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timer/nova: prevent potential division by zero

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This case triggered with the leitzentrale.run script on Qemu.
The frequency value must never initialized with zero.

Fixes #3663
This commit is contained in:
Norman Feske 2020-02-25 10:23:27 +01:00 committed by Christian Helmuth
parent 87cb10c558
commit daee1f4cb8
1 changed files with 14 additions and 5 deletions
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19
repos/base-nova/src/timer/nova/time_source.h
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@ -18,6 +18,7 @@
/* Genode includes */ /* Genode includes */
#include <trace/timestamp.h> #include <trace/timestamp.h>
#include <base/attached_rom_dataspace.h> #include <base/attached_rom_dataspace.h>
#include <base/log.h>
/* local includes */ /* local includes */
#include <threaded_time_source.h> #include <threaded_time_source.h>
@ -36,16 +37,24 @@ class Timer::Time_source : public Threaded_time_source
/* read the tsc frequency from platform info */ /* read the tsc frequency from platform info */
static unsigned long _obtain_tsc_khz(Genode::Env &env) static unsigned long _obtain_tsc_khz(Genode::Env &env)
{ {
unsigned long result = 0;
try { try {
Genode::Attached_rom_dataspace info { env, "platform_info"}; Genode::Attached_rom_dataspace info { env, "platform_info"};
return info.xml() result = info.xml().sub_node("hardware")
.sub_node("hardware") .sub_node("tsc")
.sub_node("tsc") .attribute_value("freq_khz", 0UL);
.attribute_value("freq_khz", 0UL);
} catch (...) { } } catch (...) { }
return 0; if (result)
return result;
/*
* The returned value must never be zero because it is used as
* divisor by '_tsc_to_us'.
*/
Genode::warning("unable to obtain tsc frequency, asuming 1 GHz");
return 1000*1000;
} }
Genode::addr_t _sem { ~0UL }; Genode::addr_t _sem { ~0UL };