path: root/arch/arm/kernel/perf_event.c
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authorUwe Kleine-König <u.kleine-koenig@pengutronix.de>2011-12-05 09:39:59 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2011-12-06 11:16:13 +0000
commitde66a979012dbc66b1ec0125795a3f79ee667b8a (patch)
tree078ddb11791244de56fb6271a6be11b5ce622907 /arch/arm/kernel/perf_event.c
parent974c07249b06d948154be3275bf4f6e55b585300 (diff)
ARM: 7187/1: fix unwinding for XIP kernels
The linker places the unwind tables in readonly sections. So when using an XIP kernel these are located in ROM and cannot be modified. For that reason the current approach to convert the relative offsets in the unwind index to absolute addresses early in the boot process doesn't work with XIP. The offsets in the unwind index section are signed 31 bit numbers and the structs are sorted by this offset. So it first has offsets between 0x40000000 and 0x7fffffff (i.e. the negative offsets) and then offsets between 0x00000000 and 0x3fffffff. When seperating these two blocks the numbers are sorted even when interpreting the offsets as unsigned longs. So determine the first non-negative entry once and track that using the new origin pointer. The actual bisection can then use a plain unsigned long comparison. The only thing that makes the new bisection more complicated is that the offsets are relative to their position in the index section, so the key to search needs to be adapted accordingly in each step. Moreover several consts are added to catch future writes and rename the member "addr" of struct unwind_idx to "addr_offset" to better match the new semantic. (This has the additional benefit of breaking eventual users at compile time to make them aware of the change.) In my tests the new algorithm was a tad faster than the original and has the additional upside of not needing the initial conversion and so saves some boot time and it's possible to unwind even earlier. Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Nicolas Pitre <nico@fluxnic.net> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel/perf_event.c')
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