Re: [Tinycc-devel] Problem using alloca

[Thomas Preud'homme]

Le mardi 01 juillet 2014 10:20:12, vous avez écrit :
> Yes. Please. You can tell me the steps for be able of send commits ?

Sure but first let's discuss how to make the patch.

1) Downloading the latest development code

So first you'll need a copy of the latest code that we keep in git source code 
management tool. You can find an installer for git at [1]. Once installed, 
you'll have two programs you can use: git-bash and git-gui if I remember 
correctly.

[1] http://git-scm.com/download/

Launch git-bash and there just type: git clone git://repo.or.cz/tinycc.git

This will create a directory "tinycc" in which you'll find the most recent 
code.

2) Hacking

From there, you'll have to take a look at lib/alloca86_64.S and 
lib/alloca86.S. You'll notice a "cmp $4096,%rax" or "cmp $4096,%eax" whose 
goal is to compare the parameter given to alloca (rounded up to a multiple of 
16) with 4096. If it's less or equal it will continue at p2 and skip the code 
you see below. Otherwise it'll allocate 4096 bytes by substracting this amount 
to the stack pointer (esp) and then read something on the stack (the test 
instruction) and loop again at the cmp instruction.

Basically it does a loop allocating 4096 bytes at a time and trying to read 
one of these byte before continuing the loop. If there is something to do when 
allocating 8MB or more, you'll have to add another cmp just before the p1 
label to compare eax with this value and then do what needs to be done on 
Windows. For this I cannot tell, you seem to know more than me.

3) Committing in the main repo

Once the patch written, you will prepare the file for the commit with git add 
lib/alloca86.S lib/alloca86_64.S. Then you should inspect it with "git diff --
cached" to make sure you didn't add spurious whitespace somewhere (it will 
appear in red in git). Then if all is ok you can commit with "git commit" and 
enter the commit message. At this stage you have a local commit, meaning that 
only you have this commit, nobody else has it. You'll need to "push" this 
commit to the main repository for everybody to see it. This is done by doing a 
"git push ssh://address@hidden/srv/git/tinycc.git mob:mob" that instruct to 
push everything you made on branch mob (the one automatically created when you 
issued "git clone" initially) on a branch mob on our main repo.

If you have an error message it means somebody else pushed some commits to the 
main repo. In this case, just do "git pull --rebase" and then you'll be able 
to do the push. If there is any problem, feel free to ask here, I'm sure 
you'll find an answer to your question. Note that this answer will not come 
from me as I'll be absent for two weeks from this friday.

I look forward to your contribution.

Best regards,

Thomas

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