Date: Wed, 27 Apr 2016 22:07:51 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH v2] add powerpc64 port On Wed, Apr 27, 2016 at 08:38:19PM -0500, Bobby Bingham wrote: > > > @@ -141 +141 @@ > > > -mcontext_t: mcontext_t, mcontext_t*, size (*) , align (*)  > > > +mcontext_t: sigcontext, sigcontext*, size (*) , align (*)  > > > > IIRC on other archs we made an effort to make the tag here match ABI > > (duplicating the struct def if needed). Not sure if it matters. > > I can duplicate the structure if you want. But it looks like glibc used > to do 'typedef struct sigcontext mcontext_t' as well: > > https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h;h=a499a80ef9994e541b866202ee8440843b004fdd;hp=b75e25a3c84c852b22e1690ff530d3ddb8dff257;hb=5ef6ae4bdb;hpb=39b04aa39823faf1cc414e7f3eca4f43e01426e4 Wow, the glibc stuff is an utter mess and grossly non-conforming. It doesn't even have a uc_mcontext member of type mcontext_t. At least it looks like all modern kernels have the mcontext_t at the end where it's extensible and doesn't break access to uc_sigmask if it changes. We should probably check and make sure both the current 32-bit powerpc ucontext_t and your proposed powerpc64 one have the mcontext_t members (at least the program counter) accessible at the expected locations. We should probably also let the kernel people know that mcontext_t (and its location) are ABI whether they like it or not. This is imposed by POSIX and the glibc hack of making it a pointer is non-conforming. > > > @@ -195 +195 @@ > > > -sem_t: sem_t, sem_t*, size (*) , align (*)  > > > +sem_t: sem_t, sem_t*, size (*) , align (*)  > > > > > @@ -229,2 +229,2 @@ > > > -cmsghdr: cmsghdr, cmsghdr*, size (*) , align (*)  > > > +cmsghdr: cmsghdr, cmsghdr*, size (*) , align (*)  > > > > This is likely going to hit the same issue we're trying to debug on > > mips64. > > The mips64 issue ended up not being alignment related. Do you still > want me to do something about this? And if so, do you have a suggestion? I'm not entirely sure, but I think you can leave it alone for now. If it needs fixing here, then it already does on multiple existing archs, and they should be handled together. > > > @@ -416 +417 @@ > > > -ucontext_t: ucontext, ucontext*, size (*) , align (*)  > > > +ucontext_t: ucontext, ucontext*, size (*) , align (*)  > > > > This may be a real problem. ucontext_t is ABI between kernel and > > userspace and if it's wrong cancellation won't work right. > > Kernel commit ce48b2100785 expanded the vmx_reserve member of mcontext_t > by 256 bytes. The glibc headers haven't been updated for this expansion. Ah. As noted above, uc_mcontext is at the end so it shouldn't break anything. Rich
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