Re: [PATCH v2 1/1] config: work around bug with includeif:onbranch and early config

From: Jeff Hostetler <git@jeffhostetler.com>
Date: Aug 1, 2019, 17:24 UTC
Message-ID: <7f4257d3-5ae0-3a83-84f1-bee83682fa36@jeffhostetler.com>
In-Reply-To: <20190801004928.GA6351@sigill.intra.peff.net>

On 7/31/2019 8:49 PM, Jeff King wrote:

Show 37 quoted lines

> On Wed, Jul 31, 2019 at 07:12:57PM -0400, Jeff King wrote:
> 
>> Hrm. But common-main calls initialize_the_repository(), which points it
>> at &the_repo. And I can't find any other assignments. So how does it
>> become NULL? And is every caller of have_git_dir() at risk of
>> segfaulting?
>>
>> Ah, I see. I think it is that trace2 reads the configuration very early.
>> I think we ought to do this:
>>
>> diff --git a/common-main.c b/common-main.c
>> index 582a7b1886..89fd415e55 100644
>> --- a/common-main.c
>> +++ b/common-main.c
>> @@ -39,14 +39,14 @@ int main(int argc, const char **argv)
>>   
>>   	git_resolve_executable_dir(argv[0]);
>>   
>> +	initialize_the_repository();
>> +
>>   	trace2_initialize();
>>   	trace2_cmd_start(argv);
>>   	trace2_collect_process_info(TRACE2_PROCESS_INFO_STARTUP);
>>   
>>   	git_setup_gettext();
>>   
>> -	initialize_the_repository();
>> -
>>   	attr_start();
>>   
>>   	result = cmd_main(argc, argv);
> 
> By the way, I wondered why trace2's existing config reading did not
> cause us to segfault because of this. It is because it invented the
> "very early config" function which always ignores some config sources
> (working around this problem, but also making it weirdly unlike most
> other config).

Yes, I added the "very early config" to try to work around some of the chicken-n-egg problems. I can't say that I was completely happy with having to do that. I haven't had time to play with your patch suggestion here, but I think it would be fine to do if it will help with the original problem.

In [1] I added code to just start the clock in isolation (rather than being part of the trace2_initialize() -- which does all the config loading and subsystem initialization). So it is OK to let the trace2_initialize() run a little later. (Part of the reason for that split was to allow git_resolve_executable_dir() to run first, since that data was needed to find the location of the system config relative to the exe path (sigh).)

[1] a089724958a trace2: refactor setting process starting time

So, as you suggested in your previous response, something like this would/should be fine.

$ git diff

diff --git a/common-main.c b/common-main.c
index 582a7b1886..71e21dd20a 100644
--- a/common-main.c
+++ b/common-main.c
@@ -39,16 +39,16 @@ int main(int argc, const char **argv)

         git_resolve_executable_dir(argv[0]);

-       trace2_initialize();
-       trace2_cmd_start(argv);
-       trace2_collect_process_info(TRACE2_PROCESS_INFO_STARTUP);
-
         git_setup_gettext();

         initialize_the_repository();

         attr_start();

+       trace2_initialize();
+       trace2_cmd_start(argv);
+       trace2_collect_process_info(TRACE2_PROCESS_INFO_STARTUP);
+
         result = cmd_main(argc, argv);

         trace2_cmd_exit(result);