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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") |
