Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.6.2  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-
Changes (by simonmar):

  * status:  infoneeded => new


Comment:

 I'm slightly unhappy about the solution to this ticket.  Since
 a9ce36118f0de3aeb427792f8f2c5ae097c94d3f we now align the stack to 16+8
 bytes on x86_64, which means that virtually every foreign call now looks
 like

 {{{
 subq $8,%rsp
 movl $0,%eax
 call foo
 addq $8,%rsp
 }}}

 since most calls on x86_64 pass arguments in registers, the 8 byte
 adjustment is to keep the alignment constraint after the return address is
 pushed.  (The assignment to `%eax` is to keep the ABI happy just in case
 the function we're calling is varargs, which is a separate issue).

 Now I understand the reason this was done, but I hate having to emit those
 two extra instructions around every call. I just wanted to record my
 dissatisfaction in this ticket in case it inspires someone to find a
 better solution :-)

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei
  Type:  task | Status:  infoneeded
  Priority:  normal   |  Milestone:  7.4.3 
 Component:  Compiler (LLVM)  |Version:  6.13  
Resolution:   |   Keywords:
Os:  MacOS X  |   Architecture:  x86   
   Failure:  None/Unknown | Difficulty:  Unknown   
  Testcase:   |  Blockedby:
  Blocking:   |Related:
--+-
Changes (by dterei):

 * cc: dmp@…, rice.edu (removed)
 * cc: dmp@… (added)


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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei
  Type:  task | Status:  infoneeded
  Priority:  normal   |  Milestone:  7.4.3 
 Component:  Compiler (LLVM)  |Version:  6.13  
Resolution:   |   Keywords:
Os:  MacOS X  |   Architecture:  x86   
   Failure:  None/Unknown | Difficulty:  Unknown   
  Testcase:   |  Blockedby:
  Blocking:   |Related:
--+-
Changes (by dterei):

  * status:  new => infoneeded


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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.4.3  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-
Changes (by dterei):

 * cc: dmp@… (removed)
 * cc: dmp@…, rice.edu (added)


Comment:

 Simon I can't reproduce. Just tested on Linux both 32bit and 64 bit
 machine and 5250 passes for llvm with current HEAD.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.4.2  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-
Changes (by simonmar):

  * milestone:  7.4.1 => 7.4.2


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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner:  dterei 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.4.1  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-
Changes (by dterei):

  * owner:  => dterei


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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner: 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.4.1  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-

Comment(by dterei):

 Argh! OK thanks Simon, will take a look when I get the time.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
--+-
  Reporter:  dterei   |  Owner: 
  Type:  task | Status:  new
  Priority:  normal   |  Milestone:  7.4.1  
 Component:  Compiler (LLVM)  |Version:  6.13   
Resolution:   |   Keywords: 
Os:  MacOS X  |   Architecture:  x86
   Failure:  None/Unknown | Difficulty:  Unknown
  Testcase:   |  Blockedby: 
  Blocking:   |Related: 
--+-
Changes (by simonmar):

  * owner:  dterei =>
  * difficulty:  => Unknown
  * status:  closed => new
  * resolution:  fixed =>


Comment:

 Re-opening this ticket as the test rts/5250(llvm) is failing on x86/linux,
 indicating that the stack pointer is not aligned correctly on that
 platform.  (David: I thought I had mentioned this before, but I searched
 around and can't find another ticket).

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.4.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dterei):

 Thanks for the patch, applied!

 Leaving ticket open though to trac fixing this on 32bit.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.4.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dmp@…):

 commit a9ce36118f0de3aeb427792f8f2c5ae097c94d3f
 {{{
 Author: David M Peixotto 
 Date:   Wed Oct 19 15:49:06 2011 -0500

 Change stack alignment to 16+8 bytes in STG code

 This patch changes the STG code so that %rsp to be aligned
 to a 16-byte boundary + 8. This is the alignment required by
 the x86_64 ABI on entry to a function. Previously we kept
 %rsp aligned to a 16-byte boundary, but this was causing
 problems for the LLVM backend (see #4211).

 We now don't need to invoke llvm stack mangler on
 x86_64 targets. Since the stack is now 16+8 byte algined in
 STG land on x86_64, we don't need to mangle the stack
 manipulations with the llvm mangler.

 This patch only modifies the alignement for x86_64 backends.

 Signed-off-by: David Terei 

  compiler/llvmGen/LlvmMangler.hs   |6 +++-
  compiler/nativeGen/X86/CodeGen.hs |   16 +++-
  rts/StgCRun.c |   46
 +
  3 files changed, 39 insertions(+), 29 deletions(-)
 }}}

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.4.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dmp):

 Yes the stack mangling has been disabled for the 64bit case so it's now
 only used for the 32bit darwin target. I might get some time to make the
 changes for the 32bit case too. Perhaps my reservations about the
 difficulties handling stdcall are unfounded.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.4.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dterei):

 Great! I'll have a look at the patch and hopefully merge. If you can
 handle the 32bit case that would be greatly appreciated though. I assume
 you disabled the llvm mangler stack fixup in the 64bit case but not 32bit?

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.4.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---
Changes (by dmp):

 * cc: dmp@… (added)


Comment:

 I have made the changes to keep the stack 16+8 byte aligned throughout
 STG code for x86_64 targets. The changes are available in my github
 repo on the 4211 branch

  https://github.com/dmpots/ghc/tree/4211

 I can also attach the patches to this ticket if that would work better.

 The results look promising. I get no new regressions on a validate run
 and a testsuite run with `WAY=optllvm` goes from 36 failures to 6
 failures, plus two unexpected passes (one of which is the 5250 test
 simonmar mentioned above).

 I would love to see these changes merged to the mainline GHC. I
 suppose that the main sticking point is probably that I made the
 change for 64-bit targets, but not the 32-bit targets. Is there any
 chance it will get merged for the 64-bit targets? My motivation (and
 therefore availble time) is much less for 32-bit targets and I'm
 worried that dealing with the `stdcall` convetion could be a bit more
 compilicated.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.2.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by simonmar):

 I just added a test for stack alignment for #5250, and sure enough it
 fails with LLVM:

 {{{
 => 5250(optllvm) 23 of 23 [0, 0, 0]
 cd . && '/64playpen/simonmar/validate/inplace/bin/ghc-stage2' -fforce-
 recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-conf
 -rtsopts  -o 5250 5250.hs -O -fllvm spalign.c  >5250.comp.stderr 2>&1
 cd . && ./52505250.run.stdout 2>5250.run.stderr
 Wrong exit code (expected 0 , actual 1 )
 Stdout:
 esp not aligned correctly: c39c5d30
 }}}

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.2.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dterei):

 OK. Yep I'll have a go at this sometime soon when I get some spare time.
 Probably won't have any for at least the next 10 days.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.2.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by simonmar):

 Right, C calls with no arguments will now need an esp adjustment, but I
 don't think it's a big deal (and it's only for calls with no arguments,
 those with arguments already need an Sp adjustment).

 Do you want to have a go?  There are only two places that need to be
 changed: `StgCRun.c`, where we currently add 12 to esp to align it, we can
 just drop that.  The other place is `X86.CodeGen.genCCall` where we pad
 the stack offset if necessary.

 Urgh, I just realised that we probably need to do something in
 `rts/Adjustor.c` too.  I looked at the code there, and the Darwin/x86
 version is vastly more complicated than the non-Darwin x86 version, and
 I'm surprised if all that complexity is needed just to get the stack
 pointer aligned...

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.2.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by dterei):

 Yes that would be great Simon, there shouldn't be any issues now that we
 don't support the registerised C backend. Only concern I can think of with
 this change is there may now be cases where the NCG didn't need to do any
 sp manipulation but now will. (E.g for any C calls the NCG will need to
 fix up alignment by subtracting 12 (or 8 on x64), while in the past if no
 system stack was used the sp was already correctly aligned). I can't see
 this causing any performance regression though.

 If you are happy to just take over this ticket thats great, otherwise just
 point me to what needs to be changed and I'll finish it off. I think when
 I had a very brief go at this ticket ages back the main problem was just
 finding all the locations involved in Sp tracking and manipulation.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.2.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---

Comment(by simonmar):

 I'm changing the code that handles stack alignment as a result of #5250, I
 think this change would be easy to make too.  David, ping me if you want
 help with this.

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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  7.0.1   
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---
Changes (by PHO):

 * cc: p...@… (added)


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Re: [GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |Owner:  dterei  
Type:  task |   Status:  new 
Priority:  normal   |Milestone:  6.14.1  
   Component:  Compiler (LLVM)  |  Version:  6.13
Keywords:   | Testcase:  
   Blockedby:   |   Difficulty:  
  Os:  MacOS X  | Blocking:  
Architecture:  x86  |  Failure:  None/Unknown
+---
Changes (by igloo):

  * milestone:  => 6.14.1


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[GHC] #4211: LLVM: Stack alignment on OSX

[GHC]

#4211: LLVM: Stack alignment on OSX
+---
Reporter:  dterei   |   Owner:  dterei 
Type:  task |  Status:  new
Priority:  normal   |   Component:  Compiler (LLVM)
 Version:  6.13 |Keywords: 
  Os:  MacOS X  |Testcase: 
Architecture:  x86  | Failure:  None/Unknown   
+---
 On OSX the ABI requires that the stack is 16 byte aligned when making
 function calls. (Although this only really needs to be obeyed when making
 calls that will go through the dynamic linker, so FFI calls). Since the
 stack is 16 byte aligned at the site of the call, on entry to a function
 most compilers (both llvm and gcc) expect the stack to now be aligned to
 16n - 4, since 4 bytes should have been pushed for the return address as
 part of the call instruction. GHC though since it uses jumps everywhere
 keeps that stack at 16 byte aligned on function entrance. This means that
 LLVM generates incorrect stack alignment code, always off by 4.

 For the moment I have handled this by using the LLvm Mangler (which is
 only needed on OS X already for TNTC) to simply correctly fix up the stack
 alignment code.

 E.g Asm generated by LLVM:
 {{{
 _func:
 subl $12, %esp
 ...
 call _sin
 ...
 addl $12, %esp
 }}}

 The mangler will change this to:
 {{{
 _func:
 subl $16, %esp
 ...
 call _sin
 ...
 addl $16, %esp
 }}}

 The better solution would be to change GHC to keep the stack at 16n - 4
 alignment on function. This will require changing the RTS (StgCRun.hs) to
 set the stack properly before calling into Stg land and also fixing up the
 NCG to align code properly. There may also be a problem with the C backend
 as currently all function prolouge and epilouge code is stripped out,
 which means all the stack manipulation code generated by GCC is removed.
 This works fine now since the stack is already 16 byte aligned on entry,
 but if it is now 16n - 4 byte aligned then some stack manipulation will be
 required.

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