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1899
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1 Installing ccache
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2 -----------------
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3
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4 The recommended way to use this with Debian is to either create "cc"
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5 and "gcc" symlinks to /usr/bin/ccache in your private bin directory
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6 (which must be before the real cc and gcc in your path), or use
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7 CC="ccache gcc" on the make command line.
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8
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9 Another option is to just prepend /usr/lib/ccache in your PATH
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10 environment variable, like
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11
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12 export PATH="/usr/lib/ccache:$PATH"
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13
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14 Note that ccache works with both native and cross compilers.
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15
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16 Ignoring whitespace
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17 -------------------
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18
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19 If you wish to set up ccache so that it ignores blank lines, have a
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20 look at the CCACHE_UNIFY option. However, please note that this
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21 option is off by default since the reported line numbers may not
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22 match the source files anymore.
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23
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24
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25 NFS Issues
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26 ----------
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27
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28 (from John Coiner <john.coiner@amd.com> on the ccache mailing list)
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29
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30 When CCache creates a hardlinked output file, it calls utime() to update
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31 the timestamp on the object, so that Make realizes that the object has
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32 changed.
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33
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34 On NFS, utime() has no coherency guarantee, AFAIK. When utime() runs on
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35 host A, and our parallel implementation of Make is running on host B,
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36 sometimes Make doesn't see the new timestamp soon enough -- and neglects
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37 to relink the final binary. That's a one-way ticket to Silent Mysterious
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38 Failure Town.
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39
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40 Instead of relying on the object file timestamp, we create a dummy file
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41 with a reliable timestamp:
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42
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43 objs/foo.o objs/foo.o.built :
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44 if ( ccache gcc -o foo.o -c foo.c ) ; \
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45 then touch objs/foo.o.built ; \
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46 else exit 1; \
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47 fi
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48
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49 binary : objs/foo.o.built
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50 gcc -o binary objs/foo.o
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51
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52 NFS does make a coherency guarantee, that if a file is written and
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53 close()d on host A, and subsequently open()ed on host B, that the second
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54 open() will reflect all modifications and attributes from the close().
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55 Since Make does open() when checking timestamps, and the dummy file is
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56 close()d when it's created, the binary will always relink after the
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57 object is recompiled.
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58
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59 -- Francois Marier <francois@debian.org> Sun, 20 May 2007 17:35:36 +1200
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