------- Comment #18 from s_j_newbury at yahoo dot co dot uk 2007-08-03 12:56
-------
(In reply to comment #17)
> Re comment #16: I've tested this, and it seems to work. What failures do you
> expect?
>
/* How to make a trampoline. */
#define FFI_INIT_TRAMPOLINE(TRAMP,FUN,CTX) \
({ unsigned char *__tramp = (unsigned char*)(TRAMP); \
unsigned int __fun = (unsigned int)(FUN); \
unsigned int __ctx = (unsigned int)(CTX); \
*(unsigned int*) &__tramp[0] = 0xe92d000f; /* stmfd sp!, {r0-r3} */ \
*(unsigned int*) &__tramp[4] = 0xe59f0000; /* ldr r0, [pc] */ \
*(unsigned int*) &__tramp[8] = 0xe59ff000; /* ldr pc, [pc] */ \
*(unsigned int*) &__tramp[12] = __ctx; \
*(unsigned int*) &__tramp[16] = __fun; \
register unsigned long _beg __asm ("a1") = (unsigned long) (&__tramp[0]);
\
register unsigned long _end __asm ("a2") = (unsigned long) (&__tramp[19]);
\
register unsigned long _flg __asm ("a3") = 0; \
__asm __volatile ("swi\ 0x9f0002 @ sys_cacheflush" \
: "=r" (_beg) \
: "0" (_beg), "r" (_end), "r" (_flg)); \
})
The above swi uses the OABI syscall base.
>From include/asm-arm/unistd.h:
#define __NR_OABI_SYSCALL_BASE 0x900000
#if defined(__thumb__) || defined(__ARM_EABI__)
#define __NR_SYSCALL_BASE 0
#else
#define __NR_SYSCALL_BASE __NR_OABI_SYSCALL_BASE
#endif
With EABI all syscalls are called as swi 0 with the syscall number passed in a
register rather than encoding it into the instruction (offset from 0x900000).
When the above code from ffi.c is executed on a kernel lacking the OABI syscall
handling it will fail with an illegal instruction trap.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31325
