#4992: LLVM trashes registers for primitive calls
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Reporter: scpmw | Owner: davidterei@…
Type: bug | Status: patch
Priority: normal | Milestone:
Component: Compiler (LLVM) | Version: 7.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: Runtime crash
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Comment(by scpmw):
I have attached my best shot at reproducing the problem with just "tan".
It generates roughly the following code before the patch:
{{{
subq $72, %rsp
movq %r15, 40(%rsp) # 8-byte Spill
movq %r14, 32(%rsp) # 8-byte Spill
movq %r12, 24(%rsp) # 8-byte Spill
movq %rbp, 8(%rsp) # 8-byte Spill
movq %r13, 16(%rsp) # 8-byte Spill
movaps %xmm5, %xmm0
callq tan
cvttsd2siq %xmm0, %rax
movq %rax, 56(%rsp) # 8-byte Spill
}}}
And then goes on using all available registers, which is clearly
dangerous. With the patch applied, a lot more registers are saved on top
of the stack.
I'm unsure though how to craft an actually failing program out of this.
Maybe somebody with a better overview can put in the missing piece?
(Fun fact: The program actually manages to crash the LLVM optimizer both
with and without the patch. Compiling without -O works.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4992#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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