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Add comment in Memory.inc explaining r175646.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175650 91177308-0d34-0410-b5e6-96231b3b80d8
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Krzysztof Parzyszek 2013-02-20 19:25:09 +00:00
parent 09adcf7dca
commit 033ee0f111
1 changed files with 7 additions and 0 deletions
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7
lib/Support/Unix/Memory.inc
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@ -52,6 +52,13 @@ int getPosixProtectionFlags(unsigned Flags) {
return PROT_READ | PROT_WRITE | PROT_EXEC;
case llvm::sys::Memory::MF_EXEC:
#if defined(__FreeBSD__)
// On PowerPC, having an executable page that has no read permission
// can have unintended consequences. The function InvalidateInstruction-
// Cache uses instructions dcbf and icbi, both of which are treated by
// the processor as loads. If the page has no read permissions,
// executing these instructions will result in a segmentation fault.
// Somehow, this problem is not present on Linux, but it does happen
// on FreeBSD.
return PROT_READ | PROT_EXEC;
#else
return PROT_EXEC;