Hi, [ As nobody answered, let's have a try. ] Le Wed, 3 May 2006 14:01:52 +0530, "srinivas bakki" <srinivas.bakki@xxxxxxxxx> a écrit : > somebody please help me understanding the following code. since > this code is referenced from setup.c how does the compiler put in > the physical address of the machine descriptor in r5 ? also this > address i dont understand why it is metioned as physical !!! First of all, you should have asked a more precise question, for example by telling us which file of the kernel you are copying below. (I've finally found that it's in arch/arm/kernel/head-common.S). I'm not an expert, but here's what happen: arch/arm/kernel/setup.c::setup_machine() calls lookup_machine_type(), defined in arch/arm/kernel/head-common.S. This lookup_machine_type() is basically a wrapper around __lookup_machine_type() that allows this function to be called from a C function by respecting the ARM C calling conventions. The lookup_machine_type() wrapper transfers the contents of r0 to r1, because the argument "nr" passed by the code in setup.c is stored in r0, but the __lookup_machine_type() function waits for the machine architecture number in r1. Then, the __lookup_machine_type() functions does its job (for which I can't help, as I'm not an ARM expert). Its job is to find a pointer to a certain structure, which is returned in r5. Once it has completed its job, control returns in lookup_machine_type(), which transfers the contents of r5 to r0. This is because r5 contains the actual result of the function, but the ARM C calling convention says that the return value must be stored in r0. Here is how it works between C and assembly. Now, if your question is how does __lookup_machine_type() work, then I suggest you to read some ARM architecture manual. Sincerly, Thomas -- PETAZZONI Thomas - thomas.petazzoni@xxxxxxxx http://{thomas,sos,kos}.enix.org - Jabber: thomas.petazzoni@xxxxxxxxx http://{agenda,livret}dulibre.org - http://www.toulibre.org Fingerprint : 0BE1 4CF3 CEA4 AC9D CC6E 1624 F653 CB30 98D3 F7A7
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