aux tables for PowerPC

From: Paul Mackerras (paulus@linuxcare.com.au)
Date: Sat Jun 10 2000 - 07:52:02 EDT

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    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.

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