[PATCH] static-PIE: Update DT_DEBUG for debugger [BZ #23206]

[PATCH] static-PIE: Update DT_DEBUG for debugger [BZ #23206]

[H.J. Lu]

This is needed to support debugging dlopened shared libraries in static
PIE.

OK for master?

H.J.
	[BZ #23206]
	* elf/dl-reloc-static-pie.c (_dl_relocate_static_pie): Initialize
	_r_debug and update DT_DEBUG for debugger.
---
 elf/dl-reloc-static-pie.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
index bd2d516e5d..ab1ce0eacc 100644
--- a/elf/dl-reloc-static-pie.c
+++ b/elf/dl-reloc-static-pie.c
@@ -48,5 +48,21 @@ _dl_relocate_static_pie (void)
      data access using the global offset table.  */
   ELF_DYNAMIC_RELOCATE (main_map, 0, 0, 0);
   main_map->l_relocated = 1;
+
+  /* Initialize _r_debug.  */
+  struct r_debug *r = _dl_debug_initialize (0, LM_ID_BASE);
+  r->r_state = RT_CONSISTENT;
+
+  /* Set up debugging before the debugger is notified for the first
+     time.  */
+# ifdef ELF_MACHINE_DEBUG_SETUP
+  /* Some machines (e.g. MIPS) don't use DT_DEBUG in this way.  */
+  ELF_MACHINE_DEBUG_SETUP (main_map, r);
+# else
+  if (main_map->l_info[DT_DEBUG] != NULL)
+    /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
+       with the run-time address of the r_debug structure  */
+    main_map->l_info[DT_DEBUG]->d_un.d_ptr = (ElfW(Addr)) r;
+# endif
 }
 #endif
-- 
2.17.0

Re: [PATCH] static-PIE: Update DT_DEBUG for debugger [BZ #23206]

[Carlos O'Donell]

On 05/29/2018 08:08 AM, H.J. Lu wrote:
> This is needed to support debugging dlopened shared libraries in static
> PIE.
> 
> OK for master?
> 

This looks good. We always need to setup r_debug properly and this looks
like the right solution to me. IIUC we set RT_CONSISTENT at this point because
we are consistent (not doing anything with the link map the debugger needs to
be aware of).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> H.J.
> 	[BZ #23206]
> 	* elf/dl-reloc-static-pie.c (_dl_relocate_static_pie): Initialize
> 	_r_debug and update DT_DEBUG for debugger.
> ---
>  elf/dl-reloc-static-pie.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
> index bd2d516e5d..ab1ce0eacc 100644
> --- a/elf/dl-reloc-static-pie.c
> +++ b/elf/dl-reloc-static-pie.c
> @@ -48,5 +48,21 @@ _dl_relocate_static_pie (void)
>       data access using the global offset table.  */
>    ELF_DYNAMIC_RELOCATE (main_map, 0, 0, 0);
>    main_map->l_relocated = 1;
> +
> +  /* Initialize _r_debug.  */
> +  struct r_debug *r = _dl_debug_initialize (0, LM_ID_BASE);
> +  r->r_state = RT_CONSISTENT;
> +
> +  /* Set up debugging before the debugger is notified for the first
> +     time.  */
> +# ifdef ELF_MACHINE_DEBUG_SETUP
> +  /* Some machines (e.g. MIPS) don't use DT_DEBUG in this way.  */
> +  ELF_MACHINE_DEBUG_SETUP (main_map, r);
> +# else
> +  if (main_map->l_info[DT_DEBUG] != NULL)
> +    /* There is a DT_DEBUG entry in the dynamic section.  Fill it in
> +       with the run-time address of the r_debug structure  */
> +    main_map->l_info[DT_DEBUG]->d_un.d_ptr = (ElfW(Addr)) r;
> +# endif
>  }
>  #endif
>