Re: [PATCH] gdb: fix -Wdeprecated-declarations on macOS

[Simon Marchi <simark@simark.ca>]

On 3/28/23 11:10, John Baldwin wrote:
> On 3/28/23 7:55 AM, Simon Marchi via Gdb-patches wrote:
>> On 3/28/23 10:16, Enze Li via Gdb-patches wrote:
>>> I noticed that there are some issues when compiling on macOS.  There are
>>> a few places where errors like the following are reported,
>>>
>>> ======
>>>    CXX    cli/cli-cmds.o
>>> cli/cli-cmds.c:929:14: error: 'vfork' is deprecated: Use posix_spawn or fork [-Werror,-Wdeprecated-declarations]
>>>    if ((pid = vfork ()) == 0)
>>>               ^
>>> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:604:1: note: 'vfork' has been explicitly marked deprecated here
>>> __deprecated_msg("Use posix_spawn or fork")
>>> ^
>>> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h:208:48: note: expanded from macro '__deprecated_msg'
>>>          #define __deprecated_msg(_msg) __attribute__((__deprecated__(_msg)))
>>>                                                        ^
>>> 1 error generated.
>>> ======
>>>
>>> This patch is only available for the macOS platform.  This is done by
>>> using macros to differentiate between specific platforms.
>>>
>>> Tested by rebuilding both on x86_64 linux and macOS Big Sur.
>>
>> Any idea why vfork is deprecated on macOS?  I can't find any answer
>> online.
>>
>> I think it would be good to have a gdb_ util function with the ifdef at
>> a single place, with an appropriate comment.  I don't know how to call
>> this function though.  Would calling it gdb_vfork be misleading, because
>> it won't always vfork?
> 
> Even if vfork is deprecated, you still want to use it instead of fork I think
> as long as it exists.  The real fix is to add a patch to use posix_spawn
> to fork the shell instead of vfork when posix_spawn exists.  posix_spawn is
> just a wrapper around vfork + execve on FreeBSD's libc for example (I haven't
> looked to see what it is on Linux but suspect it is similar).

I guess that using posix_spawn would require some very significant
architectural changes?  Right now, we fork (or vfork), do some cleanup /
prep work, and then exec.  How do you do that with posix_spawn?

Simon