Good catch! I'll commit the change tonight. - Justin
On Tue, Feb 2, 2016 at 3:48 AM, Mark Millard <mar...@dsl-only.net> wrote: > I tried the change to -32 and 32 (from -20 and 20) on/for the powerpc > (32-bit) PowerMac that I use and the results were: > > A) "info frame" in gdb shows signal handlers are now started with 16-byte > aligned stack frames. (Applies to gcc 4.2.1 based contexts too, not just to > the clang 3.8.0 ones with the __vfprintf-tied segmentation faults during > signals.) > > and. . . > > B) The "clang 3.8.0 compiled __vfprintf" segmentation faults in libc/stdio > library code during signal handlers that use such code no longer happen > because the alignment matches the code requirements. > > I've added this information to Bug 206810. > > > (Note: There are a couple of segmentation fault contexts that I've never tied > down to any specific property: no discovered evidence of signal handler > involvement or of __vfprintf involvement, for example. These are still a > problem. But where I had tied the faults to signal handlers using __vfprintf > now instead work fine in my experimental clang 3.8.0 based builds.) > > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Feb-1, at 12:11 AM, Mark Millard <markmi at dsl-only.net> wrote: > > The -16/16 code below produced correct alignment but too little space. > > The -20/20 code below produces enough space but misalignment. > > To maintain 16-byte alignment while increasing the space would have required > going from -16/16 to -32/32. At least that is how I understand this code. > > >> Index: sys/powerpc/powerpc/sigcode32.S >> =================================================================== >> --- sys/powerpc/powerpc/sigcode32.S >> (.../head/sys/powerpc/powerpc/sigcode32.S) (revision 209975) >> +++ sys/powerpc/powerpc/sigcode32.S >> (.../projects/clang380-import/sys/powerpc/powerpc/sigcode32.S) (working >> copy) >> @@ -45,9 +45,9 @@ >> */ >> .globl CNAME(sigcode32),CNAME(szsigcode32) >> CNAME(sigcode32): >> - addi 1,1,-16 /* reserved space for callee */ >> + addi 1,1,-20 /* reserved space for callee */ >> blrl >> - addi 3,1,16+SF_UC /* restore sp, and get &frame->sf_uc >> */ >> + addi 3,1,20+SF_UC /* restore sp, and get &frame->sf_uc >> */ >> li 0,SYS_sigreturn >> sc /* sigreturn(scp) */ >> li 0,SYS_exit > > > > The "working copy" is -r266778 from 2014-May-27. > > -r209975 is from 2010-Jul-13. > > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Jan-31, at 10:58 PM, Mark Millard <markmi at dsl-only.net> wrote: > > Just a correction to a sentence that I wrote. I had written: > >> Frame at: 0x...90 vs. 0x...1c >> call by frame: 0x...b0 vs. 0x...1c >> Arglist at: 0x...70 vs. 0x...dc >> Locals at: 0x...70 vs. 0x...dc >> Previous frame's sp: 0x...90 vs. 0x...1c >> >> It looks like 4 additional pad bytes on the user/process stack are needed to >> get back to alignment. > > Of course the figures on the right need to get smaller, not larger: The stack > grows towards smaller addresses. So to get to 0x...0 on the right I should > have said: > > It looks like 12 additional pad bytes on the user/process stack are needed to > get back to alignment. > > That would produce: > > Frame at: 0x...90 vs. 0x...10 > call by frame: 0x...b0 vs. 0x...10 > Arglist at: 0x...70 vs. 0x...d0 > Locals at: 0x...70 vs. 0x...d0 > Previous frame's sp: 0x...90 vs. 0x...10 > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Jan-31, at 10:47 PM, Mark Millard <markmi at dsl-only.net> wrote: > > More evidence: By adding "break raise" and then using "info frame" to show > the alignment at that point I can show that the later signal delivery changes > the alignment on the user process stack compared to when raise was called. > (Later I show the same for thr_kill.) > >> Breakpoint 2, __raise (s=29) at /usr/src/lib/libc/gen/raise.c:50 >> warning: Source file is more recent than executable. >> 50 if (__sys_thr_self(&id) == -1) >> (gdb) info frame >> Stack level 0, frame at 0xffffdc90: >> pc = 0x41904630 in __raise (/usr/src/lib/libc/gen/raise.c:50); saved pc = >> 0x1800774 >> called by frame at 0xffffdcb0 >> source language c. >> Arglist at 0xffffdc70, args: s=29 >> Locals at 0xffffdc70, Previous frame's sp is 0xffffdc90 >> Saved registers: >> r29 at 0xffffdc84, r30 at 0xffffdc88, r31 at 0xffffdc8c, pc at 0xffffdc94, >> lr at 0xffffdc94 >> (gdb) cont >> Continuing. >> >> Program received signal SIGINFO, Information request. >> >> Breakpoint 1, 0x018006d0 in handler () >> (gdb) info frame >> Stack level 0, frame at 0xffffd71c: >> pc = 0x18006d0 in handler; saved pc = 0xffffe008 >> called by frame at 0xffffd71c >> Arglist at 0xffffd6dc, args: >> Locals at 0xffffd6dc, Previous frame's sp is 0xffffd71c >> Saved registers: >> r31 at 0xffffd718, pc at 0xffffd720, lr at 0xffffd720 > > Note the difference (raise before delivery vs. handler via delivery): > > Frame at: 0x...90 vs. 0x...1c > call by frame: 0x...b0 vs. 0x...1c > Arglist at: 0x...70 vs. 0x...dc > Locals at: 0x...70 vs. 0x...dc > Previous frame's sp: 0x...90 vs. 0x...1c > > It looks like 4 additional pad bytes on the user/process stack are needed to > get back to alignment. > > [The span of addresses seems to be about: 0xffffdc90-0xffffd6dc==0x5B4==1460 > (raise's "frame at" minus handler's "Locals at").] > > > If I look at the frame for "break thr_kill" it also still shows an aligned > user/process stack before the delivery: > >> Breakpoint 3, 0x419046a0 in thr_kill () from /lib/libc.so.7 >> (gdb) info frame >> Stack level 0, frame at 0xffffdc70: >> pc = 0x419046a0 in thr_kill; saved pc = 0x41904650 >> called by frame at 0xffffdc90 >> Arglist at 0xffffdc70, args: >> Locals at 0xffffdc70, Previous frame's sp is 0xffffdc70 > > (The relevant addresses are the same as raise showed.) > > > Reminder of the source program structure that uses the potentially > frame/stack alignment sensitive libc/stdio library code: > >> # more sig_snprintf_use_test.c >> #include <signal.h> // for signal, SIGINFO, SIG_ERR, raise. >> #include <stdio.h> // for snprintf >> >> void handler(int sig) >> { >> char buf[32]; >> snprintf(buf, sizeof buf, "%d", sig); // FreeBSD's world does such >> // things in some of its handlers. >> } >> >> int main(void) >> { >> handler(0); // handler gets aligned stack frame for this; snprintf works >> here. >> if (signal(SIGINFO, handler) != SIG_ERR) raise(SIGINFO); >> // raise gets aligned stack frame; >> // handler gets misaligned stack frame; >> // >> snprintf/__vfrpintf/io_flush/__sfvwrite/memcpy: >> // when built by clang 3.8.0 are sensitive to >> // the misalignment. >> return 0; >> } > > > > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Jan-31, at 9:12 PM, Mark Millard <markmi at dsl-only.net> wrote: > > A summary of the later finding details for what I've done so far: > > It is system library code (__vfprintf and its inline io_flush call to > __sfvwrite) that may produce and use a potentially bad &iop->uio address, > depending the mix of how the calculation works and the stack/frame alignment > present in signal delivery. The gcc 4.2.1 vs. clang 3.8.0 program status > makes no difference to if it ends up with a segmentation fault or not. > > When __vfprintf and its inline io_flush call to __sfvwrite is compiled by gcc > 4.2.1 --which always uses addition for offsets, voiding alignment > assumptions-- no variant of the program gets a segmentation fault. gcc 4.2.1 > does not create the dependency on the alignment that clang 3.8.0 does. Yet > the misalignment is present. (See the details.) > > When clang3.8.0 compiles __vfprintf and its inline io_flush call to > __sfvwrite --which uses masking for the offset in calculating &iop->uio, > making alignment assumptions-- every variant of the program gets a > segmentation fault. (The misalignment is still present.) > > > > The details for the misalignment evidence follow. > > For (C) "on a pure gcc 4.2.1 buildworld/buildkernel system". . . > > C0) For gcc421-a.out gets signal delivery to its handler: "info frame" in > this (C) context: > > This *has* a misaligned signal delivery stack but there is no segmentation > fault. > >> Program received signal SIGINFO, Information request. >> >> Breakpoint 1, 0x018006e0 in handler () >> (gdb) bt >> #0 0x018006e0 in handler () >> #1 <signal handler called> >> #2 0x00000000 in ?? () >> (gdb) info frame >> Stack level 0, frame at 0xffffd73c: >> pc = 0x18006e0 in handler; saved pc = 0xffffe008 >> called by frame at 0xffffd73c >> Arglist at 0xffffd6fc, args: >> Locals at 0xffffd6fc, Previous frame's sp is 0xffffd73c >> Saved registers: >> r31 at 0xffffd738, pc at 0xffffd740, lr at 0xffffd740 > > > So misaligned (multiple of 4 but of no higher power of 2) for "frame at", > "called by frame at" (which is listed as the same as "frame at"), "Arglist", > "Locals", and "Previous frame's sp" (which is listed as the same as "frame > at"). > > In this case I also list __vfprintf's misalignment evidence for reference: > (break __vfprintf used.) > >> (gdb) info frame >> Stack level 0, frame at 0xffffd57c: >> pc = 0x41930af8 in __vfprintf (/usr/src/lib/libc/stdio/vfprintf.c:452); >> saved pc = 0x41992e18 >> called by frame at 0xffffd6fc >> source language c. >> Arglist at 0xffffd29c, args: fp=0xffffd5dc, locale=0x419c41e0 >> <__xlocale_global_locale>, fmt0=0x1800a1c "%d", ap=0xffffd6cc >> Locals at 0xffffd29c, Previous frame's sp is 0xffffd57c >> Saved registers: >> r30 at 0xffffd574, r31 at 0xffffd578, pc at 0xffffd580, lr at 0xffffd580 > > > So misaligned (multiple of 4 but of no higher power of 2) for "frame at", > "called by frame at", "Arglist", "Locals", and "Previous frame's sp" (which > is listed as the same as "frame at"). > > Just to have one for reference, here is the "info frame" for the direct > handler call --which gets a properly aligned frame/stack: > >> (gdb) info frame >> Stack level 0, frame at 0xffffdcc0: >> pc = 0x18006e0 in handler; saved pc = 0x1800734 >> called by frame at 0xffffdcd0 >> Arglist at 0xffffdc80, args: >> Locals at 0xffffdc80, Previous frame's sp is 0xffffdcc0 >> Saved registers: >> r31 at 0xffffdcbc, pc at 0xffffdcc4, lr at 0xffffdcc4 > > Only the signal delivery is creating non-aligned stack frames. > > > C1) For clang380-a.out gets signal delivery to its handler: "info frame" in > this (C) context: > > This *has* a misaligned signal delivery stack but there is no segmentation > fault. > >> (gdb) info frame >> Stack level 0, frame at 0xffffd70c: >> pc = 0x18006d0 in handler; saved pc = 0xffffe008 >> called by frame at 0xffffd70c >> Arglist at 0xffffd6cc, args: >> Locals at 0xffffd6cc, Previous frame's sp is 0xffffd70c >> Saved registers: >> r31 at 0xffffd708, pc at 0xffffd710, lr at 0xffffd710 > > So misaligned (multiple of 4 but of no higher power of 2) for "frame at", > "called by frame at", "Arglist", "Locals", and "Previous frame's sp" (which > is listed as the same as "frame at"). > > > > For (B) "on a clang 3.8.0 buildworld and gcc 4.2.1 buildkernel mix". . . > > B0) For gcc421-a.out gets signal delivery to its handler: "info frame" in > this (B) context: > > This *has* a misaligned signal delivery stack and there *is* a segmentation > fault. > >> Program received signal SIGINFO, Information request. >> >> Breakpoint 1, 0x018006e0 in handler () >> (gdb) bt >> #0 0x018006e0 in handler () >> #1 <signal handler called> >> #2 0x00000000 in ?? () >> (gdb) info frame >> Stack level 0, frame at 0xffffd74c: >> pc = 0x18006e0 in handler; saved pc = 0xffffe008 >> called by frame at 0xffffd74c >> Arglist at 0xffffd70c, args: >> Locals at 0xffffd70c, Previous frame's sp is 0xffffd74c >> Saved registers: >> r31 at 0xffffd748, pc at 0xffffd750, lr at 0xffffd750 >> (gdb) cont >> Continuing. >> >> Program received signal SIGSEGV, Segmentation fault. >> 0x419a89c8 in memcpy (dst0=0xffffd714, src0=<optimized out>, >> length=<optimized out>) at /usr/src/lib/libc/string/bcopy.c:124 >> warning: Source file is more recent than executable. >> 124 TLOOP1(*--dst = *--src); > > > > B1) For clang380-a.out gets signal delivery to its handler: "info frame" in > this (B) context: > (i.e., what I originally reported on and submitted a Bug report for) > > This *has* a misaligned signal delivery stack and there *is* a segmentation > fault. > >> Program received signal SIGINFO, Information request. >> >> Breakpoint 1, 0x018006d0 in handler () >> (gdb) info frame >> Stack level 0, frame at 0xffffd71c: >> pc = 0x18006d0 in handler; saved pc = 0xffffe008 >> called by frame at 0xffffd71c >> Arglist at 0xffffd6dc, args: >> Locals at 0xffffd6dc, Previous frame's sp is 0xffffd71c >> Saved registers: >> r31 at 0xffffd718, pc at 0xffffd720, lr at 0xffffd720 >> (gdb) cont >> Continuing. >> >> Program received signal SIGSEGV, Segmentation fault. >> 0x419a89c8 in memcpy (dst0=0xffffd6f4, src0=<optimized out>, >> length=<optimized out>) at /usr/src/lib/libc/string/bcopy.c:124 >> warning: Source file is more recent than executable. >> 124 TLOOP1(*--dst = *--src); > > So misaligned (multiple of 4 but of no higher power of 2) for "frame at", > "called by frame at" (which is listed as the same as "frame at"), "Arglist", > "Locals", and "Previous frame's sp" (which is listed as the same as "frame > at"). > > > > More context notes. . . > > The "pure gcc 4.2.1 buildworld/buildkernel system" has: > > # freebsd-version -ku; uname -aKU > 11.0-CURRENT > 11.0-CURRENT > FreeBSD FBSDG4C0 11.0-CURRENT FreeBSD 11.0-CURRENT #5 r294960M: Wed Jan 27 > 18:25:04 PST 2016 > root@FBSDG4C0:/usr/obj/gcc421/powerpc.powerpc/usr/src/sys/GENERICvtsc-NODEBUG > powerpc 1100097 1100097 > > > The "clang 3.8.0 buildworld and gcc 4.2.1 buildkernel mix" has: > > # freebsd-version -ku; uname -aKU > 11.0-CURRENT > 11.0-CURRENT > FreeBSD FBSDG4C1 11.0-CURRENT FreeBSD 11.0-CURRENT #1 r294962M: Fri Jan 29 > 18:28:17 PST 2016 > markmi@FreeBSDx64:/usr/obj/clang_gcc421/powerpc.powerpc/usr/src/sys/GENERICvtsc-NODEBUG > powerpc 1100097 1100097 > > (Same PowerMac, different SSD.) > > > [I have renamed a.out's to indicate compiler context as I've gone along.] > [I copied each a.out to the other SSD for use after compiling/linking.] > [I'm not generally showing the "direct call" properly aligned "info frame" > texts.] > [handle SIGINFO nostop print pass; break handler used in gdb 7.10_5.] > [For gcc 4.2.1 I used: gcc -std=c99 -Wall sig_snprintf_use_test.c .] > [For clang 3.8.0 I used: clang -std=c11 -Wall -Wpedantic > sig_snprintf_use_test.c .] > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Jan-31, at 6:32 PM, Mark Millard <markmi at dsl-only.net> wrote: > >> [I've never noticed gcc 4.2.1 generating code that was based on presuming >> the alignment was present. For example: it always seems to use addition to >> deal with address offsets, never masking. So I'd not expect to see >> segmentation faults for that context even when the stack is aligned modulo >> only 4. Separately checking the alignment is appropriate for me to do.] >> >> A) The reported context: >> >> The kernel context here is a gcc 4.2.1 based buildkernel then installkernel. >> The world context here is a clang 3.8.0 based buildworld then installworld. >> The program context here is a clang 3.8.0 based: >> >>> # clang -std=c11 -Wall -Wpedantic sig_snprintf_use_test.c >>> # /usr/local/bin/gdb a.out >> >> >> Using "break handler" in gdb (7.10_5) and using "info frame" when it stops >> for the "raise" shows the misalignment of the frame that the handler was >> given ny the signal delivery. >> >> By contrast the earlier direct call of the handler gets a "info frame" >> result that shows the expected sort of alignment. >> >> I find no evidence of frame/stack misalignment via gdb except for the one >> that is created by the signal delivery. >> >> >> B) I'll look at trying one or more of gcc 4.2.1, gcc49, gcc5 for the program >> context, still based on a clang 3.8.0 buildworld and gcc 4.2.1 buildkernel >> based on projects/clang380-import (-r294962). >> >> C) I will look at trying the same program builds on a pure gcc 4.2.1 >> buildworld/buildkernel context. (Likely 11.0-CURRENT -r294960.) >> >> >> I'll send more results when I have them. >> >> > > > > > === > Mark Millard > markmi at dsl-only.net > > On 2016-Jan-31, at 5:50 PM, Justin Hibbits <chmeeedalf at gmail.com> wrote: > > Does this occur with gcc-built world and/or kernel? You could put some > printf()s in sendsig(), and there are KTR tracepoints already present. The > code assumes a fully aligned user stack, which should be correct, but may not > be. > > - Justin > On Jan 31, 2016, at 6:41 PM, Mark Millard wrote: > >> I have submitted Bug 206810 for this 11.0-CURRENT/clang380-import stack >> alignment problem for TARGET_ARCH=powerpc signal delivery. >> >> === >> Mark Millard >> markmi at dsl-only.net >> >> On 2016-Jan-31, at 6:08 AM, Roman Divacky <rdivacky at vlakno.cz> wrote: >> >> Fwiw, LLVM expect 16B aligned stack on PowerPC. >> >> On Sun, Jan 31, 2016 at 05:55:20AM -0800, Mark Millard wrote: >>> 3 quick FreeBSD for powerpc (32-bit) questions: >>> >>> >>> A) For PowerPC (32-bit) what is the stack alignment requirement by the >>> ABI(s) that FreeBSD targets? >>> >>> B) Are signal handlers supposed to be given that alignment? >>> >>> >>> I ask because signal handlers are at times begin given just 4-byte >>> alignment but clang 3.8.0 powerpc's code generation can depend on the >>> alignment being more than 4. >>> >>> clang 3.8.0 can calculate addresses by, for example, masking in a 0x4 >>> relative to what would need to be an aligned address with alignment 8 or >>> more instead of adding 0x4 to a more arbitrary address. >>> >>> So far I've only seen less than 8 byte stack alignment via signal handler >>> activity. >>> >>> >>> C) Which should be blamed for problems here: clang's code generation, >>> FreeBSD's stack alignment handling for signals, or both? >>> >>> === >>> Mark Millard >>> markmi at dsl-only.net >>> >>> _______________________________________________ >>> freebsd-toolchain@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-toolchain >>> To unsubscribe, send any mail to "freebsd-toolchain-unsubscr...@freebsd.org" >> > > > > > > > _______________________________________________ freebsd-toolchain@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-toolchain To unsubscribe, send any mail to "freebsd-toolchain-unsubscr...@freebsd.org"