Date: Tue, 16 Feb 2016 05:51:51 -0800 From: Mark Millard <markmi@dsl-only.net> To: Roman Divacky <rdivacky@vlakno.cz> Cc: Nathan Whitehorn <nwhitehorn@freebsd.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: I've submitted 207175 for a clang 3.8.0 va_list handling problem for powerpc Message-ID: <28FF474D-2109-4605-8B2B-C5374CBCCF42@dsl-only.net> In-Reply-To: <74577A87-3006-43A9-9EAB-F51D946B6245@dsl-only.net> References: <F6846682-10F7-4D0D-A691-ED8D4366805C@dsl-only.net> <20160214192903.GA96697@vlakno.cz> <70B405C4-E1AC-4F35-9786-051FDA2F8BE7@dsl-only.net> <D7D536A4-68B6-4506-BDFB-8C2C41E1C958@dsl-only.net> <20160215191100.GA17387@vlakno.cz> <3A260EC5-E69A-4980-8F74-C04395F4E5F4@dsl-only.net> <20160215201800.GA20796@vlakno.cz> <D702187C-6B8C-42AC-855D-45A570FDB0FA@dsl-only.net> <D3351840-02B5-4696-8163-D90A6E039E4C@dsl-only.net> <74577A87-3006-43A9-9EAB-F51D946B6245@dsl-only.net>
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By the way: Nothing tested or seen so far checks DOUBLE_OR_FLOAT = handling. That involves fr (fpr in va_list in clang terms) instead of gr/gpr. = fr/fpr has its own independent count and bound for using floating point = registers vs. using the overflow area. There is also condition register = bit 6 that indicates if floating point is involved overall or not. Ultimately which of gpr vs. fpr and which bound (if the numbers are = distinct in value) depends on the type specified in va_arg = (SIMPLE_ARG/LONG_LONG vs. DOUBLE_OR_FLOAT status). This may mean that the fix is an improvement for some types of usage but = not a complete update: It is wrong for DOUBLE_OR_FLOAT instances of = var_arg as stands. fpr would need to be involved instead. For world I = expect it is fairly generally an improvement. Also if the condition register indicates floating point is involved = overall then there is likely management/handling of floating point state = (for context switching management). (If it indicates no floating point = involvement then there might be optimizations possible.) =3D=3D=3D Mark Millard markmi at dsl-only.net On 2016-Feb-16, at 2:45 AM, Mark Millard <markmi@dsl-only.net> wrote: I used: > Index: /usr/src/contrib/llvm/tools/clang/lib/CodeGen/TargetInfo.cpp > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- /usr/src/contrib/llvm/tools/clang/lib/CodeGen/TargetInfo.cpp = (revision 295601) > +++ /usr/src/contrib/llvm/tools/clang/lib/CodeGen/TargetInfo.cpp = (working copy) > @@ -3569,6 +3569,8 @@ > { > CGF.EmitBlock(UsingOverflow); >=20 > + Builder.CreateStore(Builder.getInt8(8), NumRegsAddr); > + > // Everything in the overflow area is rounded up to a size of at = least 4. > CharUnits OverflowAreaAlign =3D CharUnits::fromQuantity(4); as my test change. (Get evidence of operation before potential cleanup = of the duplicated 8's.) After a full buildworld/installworld based on the updated compiler. . . My simple example of the problem no longer fails. "ls -l -n /" now works. "svnlite update -r295601 /usr/src" now works. So whatever you want to do for the details of any submitted code, the = basics of the change do avoid the SEGVs and allow these programs to = work. =3D=3D=3D Mark Millard markmi at dsl-only.net On 2016-Feb-15, at 4:27 PM, Mark Millard <markmi@dsl-only.net> wrote: On 2016-Feb-15, at 1:20 PM, Mark Millard <markmi at dsl-only.net> wrote: >=20 > On 2016-Feb-15, at 12:18 PM, Roman Divacky <rdivacky at vlakno.cz> = wrote: >>=20 >> On Mon, Feb 15, 2016 at 12:17:50PM -0800, Mark Millard wrote: >>> On 2016-Feb-15, at 11:11 AM, Roman Divacky <rdivacky at vlakno.cz> = wrote: >>>>=20 >>>> Mark, I believe you're right. What do you think about this patch? >>>>=20 >>>> Index: tools/clang/lib/CodeGen/TargetInfo.cpp >>>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D >>>> --- tools/clang/lib/CodeGen/TargetInfo.cpp (revision 260852) >>>> +++ tools/clang/lib/CodeGen/TargetInfo.cpp (working copy) >>>> @@ -3599,6 +3599,8 @@ >>>> { >>>> CGF.EmitBlock(UsingOverflow); >>>>=20 >>>> + Builder.CreateStore(Builder.getInt8(11), NumRegsAddr); >>>> + >>>> // Everything in the overflow area is rounded up to a size of at = least 4. >>>> CharUnits OverflowAreaAlign =3D CharUnits::fromQuantity(4); >>>>=20 >>>>=20 >>>> Can you test it? >>>=20 >>> It may be later today before I can start the the test process. >>>=20 >>> While your change is not wrong as presented, it does seem to be = based on the ABI document's numbering with the range 3 <=3D gr <12, = where 3 <=3D gr < 11 cover r3-r10 use and gr=3D11 implies overflow stack = area use. (gr being the ABI documents name.) >>>=20 >>> The clang code generation that I saw while analyzing the problem and = the clang source that you had me look at did not use that numbering. = Instead it seems to be based on 0 <=3D gpr < 9, where 0 <=3D gpr < 8 = cover r3-r10 use and gpr=3D8 implies overflow stack area use. (gpr being = what gdb showed me as I remember.) In other words: clang counts the = number of "parameter registers" already in use as it goes along instead = of tracking register numbers that have been used. >>>=20 >>> So assigning any value that appears to be positive and >=3D 8 should = work, such as: >>>=20 >>> Builder.CreateStore(Builder.getInt8(8), NumRegsAddr); >>=20 >> Can you check what number gcc uses? We want to be interoperable with = gcc. >>=20 >> Anyway, thanks for testing! >>=20 >> Roman >=20 > I'll do that check of gcc 4.2.1 code generation before starting the = test later today. >=20 > But if the clang numbering is different in gcc 4.2.1 then far more = than just adding a >=20 >> Builder.CreateStore(Builder.getInt8(?), NumRegsAddr) >=20 >=20 > for some "?" would need to be involved in the changes in order to = reach compatibility. >=20 >=20 > I'll note that for clang 3.8.0 the actual comparison instruction = generated is of the form >=20 >> cmplwi r?,7 >=20 >=20 > for some r?, such as r5 or r4, and the conditional branch generated is = a bgt instruction. >=20 > =3D=3D=3D > Mark Millard > markmi at dsl-only.net gcc 4.2.1 generates comparison instructions for va_arg of the form: cmplwi cr7,r0,8 and the conditional branch generated is a "bge cr7, . . ." instruction. So the same number range is in use by both compilers: They are = compatible for the bounds checks for reg vs. overflow for how they = count, equality inclusion/exclusion matching up with the specific number = (8 vs. 7) used to make things the same overall. Other aspects of the code generation distinctions would take me time to = analyze. It will be a while before I will be looking at other points. =3D=3D=3D Mark Millard markmi at dsl-only.net
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