I've submitted 207175 for a clang 3.8.0 va_list handling problem for powerpc [fpr use also tested]
Mark Millard
markmi at dsl-only.net
Sat Feb 20 09:03:00 UTC 2016
Thanks!
llvm bugzilla's 26605 did not having anything yet for this so I've copied over your note. But I've left the status alone.
The next thing that I ran into looks nastier: c++'s exception handling is broken.
#include <exception>
int main(void)
{
try { throw std::exception(); }
catch (std::exception& e) {} // same result without &
return 0;
}
does not work on powerpc (SEGV) or powerpc64 (unbounded loop, never returning from _Unwind_RaiseException). (The powerpc64 context is using devel/powerpc64-gcc or g++49 as the compiler with the system's headers and libraries. powerpc64-gcc was used for buildworld/buildkernel as well for this context.)
[g++49 using its own headers and libraries works fine for the above program.]
===
Mark Millard
markmi at dsl-only.net
On 2016-Feb-20, at 12:34 AM, Roman Divacky <rdivacky at vlakno.cz> wrote:
Fwiw, I've just committed the patch to clang in r261422. You might want
to keep using a local modification or ask dim@ to import that patch
to our copy of 3.8.
Thanks for your diagnosis and testing!
Roman
On Thu, Feb 18, 2016 at 02:29:29PM -0800, Mark Millard wrote:
> On 2016-Feb-17, at 9:23 PM, Mark Millard <markmi at dsl-only.net> wrote:
>>
>> My fpr related notes/worries about the fix were wrong.
>>
>> I finally got some time to look at this again and I see that I somehow missed the following code when I looked before:
>>
>> // The calling convention either uses 1-2 GPRs or 1 FPR.
>> Address NumRegsAddr = Address::invalid();
>> if (isInt || IsSoftFloatABI) {
>> NumRegsAddr = Builder.CreateStructGEP(VAList, 0, CharUnits::Zero(), "gpr");
>> } else {
>> NumRegsAddr = Builder.CreateStructGEP(VAList, 1, CharUnits::One(), "fpr");
>> }
>>
>> So the
>>
>> Builder.CreateStore(Builder.getInt8(8), NumRegsAddr);
>>
>> in Case 2 is tracking gpr vs. fpr usage contexts as it should. Also:
>>
>> llvm::Value *NumRegs = Builder.CreateLoad(NumRegsAddr, "numUsedRegs");
>>
>> // "Align" the register count when TY is i64.
>> if (isI64 || (isF64 && IsSoftFloatABI)) {
>> NumRegs = Builder.CreateAdd(NumRegs, Builder.getInt8(1));
>> NumRegs = Builder.CreateAnd(NumRegs, Builder.getInt8((uint8_t) ~1U));
>> }
>>
>> llvm::Value *CC =
>> Builder.CreateICmpULT(NumRegs, Builder.getInt8(8), "cond");
>>
>> is using the same bounds check figure (8) for gpr and fpr.
>>
>> Apparently that common bound is one reason that the clang numbering is not the same as the ABI document's numbering: clang's numbering allows using the same figure for both contexts. (Given the prior alignment for isI64 (or isF64 with IsSoftFloatABI).)
>>
>> Sorry for the prior noise about fpr.
>>
>> It is still true that DOUBLE_OR_FLOAT is untested so far.
>>
>> ===
>> Mark Millard
>> markmi at dsl-only.net
>
> I finally got some time to apply to some basic testing involving double as well (for involving fpr use). . .
>
> No problems with exceptions. Looking at the memory contents at various stages in gdb looks good. va_list's gpr, fpr, overflow_arg_area changes as its va_args use progresses look good. Values extracted by va_args use looks good. Both default and -O2.
>
> The added
>
>> Builder.CreateStore(Builder.getInt8(8), NumRegsAddr);
>
>
> passes my checks. I've not observed any problems from buildworld materials, unlike when that line is missing.
>
> [Note: I run with the signal delivery modified to have a "red zone" to deal with other aspects of clang 3.8.0 code generation that are not ABI compliant for when the stack pointer is moved. Having a "red zone" is still operationally correct for an ABI compliant code generation, it just temporarily wastes more bytes. Also: the kernel was built with gcc 4.2.1 but world was built with clang 3.8.0.]
>
>
> ===
> Mark Millard
> markmi at dsl-only.net
>
> . . . [bad fpr related material omitted] . . .
>
> On 2016-Feb-16, at 2:45 AM, Mark Millard <markmi at dsl-only.net> wrote:
>
> I used:
>
>> Index: /usr/src/contrib/llvm/tools/clang/lib/CodeGen/TargetInfo.cpp
>> ===================================================================
>> --- /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);
>>
>> + Builder.CreateStore(Builder.getInt8(8), NumRegsAddr);
>> +
>> // Everything in the overflow area is rounded up to a size of at least 4.
>> CharUnits OverflowAreaAlign = 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.
>
>
> ===
> Mark Millard
> markmi at dsl-only.net
>
> On 2016-Feb-15, at 4:27 PM, Mark Millard <markmi at dsl-only.net> wrote:
>
> On 2016-Feb-15, at 1:20 PM, Mark Millard <markmi at dsl-only.net> wrote:
>>
>> On 2016-Feb-15, at 12:18 PM, Roman Divacky <rdivacky at vlakno.cz> wrote:
>>>
>>> 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:
>>>>>
>>>>> Mark, I believe you're right. What do you think about this patch?
>>>>>
>>>>> Index: tools/clang/lib/CodeGen/TargetInfo.cpp
>>>>> ===================================================================
>>>>> --- tools/clang/lib/CodeGen/TargetInfo.cpp (revision 260852)
>>>>> +++ tools/clang/lib/CodeGen/TargetInfo.cpp (working copy)
>>>>> @@ -3599,6 +3599,8 @@
>>>>> {
>>>>> CGF.EmitBlock(UsingOverflow);
>>>>>
>>>>> + Builder.CreateStore(Builder.getInt8(11), NumRegsAddr);
>>>>> +
>>>>> // Everything in the overflow area is rounded up to a size of at least 4.
>>>>> CharUnits OverflowAreaAlign = CharUnits::fromQuantity(4);
>>>>>
>>>>>
>>>>> Can you test it?
>>>>
>>>> It may be later today before I can start the the test process.
>>>>
>>>> While your change is not wrong as presented, it does seem to be based on the ABI document's numbering with the range 3 <= gr <12, where 3 <= gr < 11 cover r3-r10 use and gr=11 implies overflow stack area use. (gr being the ABI documents name.)
>>>>
>>>> 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 <= gpr < 9, where 0 <= gpr < 8 cover r3-r10 use and gpr=8 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.
>>>>
>>>> So assigning any value that appears to be positive and >= 8 should work, such as:
>>>>
>>>> Builder.CreateStore(Builder.getInt8(8), NumRegsAddr);
>>>
>>> Can you check what number gcc uses? We want to be interoperable with gcc.
>>>
>>> Anyway, thanks for testing!
>>>
>>> Roman
>>
>> I'll do that check of gcc 4.2.1 code generation before starting the test later today.
>>
>> But if the clang numbering is different in gcc 4.2.1 then far more than just adding a
>>
>>> Builder.CreateStore(Builder.getInt8(?), NumRegsAddr)
>>
>>
>> for some "?" would need to be involved in the changes in order to reach compatibility.
>>
>>
>> I'll note that for clang 3.8.0 the actual comparison instruction generated is of the form
>>
>>> cmplwi r?,7
>>
>>
>> for some r?, such as r5 or r4, and the conditional branch generated is a bgt instruction.
>>
>> ===
>> 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.
>
>
> ===
> Mark Millard
> markmi at dsl-only.net
>
>
>
>
>
>
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