Re: [PATCH v3 2/3] Add an optional "alias" attribute to syscall entries.

[John Baldwin <jhb@FreeBSD.org>]

On 11/27/18 9:13 AM, Pedro Alves wrote:
> On 11/09/2018 08:18 PM, Eli Zaretskii wrote:
>>> From: John Baldwin <jhb@FreeBSD.org>
>>> 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
>> the text and examples you used in your description of the issue:
> 
> 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