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Still haven't found a stack diagram of what Linux hands over to a signal handler. What I've managed to piece together, possibly accurately, is this (offsets indicate dwords, multiply by 4 for byte offset):

Offset   Contents          Example
0        return addr       0x0fffe420
1        signal number     0xb (11=segfault)
2        GS (?)            0 (start of interrupted task's registers)
3        FS (?)            0
4        ES (?)            0x7b
5        DS (?)            0x7b
6        EDI               0x08088000
7        ESI               0
8        EBP               0
9        ESP               0xbffffcbc
10       EBX               2
11       EDX               0xc
12       ECX               0x10
13       EAX               0xa
14       ?                 0xe
15       ?                 4
16       addr that faulted 0x08048131  (rep scasb)
17       CS (?)            0x73
18       eflags            0x00010206
19       ESP               0xbffffcbc
20       SS                0x7b

The signal number is also provided in EAX. All the above registers, including the flags and return address, can be modified by the handler. Very ugly and nonportable, but magical in its possibilities.

My brilliant idea of speeding up I/O using memory protection and signal handling failed. I still believe it has possibilities, but I need to find a way to profile what's going on.

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last updated 2009-11-01 04:26:45. served from tektonic