Re: Failed to read a valid object file image from memory (gdb_6_6-branch, kernel 2.6.20-rc6)

[Neo <cjia@cse.unl.edu>]

Daniel Jacobowitz wrote:
> On Sat, Jan 27, 2007 at 07:22:13PM -0600, Neo wrote:
>   
>> On my machine the configure script assumes that I was equipped with 
>> pread64. But I got an EIO from that system call. Then, I disable the 
>> "HAS_PREAD64" macro, I got an invalid argument error from the read 
>> system call. (in file linux-nat.c)
>>
>> Now, I am curious about the potential fix for this problem.
>>
>> 1) Regardless the HAS_PREAD64 macro, it seems that it will definitely 
>> fail on 32bit machine without large offset support due to that large 
>> offset as 0xFFFE0000.
>> 2) For those machines probably configured with pread64, it seems that 
>> the function does not working well. At least the checking in the 
>> ./gdb/configure is not that strict.
>>     
>
> No - these shouldn't matter.  Glibc is supposed to support pread64 even
> if the syscall is missing.  We're just making sure the system library
> has compile time support for pread64; runtime support is its
> responsibility.  See __emulate_pread64 in glibc.
>
>   
>> 3) Can we just drop the AT_SYSINFO_EHDR that we found in function 
>> add_vsyscall_page?
>>     
>
> I suspect it's actually a kernel bug that you can't read the vsyscall
> page.  You should be able to; for instance, I can using 32-bit
> emulation on a 64-bit system.  
So, what is the kernel version on your emulator?

Thanks,
Neo
> Unfortunately, I don't have a 32-bit
> kernel running anywhere I can test.
>
>   


-- 
I would remember that if researchers were not ambitious
probably today we haven't the technology we are using!