Re: [Qemu-devel] [4691] PPC TCG Fixes

[malc]

On Sun, 8 Jun 2008, Thiemo Seufer wrote:

> malc wrote:
> > Revision: 4691
> >           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4691
> > Author:   malc
> > Date:     2008-06-07 20:31:33 +0000 (Sat, 07 Jun 2008)
> >
> > Log Message:
> > -----------
> > PPC TCG Fixes
> >
> > * Fix typo in aliased div2
> > * "Optimize" aliased div2/divu2
> > * Fix two remaining branch retranslation problems
> >   (Kudos to Andrzej Zaborowski)
> > * Rework goto_tb and set_jmp_target1
> > * Use correct size when flushing icache
> > * Use correct register selection for ORI
> >   (Was harmless since in both cases srcreg was equal to dstreg)
>
> FYI, the mips system emulation still crashes when executing the very
> first TB, apparently due to stack corruption. (This commit didn't
> change the behaviour.)

It's not a stack corruption it's a relocation problem, dyngen
relocates one of the calls inside (non tcged) op_mtc0_status as
R_PPC_REL24 but the signed displacement does not fit in 26 bits after
the code is placed into mmapped code_gen_buffer. Compiling op.o with
-mlongcall makes the emulation proceed much further, but then it still
crashes:

<transcript>
...
Inode-cache hash table entries: 2048 (order: 1, 8192 bytes)
Memory: 26964k/32768k available (2102k kernel code, 5804k reserved, 450k 
data, 132k init, 0k highmem)
Break instruction in kernel code[#1]:
...
Call Trace:
[<802a1788>] kmem_cache_init+0x160/0x434
[<8028f7f0>] start_kernel+0x1b8/0x2c0


Code: 26100001  1611fff4  00000000 <0200000d> 8e42002c  8fa80018  00031880 
0102001b  004001f4
Kernel panic - not syncing: Attempted to kill the idle task!

Perhaps something like this ought to be added to dyngen.c:
</transcript>

diff --git a/dyngen.c b/dyngen.c
index c38d123..69f4105 100644
--- a/dyngen.c
+++ b/dyngen.c
@@ -1963,6 +1963,11 @@ void gen_code(const char *name, host_ulong offset, 
host_ulong size,
                                 break;
                             case R_PPC_REL24:
                                 /* warning: must be at 32 MB distancy */
+                                fprintf(outfile, "{\n"
+                                        "    long disp = (%s - (long)(gen_code_ptr 
+ %d) + %d);\n"
+                                        "    if ((disp << 6) >> 6 != disp) abort 
();\n"
+                                        "}\n",
+                                        relname, reloc_offset, addend);
                                 fprintf(outfile, "    *(uint32_t *)(gen_code_ptr + %d) = 
(*(uint32_t *)(gen_code_ptr + %d) & ~0x03fffffc) | ((%s - (long)(gen_code_ptr + %d) + %d) 
& 0x03fffffc);\n",
                                         reloc_offset, reloc_offset, relname, 
reloc_offset, addend);
                                 break;

--
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