Hi Maciej,
> Anyway, as noted above that shouldn't cause a problem with user software
> and I think that any corruption you can see comes from elsewhere. You'll
> have to paper this $ra non-sign-extension issue over somehow to proceed
> though.
I've extended do_IRQ with a register check under the condition that
user_mode(get_irq_regs()) is true, with the following sample results
where registers $2-$25 are printed if they are not sign-extended
properly (there is a certain amount of randomness to this):
$10 : 00005f6362696c5f
epc = 0fb6db00 in ld.so.1[fb60000+19000]
$8 : ffffff7272655f5f
$9 : ffffff7272655f5f
$10 : 7066732e6362696c
epc = 0fb759a0 in ld.so.1[fb60000+19000]
$10 : 7274735f65646f6d
$12 : ffff000000000000
$13 : 0000ffffffffffff
$14 : 000000ffffffffff
epc = 0fb6d03c in ld.so.1[fb60000+19000]
$10 : ffff732e6362696c
epc = 0fb6cfe8 in ld.so.1[fb60000+19000]
$8 : 000000ff00000000
epc = 77e29fe4 in libc.so.6[77dc0000+12e000]
$9 : 7fb71f357fb71f40
epc = 0041cc60 in busybox[400000+3d000]
$10 : 0000ffffff6f6c63
epc = 0fb6d060 in ld.so.1[fb60000+19000]
$10 : 00ffffffff657365
epc = 0fb6d03c in ld.so.1[fb60000+19000]
$12 : ffff000000000000
$13 : 0000ffffffffffff
epc = 0fb6d03c in ld.so.1[fb60000+19000]
$8 : 4700302e325f4342
$9 : 4700302e325f4342
$10 : 0000ff6e6769735f
$14 : 00ff000000000000
epc = 0fb75a6c in ld.so.1[fb60000+19000]
$10 : 635f6362696c5f5f
$12 : ffff000000000000
$13 : 0000ffffffffffff
epc = 0fb6d608 in ld.so.1[fb60000+19000]
I'm not yet sure this approach is completely correct, because there are
quite a few macros and other things to set this up, and I'm assuming all
these registers are saved for IRQs by SAVE_ALL. The regs variable is
64-bits unsigned long long and save/restore is SD/LD in relevant places.
It would be interesting to somehow single-step through BusyBox and for
every hardware instruction validate registers to find the first occurrence
where sign-extension breaks.
What about making the R5900 a 64-bit kernel only if it would turn out that
the 32-bit sign-extension logic is not completely reliable?
Fredrik
