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bdb4268928
area on VM stack to prevent SEGV on GC. GC may mark every value in VM stack. Unfortunately I couldn't write a test for it... So let me explain the situation. SEGV example: https://gist.github.com/k0kubun/c7cea2b5761ffdff29ec79ea1a8f7f91 ``` $ ruby --dump=insns -e 'def oct(num, len); "%0#{len}o" % num; end' == disasm: #<ISeq:oct@-e:1 (1,0)-(1,41)> (catch: FALSE) local table (size: 2, argc: 2 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1]) [ 2] num@0<Arg> [ 1] len@1<Arg> 0000 putobject "%0" ( 1)[LiCa] 0002 getlocal_WC_0 len@1 0004 dup 0005 checktype T_STRING 0007 branchif 14 0009 dup 0010 opt_send_without_block <callinfo!mid:to_s, argc:0, FCALL|ARGS_SIMPLE>, <callcache> 0013 tostring 0014 putobject "o" 0016 concatstrings 3 0018 getlocal_WC_0 num@0 0020 opt_mod <callinfo!mid:%, argc:1, ARGS_SIMPLE>, <callcache> 0023 leave [Re] ``` Prior to this commit, after arguments are pushed on 0010, stacks were: VM stack: [uninitialized, uninitialized, len] JIT stack: ["%0", len, len] And then, when GC is invoked on 0016, VM stack will be [uninitialized, uninitialized] and those uninitialized values will be marked by GC. With this commit, after arguments are pushed on 0010, stacks will be: VM stack: [len] JIT stack: ["%0", len, len] And VM stack will be [] on 0016. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e