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Linus Torvalds
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Jul 25, 2011
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refs/heads/master: b6c2f86e6305be612f1196459f22343523f7049f | ||
refs/heads/master: ee05eff6f79c25617e5b7d7677b8f79d26abbe37 |
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On some architectures, when the kernel loads any userspace program it | ||
maps an ELF DSO into that program's address space. This DSO is called | ||
the vDSO and it often contains useful and highly-optimized alternatives | ||
to real syscalls. | ||
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These functions are called just like ordinary C function according to | ||
your platform's ABI. Call them from a sensible context. (For example, | ||
if you set CS on x86 to something strange, the vDSO functions are | ||
within their rights to crash.) In addition, if you pass a bad | ||
pointer to a vDSO function, you might get SIGSEGV instead of -EFAULT. | ||
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To find the DSO, parse the auxiliary vector passed to the program's | ||
entry point. The AT_SYSINFO_EHDR entry will point to the vDSO. | ||
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The vDSO uses symbol versioning; whenever you request a symbol from the | ||
vDSO, specify the version you are expecting. | ||
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Programs that dynamically link to glibc will use the vDSO automatically. | ||
Otherwise, you can use the reference parser in Documentation/vDSO/parse_vdso.c. | ||
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Unless otherwise noted, the set of symbols with any given version and the | ||
ABI of those symbols is considered stable. It may vary across architectures, | ||
though. | ||
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(As of this writing, this ABI documentation as been confirmed for x86_64. | ||
The maintainers of the other vDSO-using architectures should confirm | ||
that it is correct for their architecture.) |
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ROM-able zImage boot from eSD | ||
----------------------------- | ||
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An ROM-able zImage compiled with ZBOOT_ROM_SDHI may be written to eSD and | ||
SuperH Mobile ARM will to boot directly from the SDHI hardware block. | ||
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This is achieved by the mask ROM loading the first portion of the image into | ||
MERAM and then jumping to it. This portion contains loader code which | ||
copies the entire image to SDRAM and jumps to it. From there the zImage | ||
boot code proceeds as normal, uncompressing the image into its final | ||
location and then jumping to it. | ||
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This code has been tested on an mackerel board using the developer 1A eSD | ||
boot mode which is configured using the following jumper settings. | ||
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8 7 6 5 4 3 2 1 | ||
x|x|x|x| |x|x| | ||
S4 -+-+-+-+-+-+-+- | ||
| | | |x| | |x on | ||
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The eSD card needs to be present in SDHI slot 1 (CN7). | ||
As such S1 and S33 also need to be configured as per | ||
the notes in arch/arm/mach-shmobile/board-mackerel.c. | ||
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A partial zImage must be written to physical partition #1 (boot) | ||
of the eSD at sector 0 in vrl4 format. A utility vrl4 is supplied to | ||
accomplish this. | ||
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e.g. | ||
vrl4 < zImage | dd of=/dev/sdX bs=512 count=17 | ||
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A full copy of _the same_ zImage should be written to physical partition #1 | ||
(boot) of the eSD at sector 0. This should _not_ be in vrl4 format. | ||
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vrl4 < zImage | dd of=/dev/sdX bs=512 | ||
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Note: The commands above assume that the physical partition has been | ||
switched. No such facility currently exists in the Linux Kernel. | ||
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Physical partitions are described in the eSD specification. At the time of | ||
writing they are not the same as partitions that are typically configured | ||
using fdisk and visible through /proc/partitions |
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