
index ece3d7a..d70a56a 100644
--- a/gdb/unittests/scoped_mmap-selftests.c
+++ b/gdb/unittests/scoped_mmap-selftests.c
@@ -25,6 +25,7 @@
#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_UNISTD_H)

#include "selftest.h"
+#include "common/gdb_unlinker.h"

#include <unistd.h>

@@ -78,6 +79,57 @@ run_tests ()
}

} /* namespace scoped_mmap */
+
+namespace mmap_file
+{
+
+/* Test the standard usage of mmap_file. */
+static void
+test_normal ()
+{
+ char filename[] = "scoped_mmapped_file-selftest-XXXXXX";
+ int fd = mkstemp (filename);
+ SELF_CHECK (fd >= 0);
+
+ write (fd, "Hello!", 7);
+ close (fd);
+
+ gdb::unlinker unlink_test_file (filename);
+
+ {
+ ::scoped_mmap m = ::mmap_file (filename);
+
+ SELF_CHECK (m.get () != MAP_FAILED);
+ SELF_CHECK (m.size () == 7);
+ SELF_CHECK (0 == strcmp ((char *) m.get (), "Hello!"));
+ }
+}
+
+/* Calling mmap_file with a non-existent file should throw an exception. */
+static void
+test_invalid_filename ()
+{
+ bool threw = false;
+
+ try {
+ ::scoped_mmap m = ::mmap_file ("/this/file/should/not/exist");
+ } catch (gdb_exception &e) {
+ threw = true;
+ }
+
+ SELF_CHECK (threw);
+}
+
+
+/* Run selftests. */
+static void
+run_tests ()
+{
+ test_normal ();
+ test_invalid_filename ();
+}
+
+} /* namespace mmap_file */
} /* namespace selftests */

#endif /* !defined(HAVE_SYS_MMAN_H) || !defined(HAVE_UNISTD_H) */
@@ -88,5 +140,7 @@ _initialize_scoped_mmap_selftests ()
#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_UNISTD_H)
selftests::register_test ("scoped_mmap",
selftests::scoped_mmap::run_tests);
+ selftests::register_test ("mmap_file",
+ selftests::mmap_file::run_tests);
#endif
}
--
2.7.4