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From: | Herman ten Brugge |
Subject: | Re: [Tinycc-devel] bounds checking with tcc |
Date: | Mon, 2 Dec 2019 18:24:27 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 |
Hello, I did some debugging with bouds-checking and came up with attached patch. I seriously doubt any one did use bounds checking in a large project before.Currently I can use this now in a large multi threaded project. It still needs some more testing so do not apply the patch yet.
I disabled some errors. For example if a bounded pointer is not found I give no error. I also relaxed printing free errors. There were some off by 1 errors in lib/bcheck.c and I needed to make the code thread safe. I used the patch to not link in libtcc1.a in shared objects when bounds checking so I have only one memory pool. This has to be documented because you cannot use this with dlopen for example. I also added the pthread library when bounds checking so it is now multi threaded.
I found another problem with nocode_wanted when using sizeof().Also the push/pop trick needed to push some more registers when more parameters are passed in registers.
I probably forget to mention a lot a other changes. See the patch.I only tested this on linux x86_64. There are for sure problems on other targets.
Regards, Herman On 2019-11-28 17:41, Michael Matz wrote:
Hello again, but to maybe be a bit more constructive: On Thu, 28 Nov 2019, Michael Matz wrote:I fixed this with some push/pop trickery.I see, yeah, expanding calls during calls is broken as gfunc_call in the generators doesn't generally leave a trace in vtop[] which registers are currently holding values. I think you only need so push/pop si/di, as cx/dx aren't used intentionally during reg-param setup. (I think i386-gen.c has a simila bug with fastcall functions).This probably could be improved. I have now added a minimum patch so bounds checking works a little bit. We need still to fix the shared lib reloc problems and the malloc/free hooks.Do we? Can we perhaps also simply declare bounds checking to work only with the main executable? Or remove that whole feature altogether?And perhaps another compromise: only conditionally enable tracking of locals: Invent a new cmdline option (say, '-bb'), which sets do_bounds_checking to 2. And only if it's > 1 you would also track locals, whereas with == 1 you would only track arrays and structs. Your decision, I think you can push this patch either with that change, or without (but try to remove cx/dx from the push/pop). It doesn't make tccs source code larger or uglier in any meaningful way, but does fix practical bugs. Ciao, Michael.
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