1 --- md.h 2009-10-01 20:46:43.000000000 +0200 2 +++ md.h 2014-12-16 22:52:34.000000000 +0100 3 @@ -161,6 +161,19 @@ 4 #define MD_JB_SP 34 5 #elif defined(__amd64__) 6 #define MD_JB_SP 2 7 +/* 8 + * The following comment is taken from src/lib/libc/amd64/gen/makecontext.c 9 + * It explains why we specifically break the alignment to 64 byte boundary 10 + * that is unconditionally enforced by sched.c, by setting MD_STACK_PAD_SIZE 11 + * to this funky value. 12 + * Without this, anything using va_start() & friends fails unpredictably. 13 + */ 14 + /* 15 + * Account for arguments on stack and do the funky C entry alignment. 16 + * This means that we need an 8-byte-odd alignment since the ABI expects 17 + * the return address to be pushed, thus breaking the 16 byte alignment. 18 + */ 19 +#define MD_STACK_PAD_SIZE 8 20 #else 21 #error Unknown CPU architecture 22 #endif 23