[Git][ghc/ghc][wip/T21964] ncg/aarch64: Don't use x18 register on AArch64/Darwin

[Ben Gamari (@bgamari)]

Ben Gamari pushed to branch wip/T21964 at Glasgow Haskell Compiler / GHC


Commits:
7c3b4193 by normalcoder at 2022-08-09T13:48:59-04:00
ncg/aarch64: Don't use x18 register on AArch64/Darwin

Apple's ABI documentation [1] says: "The platforms reserve register x18.
Don’t use this register." While this wasn't problematic in previous
Darwin releases, macOS 13 appears to start zeroing this register
periodically. See #21964.

[1] https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms

- - - - -


1 changed file:

- compiler/CodeGen.Platform.h


Changes:

=====================================
compiler/CodeGen.Platform.h
=====================================
@@ -926,6 +926,14 @@ freeReg 29 = False
 -- ip0 -- used for spill offset computations
 freeReg 16 = False
 
+#if defined(darwin_HOST_OS) || defined(ios_HOST_OS)
+-- x18 is reserved by the platform on Darwin/iOS, and can not be used
+-- More about ARM64 ABI that Apple platforms support:
+-- https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms
+-- https://github.com/Siguza/ios-resources/blob/master/bits/arm64.md
+freeReg 18 = False
+#endif
+
 # if defined(REG_Base)
 freeReg REG_Base  = False
 # endif



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7c3b4193b07bea8e2f7820d731c74e4057c1f9ff

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7c3b4193b07bea8e2f7820d731c74e4057c1f9ff
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