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    SubjectRe: vdso.so mislinked by buggy linker was Re: Linus 2.6.23-rc1
    On Mon, Jul 23, 2007 at 01:56:20AM +0200, Andi Kleen wrote:
    > On Monday 23 July 2007 01:38:40 Andre Noll wrote:
    > [readded linux-kernel, Linus]
    >
    > > [Nr] Name Type Address Offset
    > > Size EntSize Flags Link Info Align
    > > [ 0] NULL 0000000000000000 00000000
    > > 0000000000000000 0000000000000000 0 0 0
    > > [ 1] .hash HASH ffffffffff700120 00000120
    > > 00000000000000b4 0000000000000004 A 2 0 8
    > > [ 2] .dynsym DYNSYM ffffffffff7001d8 000001d8
    > > 0000000000000270 0000000000000018 A 3 12 8
    > > [ 3] .dynstr STRTAB ffffffffff700448 00000448
    > > 0000000000000059 0000000000000000 A 0 0 1
    > > [ 4] .gnu.version VERSYM ffffffffff7004a2 000004a2
    > > 0000000000000034 0000000000000002 A 2 0 2
    > > [ 5] .gnu.version_d VERDEF ffffffffff7004d8 000004d8
    > > 0000000000000038 0000000000000000 A 3 2 8
    > > [ 6] .text PROGBITS ffffffffff700c00 00100bab
    > ^^^^^^^^
    > > 00000000000002e4 0000000000000000 AX 0 0 64
    >
    > It puts .text at 1MB. Your vdso file must be huge?
    >
    > It looks like it ignores the
    > -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
    > options passed to it. The AMD64 ABI has a 1MB minimum page size, but
    > these options are supposed to disable it.
    >
    > Not sure how to work around this, but having an 1+MB vdso would be incredibly
    > wasteful. What version is it? Perhaps we just drop support for this. I can't
    > think of a workaround currently.

    Looking at vdso.lds.S, if you change just VDSO_TEXT_OFFSET to 0xc00 and
    don't tweak the linker script, then you jump backwards with the dot, you
    should even get a linker warning about it:

    . = VDSO_PRELINK + VDSO_TEXT_OFFSET;

    .text : { *(.text) } :text
    .text.ptr : { *(.text.ptr) } :text
    . = VDSO_PRELINK + 0x900;

    Guess that 0x900 should have been VDSO_TEXT_OFFSET + 0x400 or something
    similar. Also note that it is highly desirable to fit the whole vdso into
    one page, so increasing VDSO_TEXT_OFFSET etc. offsets too much is just
    wasting memory. From the above dump, VDSO_TEXT_OFFSET 0x500 is too low,
    but 0x600 should work, assuming .data section is moved 0x100 higher as well.

    Jakub
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