[PATCH v3 0/3] Update FreeBSD's syscall table

This removes the need for the caller to explicitly manage the memory
for the returned system call list. The sole caller only needed the
system call numbers rather than the full syscall structures.

get_syscalls_by_group now uses a boolean return value to indicate if
the requested group exists.

gdb/ChangeLog:

* break-catch-syscall.c (catch_syscall_split_args): Pass 'result'
to get_syscalls_by_group.
* xml-syscall.c [!HAVE_LIBEXPAT] (get_syscalls_by_group): Return
false.
[HAVE_LIBEXPAT] (xml_list_syscalls_by_group): Append syscall
numbers to an existing vector of integers and return a bool.
(get_syscalls_by_group): Accept reference to vector of integers
and change return type to bool.
* xml-syscall.h (get_syscalls_by_group): Likewise.
---
gdb/ChangeLog | 12 ++++++++++
gdb/break-catch-syscall.c | 14 +-----------
gdb/xml-syscall.c | 47 +++++++++++++++------------------------
gdb/xml-syscall.h | 10 ++++-----
4 files changed, 35 insertions(+), 48 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b6c612bd0b..81faa2994d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,15 @@
+2018-11-09 John Baldwin <***@FreeBSD.org>
+
+ * break-catch-syscall.c (catch_syscall_split_args): Pass 'result'
+ to get_syscalls_by_group.
+ * xml-syscall.c [!HAVE_LIBEXPAT] (get_syscalls_by_group): Return
+ false.
+ [HAVE_LIBEXPAT] (xml_list_syscalls_by_group): Append syscall
+ numbers to an existing vector of integers and return a bool.
+ (get_syscalls_by_group): Accept reference to vector of integers
+ and change return type to bool.
+ * xml-syscall.h (get_syscalls_by_group): Likewise.
+
2018-11-09 Hafiz Abid Qadeer <***@codesourcery.com>

* configure: Regenerate.
diff --git a/gdb/break-catch-syscall.c b/gdb/break-catch-syscall.c
index 93ef74c249..f3740a1673 100644
--- a/gdb/break-catch-syscall.c
+++ b/gdb/break-catch-syscall.c
@@ -409,25 +409,13 @@ catch_syscall_split_args (const char *arg)
{
/* We have a syscall group. Let's expand it into a syscall
list before inserting. */
- struct syscall *syscall_list;
const char *group_name;

/* Skip over "g:" and "group:" prefix strings. */
group_name = strchr (cur_name, ':') + 1;

- syscall_list = get_syscalls_by_group (gdbarch, group_name);
-
- if (syscall_list == NULL)
+ if (!get_syscalls_by_group (gdbarch, group_name, result))
error (_("Unknown syscall group '%s'."), group_name);
-
- for (i = 0; syscall_list[i].name != NULL; i++)
- {
- /* Insert each syscall that are part of the group. No
- need to check if it is valid. */
- result.push_back (syscall_list[i].number);
- }
-
- xfree (syscall_list);
}
else
{
diff --git a/gdb/xml-syscall.c b/gdb/xml-syscall.c
index bf17642911..664cee77dd 100644
--- a/gdb/xml-syscall.c
+++ b/gdb/xml-syscall.c
@@ -77,11 +77,12 @@ get_syscall_names (struct gdbarch *gdbarch)
return NULL;
}

-struct syscall *
-get_syscalls_by_group (struct gdbarch *gdbarch, const char *group)
+bool
+get_syscalls_by_group (struct gdbarch *gdbarch, const char *group,
+ std::vector<int> &syscall_numbers)
{
syscall_warn_user ();
- return NULL;
+ return false;
}

const char **
@@ -444,40 +445,27 @@ xml_list_of_syscalls (struct gdbarch *gdbarch)
}

/* Iterate over the syscall_group_desc element to return a list of
- syscalls that are part of the given group, terminated by an empty
- element. If the syscall group doesn't exist, return NULL. */
+ syscalls that are part of the given group. If the syscall group
+ doesn't exist, return false. */

-static struct syscall *
-xml_list_syscalls_by_group (struct gdbarch *gdbarch, const char *group)
+static bool
+xml_list_syscalls_by_group (struct gdbarch *gdbarch, const char *group,
+ std::vector<int> &syscalls)
{
struct syscalls_info *syscalls_info = gdbarch_syscalls_info (gdbarch);
struct syscall_group_desc *groupdesc;
- struct syscall *syscalls = NULL;
- int nsyscalls;
- int i;

if (syscalls_info == NULL)
- return NULL;
+ return false;

groupdesc = syscall_group_get_group_by_name (syscalls_info, group);
if (groupdesc == NULL)
- return NULL;
+ return false;

- nsyscalls = groupdesc->syscalls.size ();
- syscalls = (struct syscall*) xmalloc ((nsyscalls + 1)
- * sizeof (struct syscall));
+ for (const struct syscall_desc *sysdesc : groupdesc->syscalls)
+ syscalls.push_back (sysdesc->number);

- for (i = 0; i < groupdesc->syscalls.size (); i++)
- {
- syscalls[i].name = groupdesc->syscalls[i]->name.c_str ();
- syscalls[i].number = groupdesc->syscalls[i]->number;
- }
-
- /* Add final element marker. */
- syscalls[i].name = NULL;
- syscalls[i].number = 0;
-
- return syscalls;
+ return true;
}

/* Return a NULL terminated list of syscall groups or an empty list, if
@@ -542,12 +530,13 @@ get_syscall_names (struct gdbarch *gdbarch)

/* See comment in xml-syscall.h. */

-struct syscall *
-get_syscalls_by_group (struct gdbarch *gdbarch, const char *group)
+bool
+get_syscalls_by_group (struct gdbarch *gdbarch, const char *group,
+ std::vector<int> &syscall_numbers)
{
init_syscalls_info (gdbarch);

- return xml_list_syscalls_by_group (gdbarch, group);
+ return xml_list_syscalls_by_group (gdbarch, group, syscall_numbers);
}

/* See comment in xml-syscall.h. */
diff --git a/gdb/xml-syscall.h b/gdb/xml-syscall.h
index 4429d66400..2e76a9a97f 100644
--- a/gdb/xml-syscall.h
+++ b/gdb/xml-syscall.h
@@ -51,13 +51,11 @@ void get_syscall_by_name (struct gdbarch *gdbarch,
const char **get_syscall_names (struct gdbarch *gdbarch);

/* Function used to retrieve the list of syscalls of a given group in
- the system. Return a list of syscalls that are element of the
- group, terminated by an empty element. The list is malloc'ed
- and must be freed by the caller. If group doesn't exist, return
- NULL. */
+ the system. The syscall numbers are appended to SYSCALL_NUMBERS.
+ If the group doesn't exist, return false. */

-struct syscall *get_syscalls_by_group (struct gdbarch *gdbarch,
- const char *group);
+bool get_syscalls_by_group (struct gdbarch *gdbarch, const char *group,
+ std::vector<int> &syscall_numbers);

/* Function used to retrieve the list of syscall groups in the system.
Return an array of strings terminated by a NULL element. The list

--
2.18.0

John Baldwin

2018-11-09 20:04:31 UTC

When setting a syscall catchpoint by name, catch syscalls whose name
or alias matches the requested string.

When the ABI of a system call is changed in the FreeBSD kernel, this
is implemented by leaving a compatibility system call using the old
ABI at the existing "slot" and allocating a new system call for the
version using the new ABI. For example, new fields were added to the
'struct kevent' used by the kevent() system call in FreeBSD 12. The
previous kevent() system call in FreeBSD 12 kernels is now called
freebsd11_kevent() and is still used by older binaries compiled
against the older ABI. The freebsd11_kevent() system call can be
tagged with an "alias" attribute of "kevent" permitting 'catch syscall
kevent' to catch both system calls and providing the expected user
behavior for both old and new binaries. It also provides the expected
behavior if GDB is compiled on an older host (such as a FreeBSD 11
host).

gdb/ChangeLog:

* NEWS: Add entry documenting system call aliases.
* break-catch-syscall.c (catch_syscall_split_args): Pass 'result'
to get_syscalls_by_name.
* gdbarch.sh (UNKNOWN_SYSCALL): Remove.
* gdbarch.h: Regenerate.
* syscalls/gdb-syscalls.dtd (syscall): Add alias attribute.
* xml-syscall.c [!HAVE_LIBEXPAT] (get_syscalls_by_name): Rename
from get_syscall_by_name. Now accepts a reference to a vector of
integers and returns a bool.
[HAVE_LIBEXPAT] (struct syscall_desc): Add alias member.
(syscall_create_syscall_desc): Add alias parameter and pass it to
syscall_desc constructor.
(syscall_start_syscall): Handle alias attribute.
(syscall_attr): Add alias attribute.
(xml_get_syscalls_by_name): Rename from xml_get_syscall_number.
Now accepts a reference to a vector of integers and returns a
bool. Add syscalls whose alias or name matches the requested
name.
(get_syscalls_by_name): Rename from get_syscall_by_name. Now
accepts a reference to a vector of integers and returns a bool.
* xml-syscall.h (get_syscalls_by_name): Likewise.
---
gdb/ChangeLog | 24 ++++++++++++++
gdb/NEWS | 5 +++
gdb/break-catch-syscall.c | 11 ++-----
gdb/gdbarch.h | 3 --
gdb/gdbarch.sh | 3 --
gdb/syscalls/gdb-syscalls.dtd | 1 +
gdb/xml-syscall.c | 61 ++++++++++++++++++++---------------
gdb/xml-syscall.h | 10 +++---
8 files changed, 74 insertions(+), 44 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 81faa2994d..002ea3253c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,27 @@
+2018-11-09 John Baldwin <***@FreeBSD.org>
+
+ * NEWS: Add entry documenting system call aliases.
+ * break-catch-syscall.c (catch_syscall_split_args): Pass 'result'
+ to get_syscalls_by_name.
+ * gdbarch.sh (UNKNOWN_SYSCALL): Remove.
+ * gdbarch.h: Regenerate.
+ * syscalls/gdb-syscalls.dtd (syscall): Add alias attribute.
+ * xml-syscall.c [!HAVE_LIBEXPAT] (get_syscalls_by_name): Rename
+ from get_syscall_by_name. Now accepts a reference to a vector of
+ integers and returns a bool.
+ [HAVE_LIBEXPAT] (struct syscall_desc): Add alias member.
+ (syscall_create_syscall_desc): Add alias parameter and pass it to
+ syscall_desc constructor.
+ (syscall_start_syscall): Handle alias attribute.
+ (syscall_attr): Add alias attribute.
+ (xml_get_syscalls_by_name): Rename from xml_get_syscall_number.
+ Now accepts a reference to a vector of integers and returns a
+ bool. Add syscalls whose alias or name matches the requested
+ name.
+ (get_syscalls_by_name): Rename from get_syscall_by_name. Now
+ accepts a reference to a vector of integers and returns a bool.
+ * xml-syscall.h (get_syscalls_by_name): Likewise.
+
2018-11-09 John Baldwin <***@FreeBSD.org>

* break-catch-syscall.c (catch_syscall_split_args): Pass 'result'
diff --git a/gdb/NEWS b/gdb/NEWS
index ff9b192a38..ff225f361e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -38,6 +38,11 @@
requires the use of a keyword. Selecting a frame by level is
unchanged. The MI comment "-stack-select-frame" is unchanged.

+* System call catchpoints now support system call aliases. This is
+ used with the FreeBSD system call list so that system call
+ catchpoints will also trigger for legacy system call numbers used by
+ older FreeBSD binaries.
+
* New targets

NXP S12Z s12z-*-elf
diff --git a/gdb/break-catch-syscall.c b/gdb/break-catch-syscall.c
index f3740a1673..61c667a261 100644
--- a/gdb/break-catch-syscall.c
+++ b/gdb/break-catch-syscall.c
@@ -419,18 +419,13 @@ catch_syscall_split_args (const char *arg)
}
else
{
- /* We have a name. Let's check if it's valid and convert it
- to a number. */
- get_syscall_by_name (gdbarch, cur_name, &s);
-
- if (s.number == UNKNOWN_SYSCALL)
+ /* We have a name. Let's check if it's valid and fetch a
+ list of matching numbers. */
+ if (!get_syscalls_by_name (gdbarch, cur_name, result))
/* Here we have to issue an error instead of a warning,
because GDB cannot do anything useful if there's no
syscall number to be caught. */
error (_("Unknown syscall name '%s'."), cur_name);
-
- /* Ok, it's valid. */
- result.push_back (s.number);
}
}

diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 2cb6961083..8e354d2278 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -1569,9 +1569,6 @@ typedef ULONGEST (gdbarch_type_align_ftype) (struct gdbarch *gdbarch, struct typ
extern ULONGEST gdbarch_type_align (struct gdbarch *gdbarch, struct type *type);
extern void set_gdbarch_type_align (struct gdbarch *gdbarch, gdbarch_type_align_ftype *type_align);

-/* Definition for an unknown syscall, used basically in error-cases. */
-#define UNKNOWN_SYSCALL (-1)
-
extern struct gdbarch_tdep *gdbarch_tdep (struct gdbarch *gdbarch);

diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index bbfa8d2205..ff0e751f48 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -1393,9 +1393,6 @@ done
# close it off
cat <<EOF

-/* Definition for an unknown syscall, used basically in error-cases. */
-#define UNKNOWN_SYSCALL (-1)
-
extern struct gdbarch_tdep *gdbarch_tdep (struct gdbarch *gdbarch);

diff --git a/gdb/syscalls/gdb-syscalls.dtd b/gdb/syscalls/gdb-syscalls.dtd
index c2aa478aa4..6aa73f288a 100644
--- a/gdb/syscalls/gdb-syscalls.dtd
+++ b/gdb/syscalls/gdb-syscalls.dtd
@@ -12,4 +12,5 @@
<!ATTLIST syscall
name CDATA #REQUIRED
number CDATA #REQUIRED
+ alias CDATA #IMPLIED
groups CDATA #IMPLIED>
diff --git a/gdb/xml-syscall.c b/gdb/xml-syscall.c
index 664cee77dd..0e763045b4 100644
--- a/gdb/xml-syscall.c
+++ b/gdb/xml-syscall.c
@@ -61,13 +61,12 @@ get_syscall_by_number (struct gdbarch *gdbarch,
s->name = NULL;
}

-void
-get_syscall_by_name (struct gdbarch *gdbarch, const char *syscall_name,
- struct syscall *s)
+bool
+get_syscalls_by_name (struct gdbarch *gdbarch, const char *syscall_name,
+ std::vector<int> &syscall_numbers)
{
syscall_warn_user ();
- s->number = UNKNOWN_SYSCALL;
- s->name = syscall_name;
+ return false;
}

const char **
@@ -97,8 +96,8 @@ get_syscall_group_names (struct gdbarch *gdbarch)
/* Structure which describes a syscall. */
struct syscall_desc
{
- syscall_desc (int number_, std::string name_)
- : number (number_), name (name_)
+ syscall_desc (int number_, std::string name_, std::string alias_)
+ : number (number_), name (name_), alias (alias_)
{}

/* The syscall number. */
@@ -108,6 +107,10 @@ struct syscall_desc
/* The syscall name. */

std::string name;
+
+ /* An optional alias. */
+
+ std::string alias;
};

typedef std::unique_ptr<syscall_desc> syscall_desc_up;
@@ -207,10 +210,11 @@ syscall_group_add_syscall (struct syscalls_info *syscalls_info,

static void
syscall_create_syscall_desc (struct syscalls_info *syscalls_info,
- const char *name, int number,
+ const char *name, int number, const char *alias,
char *groups)
{
- syscall_desc *sysdesc = new syscall_desc (number, name);
+ syscall_desc *sysdesc = new syscall_desc (number, name,
+ alias != NULL ? alias : "");

syscalls_info->syscalls.emplace_back (sysdesc);

@@ -235,6 +239,7 @@ syscall_start_syscall (struct gdb_xml_parser *parser,
/* syscall info. */
char *name = NULL;
int number = 0;
+ char *alias = NULL;
char *groups = NULL;

for (const gdb_xml_value &attr : attributes)
@@ -243,6 +248,8 @@ syscall_start_syscall (struct gdb_xml_parser *parser,
name = (char *) attr.value.get ();
else if (strcmp (attr.name, "number") == 0)
number = * (ULONGEST *) attr.value.get ();
+ else if (strcmp (attr.name, "alias") == 0)
+ alias = (char *) attr.value.get ();
else if (strcmp (attr.name, "groups") == 0)
groups = (char *) attr.value.get ();
else
@@ -251,7 +258,8 @@ syscall_start_syscall (struct gdb_xml_parser *parser,
}

gdb_assert (name);
- syscall_create_syscall_desc (data->syscalls_info, name, number, groups);
+ syscall_create_syscall_desc (data->syscalls_info, name, number, alias,
+ groups);
}

@@ -259,6 +267,7 @@ syscall_start_syscall (struct gdb_xml_parser *parser,
static const struct gdb_xml_attribute syscall_attr[] = {
{ "number", GDB_XML_AF_NONE, gdb_xml_parse_attr_ulongest, NULL },
{ "name", GDB_XML_AF_NONE, NULL, NULL },
+ { "alias", GDB_XML_AF_OPTIONAL, NULL, NULL },
{ "groups", GDB_XML_AF_OPTIONAL, NULL, NULL },
{ NULL, GDB_XML_AF_NONE, NULL, NULL }
};
@@ -390,21 +399,22 @@ syscall_group_get_group_by_name (const struct syscalls_info *syscalls_info,
return NULL;
}

-static int
-xml_get_syscall_number (struct gdbarch *gdbarch,
- const char *syscall_name)
+static bool
+xml_get_syscalls_by_name (struct gdbarch *gdbarch, const char *syscall_name,
+ std::vector<int> &syscall_numbers)
{
struct syscalls_info *syscalls_info = gdbarch_syscalls_info (gdbarch);

- if (syscalls_info == NULL
- || syscall_name == NULL)
- return UNKNOWN_SYSCALL;
+ bool found = false;
+ if (syscalls_info != NULL && syscall_name != NULL)
+ for (const syscall_desc_up &sysdesc : syscalls_info->syscalls)
+ if (sysdesc->name == syscall_name || sysdesc->alias == syscall_name)
+ {
+ syscall_numbers.push_back (sysdesc->number);
+ found = true;
+ }

- for (const syscall_desc_up &sysdesc : syscalls_info->syscalls)
- if (sysdesc->name == syscall_name)
- return sysdesc->number;
-
- return UNKNOWN_SYSCALL;
+ return found;
}

static const char *
@@ -510,14 +520,13 @@ get_syscall_by_number (struct gdbarch *gdbarch,
s->name = xml_get_syscall_name (gdbarch, syscall_number);
}

-void
-get_syscall_by_name (struct gdbarch *gdbarch,
- const char *syscall_name, struct syscall *s)
+bool
+get_syscalls_by_name (struct gdbarch *gdbarch, const char *syscall_name,
+ std::vector<int> &syscall_numbers)
{
init_syscalls_info (gdbarch);

- s->number = xml_get_syscall_number (gdbarch, syscall_name);
- s->name = syscall_name;
+ return xml_get_syscalls_by_name (gdbarch, syscall_name, syscall_numbers);
}

const char **
diff --git a/gdb/xml-syscall.h b/gdb/xml-syscall.h
index 2e76a9a97f..a3b032aeb3 100644
--- a/gdb/xml-syscall.h
+++ b/gdb/xml-syscall.h
@@ -38,11 +38,13 @@ void set_xml_syscall_file_name (struct gdbarch *gdbarch,
void get_syscall_by_number (struct gdbarch *gdbarch,
int syscall_number, struct syscall *s);

-/* Function that retrieves the syscall number corresponding to the given
- name. It puts the requested information inside 'struct syscall'. */
+/* Function that retrieves the syscall numbers corresponding to the
+ given name. The numbers of all syscalls with either a name or
+ alias equal to SYSCALL_NAME are appended to SYSCALL_NUMBERS. If no
+ matching syscalls are found, return false. */

-void get_syscall_by_name (struct gdbarch *gdbarch,
- const char *syscall_name, struct syscall *s);
+bool get_syscalls_by_name (struct gdbarch *gdbarch, const char *syscall_name,
+ std::vector<int> &syscall_numbers);

/* Function used to retrieve the list of syscalls in the system. This list
is returned as an array of strings. Returns the list of syscalls in the

--
2.18.0

Eli Zaretskii

2018-11-09 20:18:02 UTC

Date: Fri, 9 Nov 2018 12:04:31 -0800
diff --git a/gdb/NEWS b/gdb/NEWS
index ff9b192a38..ff225f361e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -38,6 +38,11 @@
requires the use of a keyword. Selecting a frame by level is
unchanged. The MI comment "-stack-select-frame" is unchanged.
+* System call catchpoints now support system call aliases. This is
+ used with the FreeBSD system call list so that system call
+ catchpoints will also trigger for legacy system call numbers used by
+ older FreeBSD binaries.

IMO, this is very abstract and too vague to be useful. Since we won't
have anything more detailed in the manual, would it be possible to
make this description more concrete? E.g., how about using some of

Thanks.

John Baldwin

2018-11-16 17:43:56 UTC

Ok. I wasn't too happy with my first attempt either. I've tried to give
some more detail while not making it too long. Let me know what you think:

* System call catchpoints now support system call aliases on FreeBSD.
When the ABI of a system call changes in FreeBSD, this is
implemented by leaving a compatibility system call using the old ABI
at the existing number and allocating a new system call number for
the new ABI. For example, FreeBSD 12 altered the layout of 'struct
kevent' used by the 'kevent' system call. As a result, FreeBSD 12
kernels ship with both 'kevent' and 'freebsd11_kevent' system calls.
The 'freebsd11_kevent' system call is assigned an alias of 'kevent'
so that a system call catchpoint for the 'kevent' system call will
catch invocations of both the 'kevent' and 'freebsd11_kevent'
binaries. This ensures that 'kevent' system calls are caught for
binaries using either the old or new ABIs.

--
John Baldwin

Eli Zaretskii

2018-11-16 19:36:41 UTC

Date: Fri, 16 Nov 2018 09:43:56 -0800

Post by Eli Zaretskii
IMO, this is very abstract and too vague to be useful. Since we won't
have anything more detailed in the manual, would it be possible to
make this description more concrete? E.g., how about using some of

Ok. I wasn't too happy with my first attempt either. I've tried to give
* System call catchpoints now support system call aliases on FreeBSD.
When the ABI of a system call changes in FreeBSD, this is
implemented by leaving a compatibility system call using the old ABI
at the existing number and allocating a new system call number for
the new ABI. For example, FreeBSD 12 altered the layout of 'struct
kevent' used by the 'kevent' system call. As a result, FreeBSD 12
kernels ship with both 'kevent' and 'freebsd11_kevent' system calls.
The 'freebsd11_kevent' system call is assigned an alias of 'kevent'
so that a system call catchpoint for the 'kevent' system call will
catch invocations of both the 'kevent' and 'freebsd11_kevent'
binaries. This ensures that 'kevent' system calls are caught for
binaries using either the old or new ABIs.

LGTM, thanks.

Pedro Alves

2018-11-27 17:13:18 UTC

Should we, have something in the manual?

Thanks,
Pedro Alves

John Baldwin

2018-11-27 21:53:54 UTC

Should we, have something in the manual?

Hmm, here's a patch I came up with for the manual:

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 944a2c4383..ab4fad3c36 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -4683,6 +4683,22 @@ Catchpoint 2 (syscall 764)
(@value{GDBP})
@end smallexample

+On some operating systems, a system call name may map to more than one
+system call number. For example, the FreeBSD kernel allocates new
+system call numbers when changing the ABI of an existing system call.
+The kernel also includes a compatibility system call using the old ABI
+and number. FreeBSD's system call XML file includes aliases for
+compatibility system calls that are used to catch all versions of a
+system call. For example, FreeBSD 12 introduced a new variant of the
+@code{kevent} system call. Both system calls are caught when catching
+the @code{kevent} system call:
+
+@smallexample
+(@value{GDBP}) catch syscall kevent
+Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
+(@value{GDBP})
+@end smallexample
+
If you configure @value{GDBN} using the @samp{--without-expat} option,
it will not be able to display syscall names. Also, if your
architecture does not have an XML file describing its system calls,

--
John Baldwin

Eli Zaretskii

2018-11-28 06:31:42 UTC

Date: Tue, 27 Nov 2018 13:53:54 -0800
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 944a2c4383..ab4fad3c36 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -4683,6 +4683,22 @@ Catchpoint 2 (syscall 764)
@end smallexample
+On some operating systems, a system call name may map to more than one
+system call number. For example, the FreeBSD kernel allocates new
+system call numbers when changing the ABI of an existing system call.
+The kernel also includes a compatibility system call using the old ABI
+and number. FreeBSD's system call XML file includes aliases for
+compatibility system calls that are used to catch all versions of a
+system call. For example, FreeBSD 12 introduced a new variant of the
+
+Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])

This text is okay, but is it likely that any other OS will use this
facility? If not, we are better off describing it in the "Native"
section (adding a new subsection if needed), as a FreeBSD-only
feature.

Thanks.

Pedro Alves

2018-11-28 12:19:19 UTC

Post by John Baldwin
+On some operating systems, a system call name may map to more than one
+system call number. For example, the FreeBSD kernel allocates new
+system call numbers when changing the ABI of an existing system call.
+The kernel also includes a compatibility system call using the old ABI
+and number. FreeBSD's system call XML file includes aliases for
+compatibility system calls that are used to catch all versions of a
+system call. For example, FreeBSD 12 introduced a new variant of the
+
+Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
+

I'd suggest replacing "FreeBSD's system call XML file includes" with
something else that isn't so implementor-speak. Users needn't
be aware of the XML file. Maybe something along the lines of
"GDB is aware of aliases for compatibility system calls that
are used to catch ..." Or maybe remove the sentence altogether.
Maybe simplify it a bit further, as users don't really need
to be told that that's what FreeBSD does for all new syscalls,
just that some syscalls are like that. I think. Thus, something
like this is enough, IMHO:

On some operating systems, a system call name may map to more than one
system call number.

For example, FreeBSD 12 introduced a new variant of the @code{kevent} system
call, and included a compatibility system call using the old ABI and number.
As convenience, both system calls are caught when catching the @code{kevent}
system call by name:

@smallexample
(@value{GDBP}) catch syscall kevent
Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
(@value{GDBP})
@end smallexample

Thanks,
Pedro Alves

John Baldwin

2018-11-28 17:22:22 UTC

I'd suggest replacing "FreeBSD's system call XML file includes" with
something else that isn't so implementor-speak. Users needn't
be aware of the XML file. Maybe something along the lines of
"GDB is aware of aliases for compatibility system calls that
are used to catch ..." Or maybe remove the sentence altogether.
Maybe simplify it a bit further, as users don't really need
to be told that that's what FreeBSD does for all new syscalls,
just that some syscalls are like that. I think. Thus, something
On some operating systems, a system call name may map to more than one
system call number.
call, and included a compatibility system call using the old ABI and number.
@smallexample
Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
@end smallexample

Yes, I think this is better as well. Eli, I don't know if other OS's will
make use of this feature. Given Pedro's new text above, do you think it
should still be moved into a native section or should it stay in the the
syscall section?

--
John Baldwin

Eli Zaretskii

2018-11-28 17:44:19 UTC

Date: Wed, 28 Nov 2018 09:22:22 -0800
Yes, I think this is better as well. Eli, I don't know if other OS's will
make use of this feature. Given Pedro's new text above, do you think it
should still be moved into a native section or should it stay in the the
syscall section?

I question the need to make this text more general than this feature
will ever become. But if Pedro thinks we will have similar aliases on
other OSes, then sure, do it as Pedro suggests.

John Baldwin

2018-11-28 18:00:48 UTC

I question the need to make this text more general than this feature
will ever become. But if Pedro thinks we will have similar aliases on
other OSes, then sure, do it as Pedro suggests.

Oh, I was just referring to Pedro's version being shorter. I'm fine with
moving it. This is a bit longer as it restores a bit of the FreeBSD-specific
note about syscall ABIs but that seemed relevant when moving it:

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 944a2c4383..c60c2b80c4 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -22329,6 +22329,7 @@ configurations.
* Cygwin Native:: Features specific to the Cygwin port
* Hurd Native:: Features specific to @sc{gnu} Hurd
* Darwin:: Features specific to Darwin
+* FreeBSD:: Features specific to FreeBSD
@end menu

@node BSD libkvm Interface
@@ -23214,6 +23215,26 @@ better understand the cause of a fault. The default is off.
Show the current state of exceptions trapping.
@end table

+@node FreeBSD
+@subsection FreeBSD
+@cindex FreeBSD
+
+When the ABI of a system call is changed in the FreeBSD kernel, this
+is implemented by leaving a compatibility system call using the old
+ABI at the existing number and allocating a new system call number for
+the version using the new ABI. As a convenience, when a system call
+is caught by name, compatibility system calls are also caught.
+
+For example, FreeBSD 12 introduced a new variant of the @code{kevent}
+system call and catching the @code{kevent} system call by name catches
+both variants:
+
+@smallexample
+(@value{GDBP}) catch syscall kevent
+Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
+(@value{GDBP})
+@end smallexample
+

@node Embedded OS
@section Embedded Operating Systems

--
John Baldwin

Eli Zaretskii

2018-11-28 18:31:20 UTC

Date: Wed, 28 Nov 2018 10:00:48 -0800
Oh, I was just referring to Pedro's version being shorter. I'm fine with
moving it. This is a bit longer as it restores a bit of the FreeBSD-specific
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 944a2c4383..c60c2b80c4 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -22329,6 +22329,7 @@ configurations.
* Cygwin Native:: Features specific to the Cygwin port
* Darwin:: Features specific to Darwin
+* FreeBSD:: Features specific to FreeBSD
@end menu
@node BSD libkvm Interface
@@ -23214,6 +23215,26 @@ better understand the cause of a fault. The default is off.
Show the current state of exceptions trapping.
@end table
+
+When the ABI of a system call is changed in the FreeBSD kernel, this
+is implemented by leaving a compatibility system call using the old
+ABI at the existing number and allocating a new system call number for
+the version using the new ABI. As a convenience, when a system call
+is caught by name, compatibility system calls are also caught.
+
+
+Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])

This is fine with me, but let's hear what Pedro thinks.

Pedro Alves

2018-11-28 18:34:42 UTC

I question the need to make this text more general than this feature
will ever become. But if Pedro thinks we will have similar aliases on
other OSes, then sure, do it as Pedro suggests.

Don't other BSD kernels do something similar?

I think Linux always adds new syscalls under a new name, even if the
old replaced one is deprecated.

Post by John Baldwin
Oh, I was just referring to Pedro's version being shorter. I'm fine with
moving it. This is a bit longer as it restores a bit of the FreeBSD-specific

I'm fine with it as well. It just felt like if the we could keep it short, it'd
avoid fragmenting the information. IMO, a user reading the "catch syscall"
bits in the manual isn't going to remember to look up the FreeBSD-specific info
in a different node. Unless we add some xrefs.

Thanks,
Pedro Alves

John Baldwin

2018-11-28 19:14:57 UTC

I question the need to make this text more general than this feature
will ever become. But if Pedro thinks we will have similar aliases on
other OSes, then sure, do it as Pedro suggests.

Don't other BSD kernels do something similar?

Hmm, it is true that 4.4BSD itself included some compat system calls to handle
some ABI changes which is why the BSD's follow that model. NetBSD at least
follows FreeBSD's model of renaming old system calls and adding new numbers for
new ABIs. OpenBSD kind of does, but it retires older ABIs more aggressively
and seems to reuse old numbers unlike FreeBSD and NetBSD.

Post by Pedro Alves
I think Linux always adds new syscalls under a new name, even if the
old replaced one is deprecated.

Post by John Baldwin
Oh, I was just referring to Pedro's version being shorter. I'm fine with
moving it. This is a bit longer as it restores a bit of the FreeBSD-specific

Yes, that is why I started with it in the syscall section.

--
John Baldwin

Eli Zaretskii

2018-11-28 19:22:03 UTC

Date: Wed, 28 Nov 2018 18:34:42 +0000
IMO, a user reading the "catch syscall" bits in the manual isn't
going to remember to look up the FreeBSD-specific info in a
different node. Unless we add some xrefs.

Then let's add them.

John Baldwin

2018-11-09 20:04:32 UTC

Add a script to generate the FreeBSD XML system call table from the
sys/sys/syscall.h file in the kernel source tree. For ABI
compatiblity system calls used by older binaries (such as
freebsd11_kevent()), the original system call name is used as an
alias.

Run this script against the current syscall.h file in FreeBSD's head
branch which is expected to be the file used in 12.0 (head is
currently in code freeze as part of the 12.0 release process).

gdb/ChangeLog:

* syscalls/update-freebsd.sh: New file.
* syscalls/freebsd.xml: Regenerate.
---
gdb/ChangeLog | 5 ++
gdb/syscalls/freebsd.xml | 110 ++++++++++++++++++++++++++-------
gdb/syscalls/update-freebsd.sh | 78 +++++++++++++++++++++++
3 files changed, 170 insertions(+), 23 deletions(-)
create mode 100755 gdb/syscalls/update-freebsd.sh

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 002ea3253c..2f2b02d1c0 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-11-09 John Baldwin <***@FreeBSD.org>
+
+ * syscalls/update-freebsd.sh: New file.
+ * syscalls/freebsd.xml: Regenerate.
+
2018-11-09 John Baldwin <***@FreeBSD.org>

* NEWS: Add entry documenting system call aliases.
diff --git a/gdb/syscalls/freebsd.xml b/gdb/syscalls/freebsd.xml
index 810258a850..418a1ea838 100644
--- a/gdb/syscalls/freebsd.xml
+++ b/gdb/syscalls/freebsd.xml
@@ -1,4 +1,5 @@
-<?xml version="1.0"?>
+<?xml version="1.0"?> 
+

+
+
+
+<!DOCTYPE feature SYSTEM "gdb-syscalls.dtd">
+
+
+
+<syscalls_info>
+EOF
+
+awk '
+/MAXSYSCALL/ {
+ next
+}
+/^#define/ {
+ sub(/^SYS_/,"",$2);
+ printf " <syscall name=\"%s\" number=\"%s\"", $2, $3
+ if (sub(/^freebsd[0-9]*_/,"",$2) != 0)
+ printf " alias=\"%s\"", $2
+ printf "/>\n"
+}
+/\/\* [0-9]* is obsolete [a-z_]* \*\// {
+ printf " <syscall name=\"%s\" number=\"%s\"/>\n", $5, $2
+}
+/\/\* [0-9]* is freebsd[0-9]* [a-z_]* \*\// {
+ printf " <syscall name=\"%s_%s\" number=\"%s\" alias=\"%s\"/>\n", $4, $5, $2, $5
+}' $1 >> freebsd.xml.tmp
+
+cat >> freebsd.xml.tmp <<EOF
+</syscalls_info>
+EOF
+
+../../move-if-change freebsd.xml.tmp freebsd.xml

--
2.18.0

John Baldwin

2018-11-26 20:31:13 UTC

Post by John Baldwin
Relative to V2, this changes the "get syscalls" functions to pass in
an integer vector by reference to append syscall numbers to. It also
adds a NEWS entry and fixes some other nits noted by reviewers on the
V2 series.
Change get_syscalls_by_group to append to an existing vector of
integers.
Add an optional "alias" attribute to syscall entries.
Update the FreeBSD system call table to match FreeBSD 12.0.
gdb/ChangeLog | 41 ++++++++++++
gdb/NEWS | 5 ++
gdb/break-catch-syscall.c | 25 ++------
gdb/gdbarch.h | 3 -
gdb/gdbarch.sh | 3 -
gdb/syscalls/freebsd.xml | 110 ++++++++++++++++++++++++++-------
gdb/syscalls/gdb-syscalls.dtd | 1 +
gdb/syscalls/update-freebsd.sh | 78 +++++++++++++++++++++++
gdb/xml-syscall.c | 108 ++++++++++++++++----------------
gdb/xml-syscall.h | 20 +++---
10 files changed, 279 insertions(+), 115 deletions(-)
create mode 100755 gdb/syscalls/update-freebsd.sh

Ping? Eli signed off on an updated NEWS entry earlier in the thread. Any
further comments on the code changes?

--
John Baldwin

Pedro Alves

2018-11-27 17:19:56 UTC

Ping? Eli signed off on an updated NEWS entry earlier in the thread. Any
further comments on the code changes?

This looks good to me, though there's the issue with the non-const
references discussed here:

https://sourceware.org/ml/gdb-patches/2018-11/msg00351.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00441.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00443.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00444.html

Post by John Baldwin
- <syscall name="mknodat" number="498"/>
+ <syscall name="freebsd11_mknodat" number="498" alias="mknodat"/>
...
+ <syscall name="mknodat" number="559"/>

Does "catch syscall 498" catch only freebsd11_mknodat calls, or do
we for some reason end up catching calls to 559 as well?
I'd expect only 498. What about "catch syscall 559"?

Thanks,
Pedro Alves

John Baldwin

2018-11-27 20:00:18 UTC

Ping? Eli signed off on an updated NEWS entry earlier in the thread. Any
further comments on the code changes?

This looks good to me, though there's the issue with the non-const
https://sourceware.org/ml/gdb-patches/2018-11/msg00351.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00441.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00443.html
https://sourceware.org/ml/gdb-patches/2018-11/msg00444.html

Oh, whoops, I skimmed that thread I'm afraid. :(

I used a reference here due to the reasons you mentioned in your first
message, primarily not having to deal with it being NULL. I'm fine with
updating that to a pointer if that is the preferred route though.