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[Bug gold/20642] internal error in get_section_contents, at icf.cc:467 w

From: ccoutant at gmail dot com
Subject: [Bug gold/20642] internal error in get_section_contents, at icf.cc:467 with --icf=safe
Date: Wed, 25 Apr 2018 00:53:56 +0000


--- Comment #14 from Cary Coutant <ccoutant at gmail dot com> ---
> It boils down to reading a character 'c' off the string and then translating 
> it
> through a lookup table to a UTF-16 code point:
>     private static immutable dchar m_charMapStart = 0xa1;
>     private static immutable dchar m_charMapEnd = 0xff;
>     private immutable wstring charMap =
>         "\u0104\u02D8\u0141\u00A4\u013D\u015A\u00A7\u00A8"~
>         "\u0160\u015E\u0164\u0179\u00AD\u017D\u017B\u00B0"~
>         "\u0105\u02DB\u0142\u00B4\u013E\u015B\u02C7\u00B8"~
>         "\u0161\u015F\u0165\u017A\u02DD\u017E\u017C\u0154"~
>         "\u00C1\u00C2\u0102\u00C4\u0139\u0106\u00C7\u010C"~
>         "\u00C9\u0118\u00CB\u011A\u00CD\u00CE\u010E\u0110"~
>         "\u0143\u0147\u00D3\u00D4\u0150\u00D6\u00D7\u0158"~
>         "\u016E\u00DA\u0170\u00DC\u00DD\u0162\u00DF\u0155"~
>         "\u00E1\u00E2\u0103\u00E4\u013A\u0107\u00E7\u010D"~
>         "\u00E9\u0119\u00EB\u011B\u00ED\u00EE\u010F\u0111"~
>         "\u0144\u0148\u00F3\u00F4\u0151\u00F6\u00F7\u0159"~
>         "\u016F\u00FA\u0171\u00FC\u00FD\u0163\u02D9";
>     return (c >= m_charMapStart && c <= m_charMapEnd) ?
> charMap[c-m_charMapStart] : c;
> There is a safety range check in place here. That's where the "cmp
> $0x5e,%ecx" comes from in the assembly before the table 'charMap' is indexed
> and the heuristic fails.

Aha! And 0x142 == m_charMapStart * sizeof(wchar). So it's just folding
the index computation into the base address.


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