device: add fudge factor for handle padding
When CONFIG_USERSPACE is enabled, the ELF file from linker pass 1 is used to create a hash table that identifies kernel objects by address. We therefore can't allow the size of any object in the pass 2 ELF to change in a way that would change those addresses, or we would create a garbage hash table. Simultaneously (and regardless of CONFIG_USERSPACE's value), gen_handles.py must transform arrays of handles from their pass 1 values to their pass 2 values; see the file's docstring for more details on that transformation. The way this works is that gen_handles.py just pads out each pass 2 array so its length is the same as its pass 1 value. The padding value is a repeated run of DEVICE_HANDLE_ENDS values. This value is the terminator which we look for at runtime in places like device_required_handles_get(), so there must be at least one, and we error out in gen_handles.py if there's no room in the pass 2 array for at least one such value. (If there is extra room, we just keep inserting extra DEVICE_HANDLE_ENDS values to pad the array to its original length.) However, it is possible that a device has more direct dependencies in the pass 2 handles array than its corresponding devicetree node had in the pass 1 array. When this happens, users have no recourse, so that's a potential showstopper. To work around this possibility for now, add a new config option, CONFIG_DEVICE_HANDLE_PADDING, whose value defaults to 0. When nonzero, it is a count of padding handles that are inserted into each device handles array. When gen_handles.py errors out due to lack of room, its error message now tells the user how much to increase CONFIG_DEVICE_HANDLE_PADDING by to work around the problem. It looks like a real fix for this is to allocate kernel objects whose addresses are required for hash tables in CONFIG_USERSPACE=y configurations *before* the handle arrays. The handle arrays could then be resized as needed in pass 2, which saves ROM by avoiding unnecessary padding, and would avoid the need for CONFIG_DEVICE_HANDLE_PADDING altogether. However, this 'real fix' is not available and we are facing a deadline to get a temporary solution in for Zephyr v2.7.0, so this is a good enough workaround for now. Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
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3 changed files with 69 additions and 2 deletions
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@ -699,6 +699,50 @@ static inline bool device_is_ready(const struct device *dev)
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Z_DEVICE_STATE_DEFINE(node_id, dev_name) \
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Z_DEVICE_DEFINE_PM_SLOT(dev_name)
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/* Helper macros needed for CONFIG_DEVICE_HANDLE_PADDING. These should
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* be deleted when that option is removed.
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*
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* This is implemented "by hand" -- rather than using a helper macro
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* like UTIL_LISTIFY() -- because we need to allow users to wrap
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* DEVICE_DT_DEFINE with UTIL_LISTIFY, like this:
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*
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* #define DEFINE_FOO_DEVICE(...) DEVICE_DT_DEFINE(...)
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* UTIL_LISTIFY(N, DEFINE_FOO_DEVICE)
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*
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* If Z_DEVICE_HANDLE_PADDING uses UTIL_LISTIFY, this type of code
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* would fail, because the UTIL_LISTIFY token within the
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* Z_DEVICE_DEFINE_HANDLES expansion would not be expanded again,
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* since it appears in a context where UTIL_LISTIFY is already being
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* expanded. Standard C does not reexpand macros appearing in their
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* own expansion; this would lead to infinite recursions in general.
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*/
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#define Z_DEVICE_HANDLE_PADDING \
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Z_DEVICE_HANDLE_PADDING_(CONFIG_DEVICE_HANDLE_PADDING)
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#define Z_DEVICE_HANDLE_PADDING_(count) \
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Z_DEVICE_HANDLE_PADDING__(count)
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#define Z_DEVICE_HANDLE_PADDING__(count) \
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Z_DEVICE_HANDLE_PADDING_ ## count
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#define Z_DEVICE_HANDLE_PADDING_10 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_9
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#define Z_DEVICE_HANDLE_PADDING_9 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_8
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#define Z_DEVICE_HANDLE_PADDING_8 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_7
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#define Z_DEVICE_HANDLE_PADDING_7 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_6
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#define Z_DEVICE_HANDLE_PADDING_6 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_5
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#define Z_DEVICE_HANDLE_PADDING_5 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_4
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#define Z_DEVICE_HANDLE_PADDING_4 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_3
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#define Z_DEVICE_HANDLE_PADDING_3 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_2
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#define Z_DEVICE_HANDLE_PADDING_2 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_1
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#define Z_DEVICE_HANDLE_PADDING_1 \
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DEVICE_HANDLE_ENDS, Z_DEVICE_HANDLE_PADDING_0
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#define Z_DEVICE_HANDLE_PADDING_0 EMPTY
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/* Initial build provides a record that associates the device object
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* with its devicetree ordinal, and provides the dependency ordinals.
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@ -735,6 +779,7 @@ BUILD_ASSERT(sizeof(device_handle_t) == 2, "fix the linker scripts");
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)) \
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DEVICE_HANDLE_SEP, \
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Z_DEVICE_EXTRA_HANDLES(__VA_ARGS__) \
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Z_DEVICE_HANDLE_PADDING \
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};
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#ifdef CONFIG_PM_DEVICE
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@ -303,6 +303,22 @@ config WAITQ_DUMB
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endchoice # WAITQ_ALGORITHM
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config DEVICE_HANDLE_PADDING
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int "Number of additional device handles to use for padding"
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default 0
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range 0 10
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help
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This is a "fudge factor" which works around build system
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limitations. It is safe to ignore unless you get a specific
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build system error about it.
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The option's value is the number of superfluous device handle
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values which are introduced into the array pointed to by each
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device's 'handles' member during the first linker pass.
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Each handle uses 2 bytes, so a value of 3 would use an extra
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6 bytes of ROM for every device.
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menu "Kernel Debugging and Metrics"
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config INIT_STACKS
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@ -311,9 +311,15 @@ def main():
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# address. We can't allow the size of any object in the
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# final elf to change. We also must make sure at least one
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# DEVICE_HANDLE_ENDS is inserted.
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assert len(hdls) < len(hs.handles), "%s no DEVICE_HANDLE_ENDS inserted" % (dev.sym.name,)
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while len(hdls) < len(hs.handles):
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padding = len(hs.handles) - len(hdls)
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assert padding > 0, \
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(f"device {dev.sym.name}: "
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"linker pass 1 left no room to insert DEVICE_HANDLE_ENDS. "
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"To work around, increase CONFIG_DEVICE_HANDLE_PADDING by " +
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str(1 + (-padding)))
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while padding > 0:
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hdls.append(DEVICE_HANDLE_ENDS)
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padding -= 1
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assert len(hdls) == len(hs.handles), "%s handle overflow" % (dev.sym.name,)
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lines = [
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