kevin@kosman.UUCP (Kevin O'Gorman) (09/07/89)
GCC 1.35 produces plausible but wrong output for some kinds of input. The problem is that the assembler 'space' pseudo-op is being used in the text segment, but this does not work. Sample input file (one line): > const char foo[40] = {0}; Invoking command: > gcc -v -S test.c console output: --- gcc version 1.35 /usr/local/lib/gcc-cpp -v -undef -D__GNUC__ -Dmc68k -Dunix -Dunixpc -D__mc68k__ -D__unix__ -D__unixpc__ test.c /tmp/cca12488.cpp GNU CPP version 1.35 /usr/local/lib/gcc-cc1 /tmp/cca12488.cpp -quiet -dumpbase test.c -version -o test.s GNU C version 1.35 (68k, SGS/AT&T unixpc syntax) compiled by GNU C version 1.35. --- Assembler file (6 lines): file "test.c" global foo text foo: byte 0 space 39 This is plausible but does not work right. I haven't tracked down the details, but the 'space' operation definitely does not work right in the 'text' context. It may be allocating space in the data segment, but I suspect that what's happening is that the space it allocates is not zeroed if it's in the text segment. What I got was two bytes of zeroes, and a bunch of bytes of something else (all the same: not too interesting.) You may call this a bug in the assembler, or in the loader, or whatever, but we're not likely to get new ones unless FSF provides them, so we're stuck... This emerged because of a particular usage in Nethack, which used a buffer of zeros to be written (under various casts, and with various lengths) to a save file. Using the -traditional switch makes Nethack #define const to nothing, so the whole thing appears in the data segment and the problem disappears, because foo is defined in the data segment.
andrew@frip.WV.TEK.COM (Andrew Klossner) (09/07/89)
Kevin O'Gorman (kevin@kosman.UUCP) reports that a "const" array
initialized to zero is translated to an assembly language "space"
pseudo-op in the text segment, and that the assembler allocates the
space but fills it with some non-zero value.
It's common for assemblers to satisfy a text "space" with no-op
instructions. GCC should not assume that "space" in the text segment
will generate zeros.
-=- Andrew Klossner (uunet!tektronix!frip.WV.TEK!andrew) [UUCP]
(andrew%frip.wv.tek.com@relay.cs.net) [ARPA]