On Sat, Feb 14, 2004 at 03:17:40AM +0100, Thiemo Seufer wrote: > Ralf Baechle wrote: > [snip] > > Anyway, gcc could load next weeks lucky lottery numbers into the > > s-registers after saving them. That'd break save_static but not the > > ABI which only promises to restore the old values in s-registers on > > return. > > Ok, it could, but adding such insns to the prologue wouldn't make > sense at all, so this is unlikely to happen. > OS people who have been around long enough know "unlikely" things always end up happening. :) See my posting around Oct 2000 below. Granted - gcc has changed a lot and perhaps it won't do it again. But just like a Chinese saying, "Once bitten by the snake, afraid of the straw rope for three years". :) I like the safe alternative. Jun P.S., the actual fix was done by Ralf http://www.linux-mips.org/xcvs/linux-mips/patches/001282_001027_MAIN_ralf ------------------------------------------------------------------ Nasty degree - 3 days of tracking. The symptom was pthread cannot be created. In the end the caller will get a BUS error. What exactly happened has to do with how registers are saved. Below attached is the beginning part of sys_sigsuspend() function. It is easy to see that s0 is saved into stack frame AFTER its modified. Next time when process returns to userland, the s0 reg will be wrong! So the bug is either 1) that we need to save s0 register in SAVE_SOME and not save it in save_static; or that 2) we fix compiler so that it does not use s0 register in that case (it does the same thing for sys_rt_sigsuspend) I am sure Ralf will have something to say about it. :-) In any case, I attached a patch for 1) fix. Jun ------------ sys_sigsuspend(struct pt_regs regs) { 8008e280: 27bdffc0 addiu $sp,$sp,-64 8008e284: afb00030 sw $s0,48($sp) sigset_t *uset, saveset, newset; save_static(®s); 8008e288: 27b00040 addiu $s0,$sp,64 8008e28c: afbf003c sw $ra,60($sp) 8008e290: afb20038 sw $s2,56($sp) 8008e294: afb10034 sw $s1,52($sp) 8008e298: afa40040 sw $a0,64($sp) 8008e29c: afa50044 sw $a1,68($sp) 8008e2a0: afa60048 sw $a2,72($sp) 8008e2a4: afa7004c sw $a3,76($sp) 8008e2a8: ae100058 sw $s0,88($s0) 8008e2ac: ae11005c sw $s1,92($s0) .....
