Re: [PATCH 02/10] mach: Define MACHINE_THREAD_STATE_SETUP_CALL

[Samuel Thibault]

Applied, thanks!

Sergey Bugaev via Libc-alpha, le mer. 17 mai 2023 22:14:28 +0300, a ecrit:
> The existing two macros, MACHINE_THREAD_STATE_SET_PC and
> MACHINE_THREAD_STATE_SET_SP, can be used to set program counter and the
> stack pointer registers in a machine-specific thread state structure.
> 
> Useful as it is, this may not be enough to set up the thread to make a
> function call, because the machine-specific ABI may impose additional
> requirements. In particular, x86_64 ABI requires that upon function
> entry, the stack pointer is 8 less than 16-byte aligned (sp & 15 == 8).
> 
> To deal with this, introduce a new macro,
> MACHINE_THREAD_STATE_SETUP_CALL (), which sets both stack and
> instruction pointers, and also applies any machine-specific requirements
> to make a valid function call. The default implementation simply
> forwards to MACHINE_THREAD_STATE_SET_PC and MACHINE_THREAD_STATE_SET_SP,
> but on x86_64 we additionally align the stack pointer.
> 
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
> Any ideas for a better name than PTR_ALIGN_DOWN_8_16?
> 
>  sysdeps/mach/thread_state.h     |  9 +++++++++
>  sysdeps/mach/x86/thread_state.h | 13 +++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/sysdeps/mach/thread_state.h b/sysdeps/mach/thread_state.h
> index 9fa3d4e1..431aaf82 100644
> --- a/sysdeps/mach/thread_state.h
> +++ b/sysdeps/mach/thread_state.h
> @@ -38,6 +38,15 @@
>  #endif
>  #endif
>  
> +/* Set up the thread state to call the given function on the given state.
> +   Dependning on architecture, this may imply more than just setting PC
> +   and SP.  */
> +#ifndef MACHINE_THREAD_STATE_SETUP_CALL
> +#define MACHINE_THREAD_STATE_SETUP_CALL(ts, stack, size, func) \
> +  (MACHINE_THREAD_STATE_SET_PC (ts, func), \
> +   MACHINE_THREAD_STATE_SET_SP (ts, stack, size))
> +#endif
> +
>  /* This copies architecture-specific bits from the current thread to the new
>     thread state.  */
>  #ifndef MACHINE_THREAD_STATE_FIX_NEW
> diff --git a/sysdeps/mach/x86/thread_state.h b/sysdeps/mach/x86/thread_state.h
> index 5be0bec1..8c419515 100644
> --- a/sysdeps/mach/x86/thread_state.h
> +++ b/sysdeps/mach/x86/thread_state.h
> @@ -20,6 +20,7 @@
>  #define _MACH_X86_THREAD_STATE_H 1
>  
>  #include <mach/machine/thread_status.h>
> +#include <libc-pointer-arith.h>
>  
>  /* This lets the kernel define segments for a new thread.  */
>  #define MACHINE_NEW_THREAD_STATE_FLAVOR      i386_THREAD_STATE
> @@ -54,6 +55,18 @@ struct machine_thread_all_state
>      struct i386_float_state fpu;
>    };
>  
> +#ifdef __x86_64__
> +/* We're setting up the stack to perform a function call.  On function entry,
> +   the stack pointer must be 8 bytes less than 16-aligned.  */
> +#define PTR_ALIGN_DOWN_8_16(ptr)                                           \
> + ({ uintptr_t __ptr = PTR_ALIGN_DOWN (ptr, 8);                               
>       \
> +    PTR_IS_ALIGNED (__ptr, 16) ? (__ptr - 8) : __ptr; })
> +
> +#define MACHINE_THREAD_STATE_SETUP_CALL(ts, stack, size, func)               
>       \
> +  ((ts)->SP = PTR_ALIGN_DOWN_8_16 ((uintptr_t) (stack) + (size)),          \
> +   (ts)->PC = (uintptr_t) func)
> +#endif
> +
>  #include <sysdeps/mach/thread_state.h>
>  
>  #endif /* mach/x86/thread_state.h */
> -- 
> 2.40.1
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.