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    SubjectRe: non-modular 2.6 ppc kernels miscompiled by gcc-3.3.1?
    On Sun, 12 Oct 2003 15:19:22 +0200, Benjamin Herrenschmidt wrote:
    >On Sun, 2003-10-12 at 15:10, Mikael Pettersson wrote:
    >> When I compile a non-modular 2.6 kernel for ppc with gcc-3.3.1,
    >> it oopses in __copy_tofrom_user() [copy_mount_options()] in
    >> user-space's first mount /proc call. User-space limps along
    >> for a while, oopsing in every mount call, and then hangs.
    >>
    >> This occurs with 2.6.0-test5, test6, and the test7-based
    >> linuxppc-2.5 tree (rsync:ed today).
    >>
    >> Enabling CONFIG_MODULES=y but still keeping everything built-in
    >> prevents the oopses.
    >
    >Smells like some section alignement issues. Can you check
    >how the __ex_table section is aligned and where __start___ex_table
    >points to ? (using objdump)

    You're right, it turned out to be an alignment issue. Here's what
    my System.map looks like with gcc-3.3.1 and CONFIG_MODULES=n:

    c017ba4d ? __start___kcrctab
    c017ba4d ? __start___kcrctab_gpl
    c017ba4d ? __start___ksymtab
    c017ba4d ? __start___ksymtab_gpl
    c017ba4d ? __stop___kcrctab
    c017ba4d ? __stop___kcrctab_gpl
    c017ba4d ? __stop___ksymtab
    c017ba4d ? __stop___ksymtab_gpl
    c017ba4d A __start___ex_table
    c017cf08 A __start___bug_table
    c017cf08 A __stop___ex_table
    c01801c8 A __stop___bug_table

    Notice __start___ex_table[]'s address: it's not 4-byte aligned.
    With gcc-3.2.3 it got an 8-byte aligned address in my 2.6 kernel.

    vmlinux.lds.S doesn't explicitly align __start___ex_table, so I
    simply put ". = ALIGN(4);" before it and Voila! now it works.

    /Mikael

    --- linuxppc-2.5/arch/ppc/kernel/vmlinux.lds.S.~1~ 2003-09-28 12:19:36.000000000 +0200
    +++ linuxppc-2.5/arch/ppc/kernel/vmlinux.lds.S 2003-10-12 21:16:24.121283928 +0200
    @@ -47,6 +47,7 @@

    .fixup : { *(.fixup) }

    + . = ALIGN(4);
    __start___ex_table = .;
    __ex_table : { *(__ex_table) }
    __stop___ex_table = .;
    -
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