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

[Daniel Jacobowitz <drow@false.org>]

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

-- 
Daniel Jacobowitz
CodeSourcery