Re: [Libunwind-devel] Error compiling libunwind 1.0.1 in a linux/ia64

[Ken Werner]

On 09/23/2011 08:03 PM, Arun Sharma wrote:
> On Mon, Sep 19, 2011 at 5:59 AM, Harald Servat<address@hidden>  wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Hello,
> >
> > I was compiling libunwind 1.0.1 in a linux/ia64 machine when I found the
> > following error:
> >
> > gcc -DHAVE_CONFIG_H -I. -I../include  -I../include
> > - -I../include/tdep-ia64 -I. -D_GNU_SOURCE -DNDEBUG  -g -O2 -fexceptions
> > - -Wall -Wsign-compare -MT ptrace/_UPT_find_proc_info.o -MD -MP -MF
> > $depbase.Tpo -c -o ptrace/_UPT_find_proc_info.o
> > ptrace/_UPT_find_proc_info.c&&\
> > mv -f $depbase.Tpo $depbase.Po
> > ptrace/_UPT_find_proc_info.c:102: error: conflicting types for
> > ‘_UPTi_find_unwind_table’
> > ptrace/_UPT_internal.h:72: error: previous declaration of
> > ‘_UPTi_find_unwind_table’ was here
> > make[2]: *** [ptrace/_UPT_find_proc_info.o] Error 1
>
> This came from commit b317cb48296ca3837b403782c317f6214a54a7fa.
> I'll fix this one up. Ken: let me know if there is a good reason to
> change the return type to int.

Whoops, I'm sorry. I didn't intend to break any other platforms.

The original _UPTi_find_unwind_table code returned a pointer to 
ui->di_cache which is redundant since ui pointer is an argument of this 
function. However, the unfortunate thing about returning a pointer of 
ui->di_cache is that it indicates only one unw_dyn_info_t can be 
retrieved which is not true in case there are multiple ways to unwind 
(e.g. DWARF and platform specific unwind tables). The local unwinding 
deals with this issue by returning only an int that indicates whether 
the operation was successful or not (see: 
dwarf/Gfind_proc_info-lsb.c:dwarf_callback()) and store  multiple 
unw_dyn_info_t (see: cb_data->di_debug, cb_data->di) in a structure that 
gets passed as an argument. In case of remote unwinding I changed the 
return to int to be as close as possible to what works for local 
unwinding. Unfortunately I forgot about the IA64 code path and didn't 
notice that ptrace/_UPT_get_dyn_info_list_addr.c:get_list_addr() calls 
_UPTi_find_unwind_table to obtain the unw_dyn_info_t.

Commit 962366dace4fed902ad5e89df1b34c13c3224b8b changes the return type 
to unw_dyn_info_t* but doesn't change the code that assumes the return 
type is an integer. In addition to the return type this commit 
accidentally changed the name of the function (a missing underscore). 
Therefore there is no declaration for the functions defined in 
src/ptrace/_UPT_find_proc_info.c for the compiler to check against. This 
hides the fact that the _UPTi_find_unwind_table function for non IA64 
targets still returns an integer.

Regards
Ken