On Sun, Feb 03, 2008 at 06:02:34PM +0000, Al Viro wrote: > On Sun, Feb 03, 2008 at 06:26:35PM +0100, Sam Ravnborg wrote: > > On Sun, Feb 03, 2008 at 01:08:44PM +0000, Al Viro wrote: > > > ; cat >a.c <<'EOF' > > > const char foo[] __attribute__ ((__section__(".blah"))) = ""; > > > const char * const bar __attribute__((__section__(".blah"))) = ""; > > > EOF > > > ; gcc -m32 -S a.c > > > ; gcc -m64 -S a.c > > > a.c:2: error: bar causes a section type conflict > > > ; > > > > > > That's 4.1.2 on ppc. What happens is that the second declaration > > > wants to make .blah writable. We actually trigger that in ppc64 > > > builds on drivers/net/natsemi.c. > > > > > > Note that on ppc64 without explicit sections you have the second one land > > > in > > > .data.rel.ro.local, which is "aw",progbits. > > > > > > The reason why it didn't visibly bite us before is that usually > > > __devinit... > > > just expanded to nothing (unless you disable HOTPLUG, which requires > > > EMBEDDED, which wasn't apparently common enough for ppc64 builds). > > > > > > Suggestions? > > > > Hi Al. > > > > __devinitconst were invented to cover this issue. > > So use __devinitconst for const data and > > __devinitdata for non-const data. > > As the example above shows, what is and what is not const data is > irrelevant. The data _is_ const. On ppc32 gcc is happy to put > it into read-only section. On ppc64 the same version of gcc insists > on making the section this data object is going to *writable*. > > > We recently had breakage in mainline with x86 64 bit > > (sis190) for the exact same case. > > No, this is not exact same case. Unfortunately. > > > Does this work in your ppc example or do we need > > to find another solution? > > Please, read the posted example. s/.blah/.devinit.rodata/ if you wish - it's > not magical. What happens is that > * gcc choice of r/o vs. r/w section is not determined by object > being const > * that choice is actually platform-dependent, even between related > platforms (see ppc32 and ppc64 in the example above).
Got it now - sorry. And I'm suprised to see that gcc thinks bar is writeable. If I try to assign it gcc error out as expected. To get your example building I had to kill the const in front of foo: char foo[] __attribute__ ((__section__(".blah"))) = ""; const char * const bar __attribute__((__section__(".blah"))) = ""; This is not an acceptable situation but for now I do not see a solution. It is as such not the __devinitconst thing that causes us problems here. It is the total concept of controlling the section of variables from our C-code base. We could invent a __initstr annotation but I dunno if that would suffice. Do you see any pattern when gcc do the r/w choice compared to the r/o choise. Maybe it is only const char[] that happens to be considered r/o and the rest is r/w? Should a gcc-bug be filed for this btw? Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/