Hi,
The memory barrier routines are macros which calls a routine called
alternative, the call is something is like this : (for mb())
#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
can someone please help me understanding the alternative inline assembly, i am
finding it a bit confusing.
source is in : include/asm-i386/system.h
#define alternative(oldinstr, newinstr, feature) \
asm volatile ("661:\n\t" oldinstr "\n662:\n" \
".section .altinstructions,\"a\"\n" \
" .align 4\n" \
" .long 661b\n" /* label */ \
" .long 663f\n" /* new instruction */
\
" .byte %c0\n" /* feature bit */ \
" .byte 662b-661b\n" /* sourcelen */ \
" .byte 664f-663f\n" /* replacementlen */ \
".previous\n"
\
".section .altinstr_replacement,\"ax\"\n"
\
"663:\n\t" newinstr "\n664:\n" /* replacement */ \
".previous" :: "i" (feature) : "memory")
