Date: Thu, 01 Aug 2013 08:05:01 +0200 From: Luca Barbato <lu_zero@...too.org> To: musl@...ts.openwall.com Subject: Re: Solving the recursive memcpy/memset/etc. issue On 01/08/13 02:49, Rich Felker wrote: > OK, so now that it's hit us for real, what should we do about GCC > generating code for memcpy, memset, etc. which might contain infinite > recursion? Aside from the ARM issue (which was separate), we know the > option causing this bad code generation, and it can be disabled via > -fno-tree-loop-distribute-patterns. However, if GCC policy is that > they consider the compiler entitled to generate calls to > memcpy/memset/memmove/memcmp whenever it wants, then we're just going > to be playing whack-a-mole. Sounds lovely. > The only fully viable option I see is replacing the code for these > functions with code that uses volatile objects so as to make > optimization utterly impossible. This will of course make them > incredibly slow, but at least we would have safe, working C code, and > we could add asm for each supported arch. Not exactly great. > An alternative might be to test the compiler in configure to determine > if, with the selected CFLAGS, it generates recursive code for these > functions, and if so, defining a macro that causes musl to revert to > the volatile code. Sounds much better. > Other ideas? For now, if -fno-tree-loop-distribute-patterns fixes it > (still waiting on confirmation for this) I'm going to commit that to > configure, but it doesn't seem like a viable long-term solution. I'd rather check and error out reporting the compiler is broken. Then have an explicit configure option to try to workaround it. > My ideal outcome would be a promise from the GCC developers that, in > future GCC versions, -ffreestanding implies disabling any options > which would generate calls to the mem* functions. However that sounds > unlikely. They have competition, if clang works better then we could just suggest to use it and nowadays gcc has no deployment advantage to it anymore. lu
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