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a2c1d73b94
Currently the kernel Image is stripped of everything past the initial stack, and at runtime the memory is initialised and used by the kernel. This makes the effective minimum memory footprint of the kernel larger than the size of the loaded binary, though bootloaders have no mechanism to identify how large this minimum memory footprint is. This makes it difficult to choose safe locations to place both the kernel and other binaries required at boot (DTB, initrd, etc), such that the kernel won't clobber said binaries or other reserved memory during initialisation. Additionally when big endian support was added the image load offset was overlooked, and is currently of an arbitrary endianness, which makes it difficult for bootloaders to make use of it. It seems that bootloaders aren't respecting the image load offset at present anyway, and are assuming that offset 0x80000 will always be correct. This patch adds an effective image size to the kernel header which describes the amount of memory from the start of the kernel Image binary which the kernel expects to use before detecting memory and handling any memory reservations. This can be used by bootloaders to choose suitable locations to load the kernel and/or other binaries such that the kernel will not clobber any memory unexpectedly. As before, memory reservations are required to prevent the kernel from clobbering these locations later. Both the image load offset and the effective image size are forced to be little-endian regardless of the native endianness of the kernel to enable bootloaders to load a kernel of arbitrary endianness. Bootloaders which wish to make use of the load offset can inspect the effective image size field for a non-zero value to determine if the offset is of a known endianness. To enable software to determine the endinanness of the kernel as may be required for certain use-cases, a new flags field (also little-endian) is added to the kernel header to export this information. The documentation is updated to clarify these details. To discourage future assumptions regarding the value of text_offset, the value at this point in time is removed from the main flow of the documentation (though kept as a compatibility note). Some minor formatting issues in the documentation are also corrected. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Tom Rini <trini@ti.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Kevin Hilman <kevin.hilman@linaro.org> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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