Date: Mon, 3 Jan 2022 09:37:00 +0800 From: Sebastien Bourdeauducq <sb@...abs.hk> To: musl@...ts.openwall.com Subject: Re: building statically linked DSOs with musl On 1/1/22 20:56, Joakim Sindholt wrote: > Musl will set up its own internal global libc structure > with a bunch of values during the initial dynamic loading phase; among > the members is libc.auxv, which is what __vdsosym will look through when > trying to find the VDSO. Since you never ran musl's dynamic linker (and > even if your host binary was musl-based, not the one that would have > initialized the libc.auxv baked in to your statically linked DSO) it > won't have set up this and a whole host of other things. Thanks for the hint. libc.auxv seems to be set up by __dls2b, which itself is called by __dls2 via find_sym(&ldso, "__dls2b", 0). How does this code work when a program is statically linked against musl? On 1/3/22 05:41, Markus Wichmann wrote: > There can be different heaps, but not different brk heaps. Basically, > brk() manages a global variable generated by the kernel. You can work > around that problem by installing a seccomp filter that makes brk() > always fail, forcing the allocators to fall back to mmap(). mimalloc exclusively uses mmap() already, so that will be OK and will not require a workaround. It shouldn't matter if the other allocator uses brk(). > The thread pointer does not match up, Seems it does (okay, probably by accident): https://git.musl-libc.org/cgit/musl/tree/arch/x86_64/pthread_arch.h?id=cfdfd5ea3ce14c6abf7fb22a531f3d99518b5a1b#n4 https://github.com/bminor/glibc/blob/b92a49359f33a461db080a33940d73f47c756126/sysdeps/x86/nptl/thread_pointer.h#L30 > and so no functions accessing the thread pointers will work. That > includes functions that read the current thread pointer, so you cannot > know in advance which those are. All the implementation-defined > structures mismatch, so none of the locking functions work, and neither > do the semaphore functions. AFAIK I would not need to share locks or semaphores across the plugin. I need to see if the rest of this thread business has other consequences. Sébastien
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