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The existence of MMX and SSE is required by the System V x86_64 ABI
and so is assumed by gcc, but these registers are not preserved by our
own interrupt handlers and are unlikely to be preserved by other
context switch handlers in a boot firmware environment.
Explicitly prevent gcc from using MMX or SSE registers to avoid
potential problems due to silent register corruption.
We must remove the %xmm0-%xmm5 clobbers from the x86_64 version of
hv_call() since otherwise gcc will complain about unknown register
names. Theoretically, we should probably add code to explicitly
preserve the %xmm0-%xmm5 registers across a hypercall, in order to
guarantee to external code that these registers remain unchanged. In
practice this is difficult since SSE registers are disabled by
default: for background information see commits 71560d1 ("[librm]
Preserve FPU, MMX and SSE state across calls to virt_call()") and
dd9a14d ("[librm] Conditionalize the workaround for the Tivoli VMM's
SSE garbling").
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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The bulk of the iPXE binary (the .textdata section) is physically
relocated at runtime to the top of the 32-bit address space in order
to allow space for an OS to be loaded. The relocation is achieved
with the assistance of segmentation: we adjust the code and data
segment bases so that the link-time addresses remain valid.
Segmentation is not available (for normal code and data segments) in
long mode. We choose to compile the C code with -mcmodel=kernel and
use a link-time address of 0xffffffffeb000000. This choice allows us
to identity-map the entirety of the 32-bit address space, and to alias
our chosen link-time address to the physical location of our .textdata
section. (This requires the .textdata section to always be aligned to
a page boundary.)
We simultaneously choose to set the 32-bit virtual address segment
bases such that the link-time addresses may simply be truncated to 32
bits in order to generate a valid 32-bit virtual address. This allows
symbols in .textdata to be trivially accessed by both 32-bit and
64-bit code.
There is no (sensible) way in 32-bit assembly code to generate the
required R_X86_64_32S relocation records for these truncated symbols.
However, subtracting the fixed constant 0xffffffff00000000 has the
same effect as truncation, and can be represented in a standard
R_X86_64_32 relocation record. We define the VIRTUAL() macro to
abstract away this truncation operation, and apply it to all
references by 32-bit (or 16-bit) assembly code to any symbols within
the .textdata section.
We define "virt_offset" for a 64-bit build as "the value to be added
to an address within .textdata in order to obtain its physical
address". With this definition, the low 32 bits of "virt_offset" can
be treated by 32-bit code as functionally equivalent to "virt_offset"
in a 32-bit build.
We define "text16" and "data16" for a 64-bit build as the physical
addresses of the .text16 and .data16 sections. Since a physical
address within the 32-bit address space may be used directly as a
64-bit virtual address (thanks to the identity map), this definition
provides the most natural access to variables in .text16 and .data16.
Note that this requires a minor adjustment in prot_to_real(), which
accesses .text16 using 32-bit virtual addresses.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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None of the x86_64 builds currently have any way of invoking these
functions. They are included only to avoid introducing unnecessary
architecture-specific dependencies into the self-test suite.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Current versions of gcc require -maccumulate-outgoing-args if any
sysv_abi functions call ms_abi functions. This requirement is likely
to be lifted in future gcc versions, so test explicitly to see if the
current version of gcc requires -maccumulate-outgoing-args.
This problem is currently masked since the implied
-fasynchronous-unwind-tables (which is the default in current gcc
versions) implies -maccumulate-outgoing-args.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Currently the only supported platform for x86_64 is EFI.
Building an EFI64 gPXE requires a version of gcc that supports
__attribute__((ms_abi)). This currently means a development build of
gcc; the feature should be present when gcc 4.4 is released.
In the meantime; you can grab a suitable gcc tree from
git://git.etherboot.org/scm/people/mcb30/gcc/.git
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