78 lines
2.1 KiB
Plaintext
78 lines
2.1 KiB
Plaintext
<Chapter Id="compiler">
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<DocInfo>
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<AuthorGroup>
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<Author>
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<FirstName>Brian</FirstName>
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<Surname>Gallew</Surname>
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</Author>
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</AuthorGroup>
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<Date>Transcribed 1998-02-12</Date>
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</DocInfo>
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<Title><application>gcc</application> Default Optimizations</Title>
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<Para>
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<Note>
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<Para>
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Contributed by Brian Gallew (<email>geek+@cmu.edu</email>)
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</Para>
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</Note>
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</para>
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<Para>
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Configuring gcc to use certain flags by default is a simple matter of
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editing the
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<FileName>/usr/local/lib/gcc-lib/<Replaceable>platform</Replaceable>/<Replaceable>version</Replaceable>/specs</FileName>
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file.
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The format of this file pretty simple. The file is broken into
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sections, each of which is three lines long. The first line is
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"*<Replaceable>section_name</Replaceable>:" (e.g. "*asm:").
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The second line is a list of flags,
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and the third line is blank.
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</para>
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<Para>
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The easiest change to make is to append
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the desired default flags to the list in the appropriate section. As
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an example, let's suppose that I have linux running on a '486 with gcc
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2.7.2 installed in the default location. In the file
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/usr/local/lib/gcc-lib/i486-linux/2.7.2/specs, 13 lines down I find
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the following section:
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<ProgramListing>
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- ----------SECTION----------
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*cc1:
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- ----------SECTION----------
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</ProgramListing>
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As you can see, there aren't any default flags. If I always wanted
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compiles of C code to use "-m486 -fomit-frame-pointer", I would
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change it to look like:
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<ProgramListing>
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- ----------SECTION----------
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*cc1:
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- -m486 -fomit-frame-pointer
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- ----------SECTION----------
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</ProgramListing>
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If I wanted to be able to generate 386 code for another, older linux
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box lying around, I'd have to make it look like this:
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<ProgramListing>
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- ----------SECTION----------
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*cc1:
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%{!m386:-m486} -fomit-frame-pointer
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- ----------SECTION----------
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</ProgramListing>
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This will always omit frame pointers, any will build 486-optimized
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code unless -m386 is specified on the command line.
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</para>
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<Para>
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You can actually do quite a lot of customization with the specs file.
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Always remember, however, that these changes are global, and affect
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all users of the system.
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</para>
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</Chapter>
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