[PATCH] Avoid crash with cross-linux core file

[PATCH] Avoid crash with cross-linux core file

[Tom Tromey]

An internal test case creates a core file using gcore, then restarts
gdb with that core.  When run with a cross-linux gdb (in this case,
x86-64 host with ppc64-linux target), the test fails:

    | (gdb) core core
    | [New LWP 18437]
    | warning: `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.
    | warning: Could not load shared library symbols for /lib64/ld64.so.1.
    | Do you need "set solib-search-path" or "set sysroot"?
    | ../../src/gdb/gdbarch.c:3388: internal-error: int gdbarch_elf_make_msymbol_special_p(gdbarch*): Assertion `gdbarch != NULL' failed.
    | A problem internal to GDB has been detected,
    | further debugging may prove unreliable.
    | Quit this debugging session? (y or n) y

What's happening here is that the core file lists some shared
libraries.  These aren't available via the solib search path, and so
gdb finds the local (x86-64) libraries.  This is not ideal, but on the
other hand, it is what was asked for -- while the test does set
solib-search-path, it does not set the sysroot.

But, because gdb isn't configured to handle these libraries, it
crashes.

It seems to me that it's better to avoid the crash by having
solib_bfd_open fail in the case where a library is incompatible.  That
is what this patch does.  Now it looks like:

    | [New LWP 15488]
    | Error while mapping shared library sections:
    | `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.

... and does not crash gdb.

I don't have a good setup for testing this using dejagnu, so I don't
know whether an existing gdb test covers this scenario.
---
 gdb/solib.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/gdb/solib.c b/gdb/solib.c
index 3947c2d1d2e..b2205fd245b 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -511,10 +511,10 @@ solib_bfd_open (const char *pathname)
   /* Check bfd arch.  */
   b = gdbarch_bfd_arch_info (target_gdbarch ());
   if (!b->compatible (b, bfd_get_arch_info (abfd.get ())))
-    warning (_("`%s': Shared library architecture %s is not compatible "
-	       "with target architecture %s."), bfd_get_filename (abfd.get ()),
-	     bfd_get_arch_info (abfd.get ())->printable_name,
-	     b->printable_name);
+    error (_("`%s': Shared library architecture %s is not compatible "
+	     "with target architecture %s."), bfd_get_filename (abfd.get ()),
+	   bfd_get_arch_info (abfd.get ())->printable_name,
+	   b->printable_name);
 
   return abfd;
 }
-- 
2.31.1

Re: [PATCH] Avoid crash with cross-linux core file

[John Baldwin]

On 12/15/21 10:33 AM, Tom Tromey via Gdb-patches wrote:
> An internal test case creates a core file using gcore, then restarts
> gdb with that core.  When run with a cross-linux gdb (in this case,
> x86-64 host with ppc64-linux target), the test fails:
> 
>      | (gdb) core core
>      | [New LWP 18437]
>      | warning: `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.
>      | warning: Could not load shared library symbols for /lib64/ld64.so.1.
>      | Do you need "set solib-search-path" or "set sysroot"?
>      | ../../src/gdb/gdbarch.c:3388: internal-error: int gdbarch_elf_make_msymbol_special_p(gdbarch*): Assertion `gdbarch != NULL' failed.
>      | A problem internal to GDB has been detected,
>      | further debugging may prove unreliable.
>      | Quit this debugging session? (y or n) y
> 
> What's happening here is that the core file lists some shared
> libraries.  These aren't available via the solib search path, and so
> gdb finds the local (x86-64) libraries.  This is not ideal, but on the
> other hand, it is what was asked for -- while the test does set
> solib-search-path, it does not set the sysroot.
> 
> But, because gdb isn't configured to handle these libraries, it
> crashes.
> 
> It seems to me that it's better to avoid the crash by having
> solib_bfd_open fail in the case where a library is incompatible.  That
> is what this patch does.  Now it looks like:
> 
>      | [New LWP 15488]
>      | Error while mapping shared library sections:
>      | `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.

Do you no longer get the warning about setting sysroot, etc.?  If it's possible to keep
those that might be nice, but perhaps that means returning an error and the caller would
have to error out later (or maybe moving the suggestion message earlier to be part of this
error?)  I do think it is true that if the solib isn't compatible, we probably shouldn't
keep trying to use it "just in case".

-- 
John Baldwin

Re: [PATCH] Avoid crash with cross-linux core file

[Tom Tromey]

>>>>> "John" == John Baldwin <jhb@FreeBSD.org> writes:

>> | [New LWP 15488]
>> | Error while mapping shared library sections:
>> | `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.

John> Do you no longer get the warning about setting sysroot, etc.?

I finally got around to reproducing this one so I could answer your
question.  Anyway, the answer is that we do still get it:

    Error while mapping shared library sections:
    `/lib64/libc.so.6': Shared library architecture i386:x86-64 is not compatible with target architecture powerpc:common64.
    warning: Could not load shared library symbols for /lib64/ld64.so.1.
    Do you need "set solib-search-path" or "set sysroot"?

I'm going to check this patch in.

thanks,
Tom

Re: [PATCH] Avoid crash with cross-linux core file

[John Baldwin]

On 3/11/22 8:24 AM, Tom Tromey wrote:
>>>>>> "John" == John Baldwin <jhb@FreeBSD.org> writes:
> 
>>> | [New LWP 15488]
>>> | Error while mapping shared library sections:
>>> | `/lib64/libc.so.6': Shared library architecture unknown is not compatible with target architecture powerpc:common64.
> 
> John> Do you no longer get the warning about setting sysroot, etc.?
> 
> I finally got around to reproducing this one so I could answer your
> question.  Anyway, the answer is that we do still get it:
> 
>      Error while mapping shared library sections:
>      `/lib64/libc.so.6': Shared library architecture i386:x86-64 is not compatible with target architecture powerpc:common64.
>      warning: Could not load shared library symbols for /lib64/ld64.so.1.
>      Do you need "set solib-search-path" or "set sysroot"?
> 
> I'm going to check this patch in.

Ok, thanks for checking.  I didn't mean to be a blocker.

-- 
John Baldwin

Re: [PATCH] Avoid crash with cross-linux core file

[Tom Tromey]

John> Ok, thanks for checking.  I didn't mean to be a blocker.

It's no problem, I felt that was a good question that I hadn't thought
of, and so I wanted to check it before committing.

Tom