Re: [go-nuts] How does stack overflow handles in gollvm

2021-06-24 Thread 'Than McIntosh' via golang-nuts 
Hello,

If you go into your LLVM IR dump and look at the place where the function
is defined, you'll see a reference to an attribute set, e.g.

  define void @main.foo(i8* nest %nest.1) #0 !dbg !16 {

Here "#0" refers to this attribute set (appearing later in the dump):

attributes #0 = { "disable-tail-calls"="true" "frame-pointer"="none"
"null-pointer-is-valid"="true" "split-stack" "target-cpu"="x86-64"
"target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" }

One of these attributes is "split-stack". When this attribute is set, the
LLVM back end will emit a stack check in the prolog with a call to expand
the stack if needed.

You can find this code at

https://github.com/llvm/llvm-project/blob/25bb61649085c0a6e66630bbffe7faa54cd67829/llvm/lib/CodeGen/PrologEpilogInserter.cpp#L1128

Hope this helps.

Thanks, Than

On Wed, Jun 23, 2021 at 11:11 PM Kavindu Gimhan Zoysa 
wrote:

> Hi Kurtis,
>
> Thank you for your input.
>
> I am searching how do languages handle stack overflow. Languages like
> rust, handle this by catching SIGSEGV. In golang, as I found, it was
> handled by increasing the stack[1], [2] (Sorry if my terms are wrong). I
> have generated object dump(objdump -d) for go source code (just a function
> call) I can see that at the beginning of every function call it checks for
> the stack overflow and try to increase the stack(see //go:nosplit section
> of [2]). I am lloking how does gollvm handle this.
>
> *004871a0 :*
> *  4871a0: 64 48 8b 0c 25 f8 ff mov%fs:0xfff8,%rcx*
> *  4871a7: ff ff *
> *  4871a9: 48 8d 44 24 f8lea-0x8(%rsp),%rax*
> *  4871ae: 48 3b 41 10  cmp0x10(%rcx),%rax*
> *  4871b2: 0f 86 e1 00 00 00jbe487299 *
> **
> *  487299: e8 62 80 fc ffcallq  44f300
> *
> *  48729e: e9 fd fe ff ffjmpq   4871a0 *
>
> [1]:
> https://github.com/golang/go/blob/02ab8d1a1dc82ce019969221313bfa28911f54a1/src/runtime/stack.go#L28
> [2]: https://dave.cheney.net/2018/01/08/gos-hidden-pragmas
> On Thursday, 24 June 2021 at 08:17:33 UTC+5:30 Kurtis Rader wrote:
>
>> This might be an XY Problem , or your question
>> simply needs more context. Your sample program is an example of infinite
>> recursion. How that is detected is platform specific. It might be done via
>> a special signal. Or it might be done by a syscall to grow the stack
>> returning an error. So my question is, why are you asking how infinite
>> recursion is handled?
>>
>> On Wed, Jun 23, 2021 at 7:33 PM Kavindu Gimhan Zoysa 
>> wrote:
>>
>>> Hi all,
>>>
>>> *package main*
>>>
>>> *func main() {*
>>> * foo()*
>>> *}*
>>>
>>> *func foo() {*
>>> * a := 5*
>>> * _ = a*
>>> * foo()*
>>> *}*
>>>
>>> I have generated the below llvm ir using the command `./bin/llvm-goc -S
>>> test.go -dump-ir`. I expected there are some llvm intrinsics that have been
>>> used to handle stack overflow. But it is not there. How does gollvm handle
>>> stackoverflow?
>>>
>>> *define void @main.main(i8* nest %nest.0) #0 !dbg !14 {*
>>> *entry:*
>>> *  call void @main.foo(i8* nest undef), !dbg !15*
>>> *  ret void*
>>> *}*
>>>
>>> *define void @main.foo(i8* nest %nest.1) #0 !dbg !16 {*
>>> *entry:*
>>> *  %a = alloca i64, align 8*
>>> *  %0 = bitcast i64* %a to i8**
>>> *  call void @llvm.lifetime.start.p0i8(i64 8, i8* %0)*
>>> *  store i64 5, i64* %a, align 8*
>>> *  call void @llvm.dbg.declare(metadata i64* %a, metadata !17, metadata
>>> !DIExpression()), !dbg !20*
>>> *  %a.ld.0 = load i64, i64* %a, align 8, !dbg !21*
>>> *  call void @main.foo(i8* nest undef), !dbg !22*
>>> *  %1 = bitcast i64* %a to i8**
>>> *  call void @llvm.lifetime.end.p0i8(i64 8, i8* %1)*
>>> *  ret void*
>>> *}*
>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "golang-nuts" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to golang-nuts...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/golang-nuts/0bbb1347-5ceb-4ed2-9622-cb695d29bc6dn%40googlegroups.com
>>> 
>>> .
>>>
>>
>>
>> --
>> Kurtis Rader
>> Caretaker of the exceptional canines Junior and Hank
>>
> --
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> 
> .
>

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Re: [go-nuts] How does stack overflow handles in gollvm

2021-06-23 Thread Kavindu Gimhan Zoysa 
Hi Kurtis,

Thank you for your input. 

I am searching how do languages handle stack overflow. Languages like rust, 
handle this by catching SIGSEGV. In golang, as I found, it was handled by 
increasing the stack[1], [2] (Sorry if my terms are wrong). I have 
generated object dump(objdump -d) for go source code (just a function call) 
I can see that at the beginning of every function call it checks for the 
stack overflow and try to increase the stack(see //go:nosplit section of 
[2]). I am lloking how does gollvm handle this. 

*004871a0 :*
*  4871a0: 64 48 8b 0c 25 f8 ff mov%fs:0xfff8,%rcx*
*  4871a7: ff ff *
*  4871a9: 48 8d 44 24 f8lea-0x8(%rsp),%rax*
*  4871ae: 48 3b 41 10  cmp0x10(%rcx),%rax*
*  4871b2: 0f 86 e1 00 00 00jbe487299 *
**
*  487299: e8 62 80 fc ffcallq  44f300 
*
*  48729e: e9 fd fe ff ffjmpq   4871a0 *

[1]: 
https://github.com/golang/go/blob/02ab8d1a1dc82ce019969221313bfa28911f54a1/src/runtime/stack.go#L28
[2]: https://dave.cheney.net/2018/01/08/gos-hidden-pragmas
On Thursday, 24 June 2021 at 08:17:33 UTC+5:30 Kurtis Rader wrote:

> This might be an XY Problem , or your question 
> simply needs more context. Your sample program is an example of infinite 
> recursion. How that is detected is platform specific. It might be done via 
> a special signal. Or it might be done by a syscall to grow the stack 
> returning an error. So my question is, why are you asking how infinite 
> recursion is handled?
>
> On Wed, Jun 23, 2021 at 7:33 PM Kavindu Gimhan Zoysa  
> wrote:
>
>> Hi all,
>>
>> *package main*
>>
>> *func main() {*
>> * foo()*
>> *}*
>>
>> *func foo() {*
>> * a := 5*
>> * _ = a*
>> * foo()*
>> *}*
>>
>> I have generated the below llvm ir using the command `./bin/llvm-goc -S 
>> test.go -dump-ir`. I expected there are some llvm intrinsics that have been 
>> used to handle stack overflow. But it is not there. How does gollvm handle 
>> stackoverflow?
>>
>> *define void @main.main(i8* nest %nest.0) #0 !dbg !14 {*
>> *entry:*
>> *  call void @main.foo(i8* nest undef), !dbg !15*
>> *  ret void*
>> *}*
>>
>> *define void @main.foo(i8* nest %nest.1) #0 !dbg !16 {*
>> *entry:*
>> *  %a = alloca i64, align 8*
>> *  %0 = bitcast i64* %a to i8**
>> *  call void @llvm.lifetime.start.p0i8(i64 8, i8* %0)*
>> *  store i64 5, i64* %a, align 8*
>> *  call void @llvm.dbg.declare(metadata i64* %a, metadata !17, metadata 
>> !DIExpression()), !dbg !20*
>> *  %a.ld.0 = load i64, i64* %a, align 8, !dbg !21*
>> *  call void @main.foo(i8* nest undef), !dbg !22*
>> *  %1 = bitcast i64* %a to i8**
>> *  call void @llvm.lifetime.end.p0i8(i64 8, i8* %1)*
>> *  ret void*
>> *}*
>>
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to golang-nuts...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/golang-nuts/0bbb1347-5ceb-4ed2-9622-cb695d29bc6dn%40googlegroups.com
>>  
>> 
>> .
>>
>
>
> -- 
> Kurtis Rader
> Caretaker of the exceptional canines Junior and Hank
>

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Re: [go-nuts] How does stack overflow handles in gollvm

2021-06-23 Thread Kurtis Rader 
This might be an XY Problem , or your question
simply needs more context. Your sample program is an example of infinite
recursion. How that is detected is platform specific. It might be done via
a special signal. Or it might be done by a syscall to grow the stack
returning an error. So my question is, why are you asking how infinite
recursion is handled?

On Wed, Jun 23, 2021 at 7:33 PM Kavindu Gimhan Zoysa 
wrote:

> Hi all,
>
> *package main*
>
> *func main() {*
> * foo()*
> *}*
>
> *func foo() {*
> * a := 5*
> * _ = a*
> * foo()*
> *}*
>
> I have generated the below llvm ir using the command `./bin/llvm-goc -S
> test.go -dump-ir`. I expected there are some llvm intrinsics that have been
> used to handle stack overflow. But it is not there. How does gollvm handle
> stackoverflow?
>
> *define void @main.main(i8* nest %nest.0) #0 !dbg !14 {*
> *entry:*
> *  call void @main.foo(i8* nest undef), !dbg !15*
> *  ret void*
> *}*
>
> *define void @main.foo(i8* nest %nest.1) #0 !dbg !16 {*
> *entry:*
> *  %a = alloca i64, align 8*
> *  %0 = bitcast i64* %a to i8**
> *  call void @llvm.lifetime.start.p0i8(i64 8, i8* %0)*
> *  store i64 5, i64* %a, align 8*
> *  call void @llvm.dbg.declare(metadata i64* %a, metadata !17, metadata
> !DIExpression()), !dbg !20*
> *  %a.ld.0 = load i64, i64* %a, align 8, !dbg !21*
> *  call void @main.foo(i8* nest undef), !dbg !22*
> *  %1 = bitcast i64* %a to i8**
> *  call void @llvm.lifetime.end.p0i8(i64 8, i8* %1)*
> *  ret void*
> *}*
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/0bbb1347-5ceb-4ed2-9622-cb695d29bc6dn%40googlegroups.com
> 
> .
>


-- 
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank

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[go-nuts] How does stack overflow handles in gollvm

2021-06-23 Thread Kavindu Gimhan Zoysa 
Hi all,

*package main*

*func main() {*
* foo()*
*}*

*func foo() {*
* a := 5*
* _ = a*
* foo()*
*}*

I have generated the below llvm ir using the command `./bin/llvm-goc -S 
test.go -dump-ir`. I expected there are some llvm intrinsics that have been 
used to handle stack overflow. But it is not there. How does gollvm handle 
stackoverflow?

*define void @main.main(i8* nest %nest.0) #0 !dbg !14 {*
*entry:*
*  call void @main.foo(i8* nest undef), !dbg !15*
*  ret void*
*}*

*define void @main.foo(i8* nest %nest.1) #0 !dbg !16 {*
*entry:*
*  %a = alloca i64, align 8*
*  %0 = bitcast i64* %a to i8**
*  call void @llvm.lifetime.start.p0i8(i64 8, i8* %0)*
*  store i64 5, i64* %a, align 8*
*  call void @llvm.dbg.declare(metadata i64* %a, metadata !17, metadata 
!DIExpression()), !dbg !20*
*  %a.ld.0 = load i64, i64* %a, align 8, !dbg !21*
*  call void @main.foo(i8* nest undef), !dbg !22*
*  %1 = bitcast i64* %a to i8**
*  call void @llvm.lifetime.end.p0i8(i64 8, i8* %1)*
*  ret void*
*}*

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