well, this was a fun little bug. i downloaded bison and within a few minutes i'd narrowed the problem down to lib/c-ctype.h. and it only took another minute to isolate this as the problem statement.
#if (' ' == 32) && ('!' == 33) && ('"' == 34) && ('#' == 35) \ && ('%' == 37) && ('&' == 38) && ('\'' == 39) && ('(' == 40) \ && (')' == 41) && ('*' == 42) && ('+' == 43) && (',' == 44) \ && ('-' == 45) && ('.' == 46) && ('/' == 47) && ('0' == 48) \ && ('1' == 49) && ('2' == 50) && ('3' == 51) && ('4' == 52) \ && ('5' == 53) && ('6' == 54) && ('7' == 55) && ('8' == 56) \ && ('9' == 57) && (':' == 58) && (';' == 59) && ('<' == 60) \ && ('=' == 61) && ('>' == 62) && ('?' == 63) && ('A' == 65) \ && ('B' == 66) && ('C' == 67) && ('D' == 68) && ('E' == 69) \ && ('F' == 70) && ('G' == 71) && ('H' == 72) && ('I' == 73) \ && ('J' == 74) && ('K' == 75) && ('L' == 76) && ('M' == 77) \ && ('N' == 78) && ('O' == 79) && ('P' == 80) && ('Q' == 81) \ && ('R' == 82) && ('S' == 83) && ('T' == 84) && ('U' == 85) \ && ('V' == 86) && ('W' == 87) && ('X' == 88) && ('Y' == 89) \ && ('Z' == 90) && ('[' == 91) && ('\\' == 92) && (']' == 93) \ && ('^' == 94) && ('_' == 95) && ('a' == 97) && ('b' == 98) \ && ('c' == 99) && ('d' == 100) && ('e' == 101) && ('f' == 102) \ && ('g' == 103) && ('h' == 104) && ('i' == 105) && ('j' == 106) \ && ('k' == 107) && ('l' == 108) && ('m' == 109) && ('n' == 110) \ && ('o' == 111) && ('p' == 112) && ('q' == 113) && ('r' == 114) \ && ('s' == 115) && ('t' == 116) && ('u' == 117) && ('v' == 118) \ && ('w' == 119) && ('x' == 120) && ('y' == 121) && ('z' == 122) \ && ('{' == 123) && ('|' == 124) && ('}' == 125) && ('~' == 126) /* The character set is ASCII or one of its variants or extensions, not EBCDIC. Testing the value of '\n' and '\r' is not relevant. */ #define C_CTYPE_ASCII 1 #endif from there, the problem was pretty easy to spot NSTAK was too small, and unguarded. the funny "+ 1" is to allow for a few operators that can add 2 to the stack in one trip through the loop. ; diffy -c eval.c /n/dump/2011/0725/sys/src/cmd/cpp/eval.c:2,8 - eval.c:2,8 #include <libc.h> #include "cpp.h" - #define NSTAK 32 + #define NSTAK 1024 #define SGN 0 #define UNS 1 #define UND 2 /n/dump/2011/0725/sys/src/cmd/cpp/eval.c:92,99 - eval.c:92,99 int evalop(struct pri); struct value tokval(Token *); - struct value vals[NSTAK], *vp; - enum toktype ops[NSTAK], *op; + struct value vals[NSTAK + 1], *vp; + enum toktype ops[NSTAK + 1], *op; /* * Evaluate an #if #elif #ifdef #ifndef line. trp->tp points to the keyword. /n/dump/2011/0725/sys/src/cmd/cpp/eval.c:122,127 - eval.c:122,129 op = ops; *op++ = END; for (rand=0, tp = trp->bp+ntok; tp < trp->lp; tp++) { + if(op >= ops + NSTAK) + sysfatal("cpp: can't evalute #if: increase NSTAK"); switch(tp->type) { case WS: case NL: - erik