It turns out that glibc on the PowerPC needs to know the cache line
size (the reason is so that it can use the dcbz instruction safely;
dcbz clears an entire cache line to zero and marks it as modified,
without generating a read to the cache line from memory).
The Sys V ABI for the PowerPC defines three entries which should be
put in the auxiliary table when the system starts an executable:
AT_DCACHEBSIZE, AT_ICACHEBSIZE and AT_UCACHEBSIZE, giving the data,
instruction, and unified cache block (line) sizes. (The
AT_UCACHEBSIZE value would be zero on systems with unified caches).
These three tags are assigned the numbers 10, 11, 12 in the PowerPC
Sys V ABI. Unfortunately these numbers are assigned to AT_NOTELF,
AT_UID and AT_EUID in include/linux/elf.h, and AT_UID and AT_EUID are
actually used in fs/binfmt_elf.c.
So on PowerPC we want to put in AT_*CACHEBSIZE entries but if we do,
we'll end up with two different entries with tag 11, likewise with 12.
Does anyone know where the numbers for AT_NOTELF, AT_UID and AT_EUID
come from? Are they just arbitrarily assigned in the linux source or
do they come from some standard, e.g. posix or something?
Thanks,
Paul.
-- Paul Mackerras, Senior Open Source Researcher, Linuxcare, Inc. +61 2 6262 8990 tel, +61 2 6262 8991 fax paulus@linuxcare.com.au, http://www.linuxcare.com.au/ Linuxcare. Support for the revolution.- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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