Re: [Qemu-devel] Could configure generate QEMU's linker scripts?

[Claudio Fontana <claudio.fontana@huawei.com>]

On 03.06.2013 16:57, Peter Maydell wrote:
> On 3 June 2013 15:23, Richard Henderson <rth@twiddle.net> wrote:
>> On 06/02/2013 10:15 AM, Peter Maydell wrote:
>>> So for a new architecture how do we determine whether we need
>>> to fiddle with the start address or not? (More specifically,
>>> is aarch64 going to need a linker script or just to go in the
>>> configure list of "hosts which don't need one" ?)
>>
>> Basically, for a non-PIE build, is there room to run the
>> -linux-user guest binary?  That means getting out of the
>> way of the guest's default link location.  If the host
>> default link location is above 2G you may be good; above
>> 4G is even better.
> 
> Well, the output of ld --verbose says:
> 
>   PROVIDE (__executable_start = SEGMENT_START("text-segment",
> 0x400000)); . = SEGMENT_START("text-segment", 0x400000) +
> SIZEOF_HEADERS;
> 
> and objdump of a random aarch64 binary suggests the
> text segment defaults to a vaddr of 0x400000, so I guess
> that means we need to change the start address.
> 
> thanks
> -- PMM
> 

I'm trying to get this to run, in order to be able to test the aarch64 TCG User mode support I have under development.

I wrote an aarch64.ld script based on the sections of other binaries, using a high address (0x0600000000). Before I tried what seemed to be the standard number for non-x86(0x0060000000), with the same results.

The program actually runs (I can qemu-x86-64 --help, for example),
but I get in trouble with the bss, in the sense that I get a sigfault at runtime as soon as the QEMU code tries to initialize the TCG Context (tcg_ctx, residing in bss) with memset, during tcg_context_init():

qemu-x86_64[418]: unhandled level 3 translation fault (11) at 0x602187000, esr 0x92000047
pgd = ffffffc01aef8000
[602187000] *pgd=000000009ae52003, *pmd=000000009aef9003, *pte=0000000000000000

Pid: 418, comm:          qemu-x86_64
CPU: 0    Not tainted  (3.8.0-rc6+ #3)
PC is at 0x7fb7d0b2f0
LR is at 0x6000c0494
pc : [<0000007fb7d0b2f0>] lr : [<00000006000c0494>] pstate: 20000000
sp : 0000007ffffff480
x29: 0000007ffffff480 x28: 0000000000000000 
x27: 0000000000000000 x26: 0000000000000000 
x25: 0000000000000000 x24: 0000000000000000 
x23: 0000000000000000 x22: 0000000000000000 
x21: 00000006000073e8 x20: 0000000000000000 
x19: 0000000000000000 x18: 0000007fffffe250 
x17: 0000007fb7d0b2a8 x16: 000000060011fd70 
x15: 0016fcc9b4000000 x14: 0000000000000008 
x13: 00000003e8000000 x12: 0000000000000000 
x11: 0000000000000000 x10: 0000007fb7c92ba8 
x9 : 0000000600006424 x8 : 0000000000000038 
x7 : 0000000000001569 x6 : 000000000000002b 
x5 : 0000000000000000 x4 : 0000000602132080 
x3 : 0000000602187000 x2 : 0000000000055a60 
x1 : 0000000000000000 x0 : 0000000602132080 

Program received signal SIGSEGV, Segmentation fault.
__GI_memset (dstpp=0x602132080 <tcg_ctx>, c=0, len=350816) at memset.c:56
56                ((op_t *) dstp)[0] = cccc;
(gdb) bt
#0  __GI_memset (dstpp=0x602132080 <tcg_ctx>, c=0, len=350816) at memset.c:56
#1  0x00000006000c0494 in tcg_context_init (s=0x602132080 <tcg_ctx>)
    at /home/claudio/git/qemu-really-new/tcg/tcg.c:236
#2  0x00000006000c6988 in cpu_gen_init ()
    at /home/claudio/git/qemu-really-new/translate-all.c:130
#3  0x00000006000c7194 in tcg_exec_init (tb_size=0)
    at /home/claudio/git/qemu-really-new/translate-all.c:592
#4  0x000000060004b9cc in main (argc=2, argv=0x7ffffffdb8, envp=0x7ffffffdd0)
    at /home/claudio/git/qemu-really-new/linux-user/main.c:3624

----

This is the aarch64.ld script I am using. The problem is probably here,
since I wrote it without fully understanding it.
Can someone save the day?

----

OUTPUT_FORMAT("elf64-littleaarch64", "elf64-littleaarch64", "elf64-littleaarch64");
OUTPUT_ARCH(aarch64)
ENTRY(_start)
SECTIONS
{
  /* Read-only sections, merged into text segment: */
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