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

Josh Poimboeuf
2025-01-22T02:35:20Z

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;
};