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Message-ID: <194701d63f4e$c2a74770$47f5d650$@codeaurora.org> Date: Wed, 10 Jun 2020 12:44:14 -0500 From: <sidneym@...eaurora.org> To: <musl@...ts.openwall.com> Subject: RE: sigsetjmp > -----Original Message----- > From: Rich Felker <dalias@...c.org> > Sent: Monday, June 8, 2020 8:13 PM > To: sidneym@...eaurora.org > Cc: musl@...ts.openwall.com > Subject: Re: [musl] sigsetjmp > > On Mon, Jun 08, 2020 at 08:01:24PM -0500, sidneym@...eaurora.org wrote: > > > > > > > -----Original Message----- > > > From: Rich Felker <dalias@...c.org> > > > Sent: Monday, June 8, 2020 12:11 PM > > > To: sidneym@...eaurora.org > > > Cc: musl@...ts.openwall.com > > > Subject: Re: [musl] sigsetjmp > > > > > > On Sun, Jun 07, 2020 at 08:45:11PM -0500, sidneym@...eaurora.org > wrote: > > > > Wanting to make sure I'm reading the requirements correctly. > > > > > > > > Looks like this routine only needs to save the link register and > > > > env, call setjmp then restore the link register and env followed > > > > by the tail > > call. > > > > > > Yes, that's correct. This is an unconventional design but necessary > > > so > > that the > > > stack frame has already been restored when signals are unmasked by > > > siglongjmp. See the message for commit > > > 583e55122e767b1586286a0d9c35e2a4027998ab for a description of how > > > this works. > > > > > > > Hexagon was out of date so I did this: > > > > > > > > > > > > > > > > ..balign 4 > > > > > > > > ..type sigsetjmp,@function > > > > > > > > sigsetjmp: > > > > > > > > // if savemask is 0 sigsetjmp behaves like setjmp > > > > > > > > { > > > > > > > > p0 = cmp.eq(r1, #0) > > > > > > > > if (p0.new) jump:t ##setjmp > > > > > > > > } > > > > > > > > { > > > > > > > > memw(r0+#64+4) = r16 // save r16 in __ss[0] > > > > > > > > memw(r0+#64) = r31 // save linkregister in __fl > > > > > > > > r16 = r0 > > > > > > > > } > > > > > > This is not correct. __ss[0] is occupied by the saved signal mask, > > > and > > will be > > > clobbered when it's saved in the tail call. Instead you need to use > > > unused > > space > > > in struct __jmp_buf_tag. The canonical place is > > > (char*)__ss+8 (the "HURD ABI area" :) assuming _NSIG==65. > > > > I was not able to find a description of the HURD ABI area is it > > documented someplace? > > By "HURD ABI" I just mean the fact that sigset_t is gratuitously 128 bytes rather > than 8 bytes, because early glibc imagined uselessly having 1024 signals like > GNU HURD will someday do. > > The point is that only the first 8 (or 16, on MIPS*) bytes of the signal mask save > area (__ss[]) are actually used for saving a signal mask, and the rest is free for > sigsetjmp to use for other purposes. > > > So upon entry to sigsetjmp __ss[0] is holding the saved mask and using > > __ss[0] to buffer r16 will clobber it, correct? As it is coded > > __ss[0] is just used over the call to setjmp to preserve the value of r16. > > No, upon entry __ss[0] is uninitialized. __sigsetjmp_tail will store the signal > mask into it (and __ss[1], on 32-bit archs) before returning to the caller, and on > the second return (via siglongjmp) will restore the signal mask from there. > > > If __ss is r0+#64+4, then you are suggesting that I use r0+#64+4+8 or > > __ss[2]. I need to look into this some more because with that I'm have > > some testcase issues. > > Yes, that sounds right. Look what other archs do. The arm version is very easy > to read. Thanks, I updated the source to match aarch64 and at the moment all of the associated tests are passing. > > Rich
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