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gcc. Per comment from original author, Brian Gallew: "Ancient history. Kill it fast."REL7_4_STABLE
Tom Lane
23 years ago
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<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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|
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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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|
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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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|
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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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|
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|
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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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|
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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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|
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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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|
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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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|
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</Chapter> |
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