6 ms·

Awesome! Any chance you, or anyone else has documentation on x86_64 Windows calling conventions? That's where I've been getting stuck.

afranchuk 8y ago
IIRC: while it's not explicitly documented, x86_64 was late enough in the game that both windows and Unix systems have the same calling convention. Saves a lot of hassle :)
- jcranmer 8y ago
  Nope, the Windows ABI uses a different set of registers than the SysV (Unix) ABI. SysV uses rdi, rsi, rdx, rcx, r8, r9 (in that order), and Windows uses rcx, rdx, r8, r9 (in that order).
  - billti 8y ago
    It's not just the registers, the use of the stack (e.g. lack of a "red zone" on Windows) as well as the data used for exception handling are different too. The MSDN links above are quite detailed on what Windows implements. The post by Eli at https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64/ https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-... goes over some Windows differences towards the end.
- int_19h 8y ago
  They do not use the same convention. AMD did define a calling convention as part of their SysV ABI spec, and pretty much everybody adopted that ABI... except for Windows. As to why, the best we have is informed speculation: https://stackoverflow.com/questions/4429398/why-does-windows64-use-a-different-calling-convention-from-all-other-oses-on-x86 https://stackoverflow.com/questions/4429398/why-does-windows...
CalChris 8y ago
https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019 https://docs.microsoft.com/en-us/cpp/build/x64-calling-conve... After you read that, you might want to look at the LLVM source https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X86/X86CallingConv.td https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X... /// The C convention as implemented on Windows/x86-64 and /// AArch64. This convention differs from the more common /// \c X86_64_SysV convention in a number of ways, most notably in /// that XMM registers used to pass arguments are shadowed by GPRs, /// and vice versa. /// On AArch64, this is identical to the normal C (AAPCS) calling /// convention for normal functions, but floats are passed in integer /// registers to variadic functions.

afranchuk 8y ago

IIRC: while it's not explicitly documented, x86_64 was late enough in the game that both windows and Unix systems have the same calling convention. Saves a lot of hassle :)

jcranmer 8y ago
Nope, the Windows ABI uses a different set of registers than the SysV (Unix) ABI. SysV uses rdi, rsi, rdx, rcx, r8, r9 (in that order), and Windows uses rcx, rdx, r8, r9 (in that order).
- billti 8y ago
  It's not just the registers, the use of the stack (e.g. lack of a "red zone" on Windows) as well as the data used for exception handling are different too. The MSDN links above are quite detailed on what Windows implements. The post by Eli at https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64/ https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-... goes over some Windows differences towards the end.
int_19h 8y ago
They do not use the same convention. AMD did define a calling convention as part of their SysV ABI spec, and pretty much everybody adopted that ABI... except for Windows. As to why, the best we have is informed speculation: https://stackoverflow.com/questions/4429398/why-does-windows64-use-a-different-calling-convention-from-all-other-oses-on-x86 https://stackoverflow.com/questions/4429398/why-does-windows...

CalChris 8y ago

https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019 https://docs.microsoft.com/en-us/cpp/build/x64-calling-conve... After you read that, you might want to look at the LLVM source https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X86/X86CallingConv.td https://github.com/llvm-mirror/llvm/blob/master/lib/Target/X... /// The C convention as implemented on Windows/x86-64 and /// AArch64. This convention differs from the more common /// \c X86_64_SysV convention in a number of ways, most notably in /// that XMM registers used to pass arguments are shadowed by GPRs, /// and vice versa. /// On AArch64, this is identical to the normal C (AAPCS) calling /// convention for normal functions, but floats are passed in integer /// registers to variadic functions.