Re: [PATCH v4 00/39] unwind, perf: sframe user space unwinding

[Josh Poimboeuf <jpoimboe@kernel.org>]

On Tue, Jan 21, 2025 at 06:30:52PM -0800, Josh Poimboeuf wrote:
> For testing with user space, here are the latest binutils fixes:
> 
>   1785837a2570 ("ld: fix PR/32297")
>   938fb512184d ("ld: fix wrong SFrame info for lazy IBT PLT")
>   47c88752f9ad ("ld: generate SFrame stack trace info for .plt.got")
> 
> An out-of-tree glibc patch is also needed -- will attach in a reply.

Latest out-of-tree glibc patch below:

diff --git a/elf/dl-load.c b/elf/dl-load.c
index e986d7faab..5a593c2126 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -29,6 +29,7 @@
 #include <bits/wordsize.h>
 #include <sys/mman.h>
 #include <sys/param.h>
+#include <sys/prctl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <gnu/lib-names.h>
@@ -87,6 +88,9 @@ struct filebuf
 
 #define STRING(x) __STRING (x)
 
+#ifndef PT_GNU_SFRAME
+#define PT_GNU_SFRAME 0x6474e554
+#endif
 
 /* This is the decomposed LD_LIBRARY_PATH search path.  */
 struct r_search_path_struct __rtld_env_path_list attribute_relro;
@@ -1186,6 +1190,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	  l->l_relro_addr = ph->p_vaddr;
 	  l->l_relro_size = ph->p_memsz;
 	  break;
+
+	case PT_GNU_SFRAME:
+	  l->l_sframe_start = ph->p_vaddr;
+	  l->l_sframe_end   = ph->p_vaddr + ph->p_memsz;
+	  break;
 	}
 
     if (__glibc_unlikely (nloadcmds == 0))
@@ -1236,6 +1245,26 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	l->l_map_start = l->l_map_end = 0;
 	goto lose;
       }
+
+#define PR_ADD_SFRAME 77
+    if (l->l_sframe_start != 0)
+    {
+      l->l_sframe_start += l->l_addr;
+      l->l_sframe_end   += l->l_addr;
+
+      for (size_t i = 0; i < nloadcmds; i++)
+      {
+	struct loadcmd *c = &loadcmds[i];
+
+	if (c->prot & PROT_EXEC)
+	{
+	  ElfW(Addr) text_start = l->l_addr + c->mapstart;
+	  ElfW(Addr) text_end   = l->l_addr + c->mapend;
+
+	  __prctl(PR_ADD_SFRAME, l->l_sframe_start, l->l_sframe_end, text_start, text_end);
+	}
+      }
+    }
   }
 
   if (l->l_ld != NULL)
diff --git a/elf/dl-unmap-segments.h b/elf/dl-unmap-segments.h
index f16f4d7ded..dd14162e00 100644
--- a/elf/dl-unmap-segments.h
+++ b/elf/dl-unmap-segments.h
@@ -21,14 +21,20 @@
 
 #include <link.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 
 /* _dl_map_segments ensures that any whole pages in gaps between segments
    are filled in with PROT_NONE mappings.  So we can just unmap the whole
    range in one fell swoop.  */
 
+#define PR_REMOVE_SFRAME 78
+
 static __always_inline void
 _dl_unmap_segments (struct link_map *l)
 {
+  if (l->l_sframe_start != 0)
+    __prctl(PR_REMOVE_SFRAME, l->l_sframe_start, NULL, NULL, NULL);
+
   __munmap ((void *) l->l_map_start, l->l_map_end - l->l_map_start);
 }
 
diff --git a/elf/setup-vdso.h b/elf/setup-vdso.h
index 888e1e4897..2a6bb9b944 100644
--- a/elf/setup-vdso.h
+++ b/elf/setup-vdso.h
@@ -16,6 +16,11 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include <sys/prctl.h>
+#ifndef PT_GNU_SFRAME
+#define PT_GNU_SFRAME 0x6474e554
+#endif
+
 static inline void __attribute__ ((always_inline))
 setup_vdso (struct link_map *main_map __attribute__ ((unused)),
 	    struct link_map ***first_preload __attribute__ ((unused)))
@@ -52,6 +57,14 @@ setup_vdso (struct link_map *main_map __attribute__ ((unused)),
 	      if (ph->p_vaddr + ph->p_memsz >= l->l_map_end)
 		l->l_map_end = ph->p_vaddr + ph->p_memsz;
 	    }
+	  else if (ph->p_type == PT_GNU_SFRAME)
+	    {
+	      if (! l->l_sframe_start)
+		{
+		  l->l_sframe_start = ph->p_vaddr;
+		  l->l_sframe_end   = ph->p_vaddr + ph->p_memsz;
+		}
+	    }
 	  else
 	    /* There must be no TLS segment.  */
 	    assert (ph->p_type != PT_TLS);
@@ -74,6 +87,15 @@ setup_vdso (struct link_map *main_map __attribute__ ((unused)),
       l->l_local_scope[0]->r_nlist = 1;
       l->l_local_scope[0]->r_list = &l->l_real;
 
+#define PR_ADD_SFRAME 77
+      if (l->l_sframe_start != 0)
+	{
+	  l->l_sframe_start += l->l_addr;
+	  l->l_sframe_end   += l->l_addr;
+
+	  __prctl(PR_ADD_SFRAME, l->l_sframe_start, l->l_sframe_end, l->l_addr, l->l_map_end);
+	}
+
       /* Now that we have the info handy, use the DSO image's soname
 	 so this object can be looked up by name.  */
       if (l->l_info[DT_SONAME] != NULL)
diff --git a/include/link.h b/include/link.h
index 5ed445d5a6..e94390b29e 100644
--- a/include/link.h
+++ b/include/link.h
@@ -345,6 +345,9 @@ struct link_map
     ElfW(Addr) l_relro_addr;
     size_t l_relro_size;
 
+    ElfW(Addr) l_sframe_start;
+    ElfW(Addr) l_sframe_end;
+
     unsigned long long int l_serial;
   };