diff mbox series

[v2,1/5] elf: Add SFrame support to _dl_find_object function

Message ID 20250411113456.15213-2-claudiu.zissulescu-ianculescu@oracle.com (mailing list archive)
State Failed CI
Headers
Series glibc: Add SFrame support for stack backtracing |

Checks

Context Check Description
redhat-pt-bot/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Claudiu Zissulescu-Ianculescu April 11, 2025, 11:34 a.m. UTC 
  From: Claudiu Zissulescu <claudiu.zissulescu-ianculescu@oracle.com>

The SFrame provides information to be able to do stack trace is now
well defined and implemented in Binutils 2.41.  The format simply
contains enough information to be able to do stack trace given a
program counter (PC) value, the stack pointer, and the frame pointer.
The SFrame information is stored in a .sframe ELF section, which is
loaded into its own PT_GNU_SFRAME segment. We consider for this support
SFrame version 2.

This patch adds the bits to _dl_find_object to recognize and store in
struct dl_find_object the necessary info about SFrame section.

Signed-off-by: Claudiu Zissulescu <claudiu.zissulescu-ianculescu@oracle.com>
---
 bits/dl_find_object.h |  3 +++
 dlfcn/dlfcn.h         |  7 ++++++-
 elf/dl-find_object.h  | 44 ++++++++++++++++++++++++++++++++++---------
 manual/dynlink.texi   | 25 +++++++++++++++++++++++-
 4 files changed, 68 insertions(+), 11 deletions(-)
diff mbox series

Patch

diff --git a/bits/dl_find_object.h b/bits/dl_find_object.h
index b9f796dc2b..908feece08 100644
--- a/bits/dl_find_object.h
+++ b/bits/dl_find_object.h
@@ -30,3 +30,6 @@ 
 
 /* The ELF segment which contains the exception handling data.  */
 #define DLFO_EH_SEGMENT_TYPE PT_GNU_EH_FRAME
+
+/* The ELF segment which contains the SFrame data.  */
+#define DLFO_SFRAME_SEGMENT_TYPE PT_GNU_SFRAME
diff --git a/dlfcn/dlfcn.h b/dlfcn/dlfcn.h
index 5747962611..411b401c9e 100644
--- a/dlfcn/dlfcn.h
+++ b/dlfcn/dlfcn.h
@@ -217,7 +217,11 @@  struct dl_find_object
   int dlfo_eh_count;		/* Number of exception handling entries.  */
   unsigned int __dlfo_eh_count_pad;
 # endif
-  __extension__ unsigned long long int __dflo_reserved[7];
+  void *dlfo_sframe;		/* SFrame stack trace data of the object.  */
+#if __WORDSIZE == 32
+  unsigned int __dlfo_sframe_pad;
+#endif
+  __extension__ unsigned long long int __dflo_reserved[6];
 };
 
 /* If ADDRESS is found in an object, fill in *RESULT and return 0.
@@ -226,6 +230,7 @@  int _dl_find_object (void *__address, struct dl_find_object *__result) __THROW;
 
 #endif /* __USE_GNU */
 
+#define DLF_SFRAME      (1 << 0)   /* SFrame stack trace data is valid.  */
 
 __END_DECLS
 
diff --git a/elf/dl-find_object.h b/elf/dl-find_object.h
index 0915065be0..54092f9af7 100644
--- a/elf/dl-find_object.h
+++ b/elf/dl-find_object.h
@@ -33,6 +33,7 @@ 
    transactions).  */
 struct dl_find_object_internal
 {
+  unsigned long long int flags;
   uintptr_t map_start;
   uintptr_t map_end;            /* Set to map_start by dlclose.  */
   struct link_map *map;         /* Set to NULL by dlclose.  */
@@ -43,6 +44,7 @@  struct dl_find_object_internal
 #if DLFO_STRUCT_HAS_EH_COUNT
   int eh_count;
 #endif
+  void *sframe;
 };
 
 /* Create a copy of *SOURCE in *COPY using relaxed MO loads and
@@ -51,6 +53,8 @@  static inline void
 _dl_find_object_internal_copy (const struct dl_find_object_internal *source,
                                struct dl_find_object_internal *copy)
 {
+  atomic_store_relaxed (&copy->flags,
+                        atomic_load_relaxed (&source->flags));
   atomic_store_relaxed (&copy->map_start,
                         atomic_load_relaxed (&source->map_start));
   atomic_store_relaxed (&copy->map_end,
@@ -67,13 +71,15 @@  _dl_find_object_internal_copy (const struct dl_find_object_internal *source,
   atomic_store_relaxed (&copy->eh_count,
                         atomic_load_relaxed (&source->eh_count));
 #endif
+  atomic_store_relaxed (&copy->sframe,
+                        atomic_load_relaxed (&source->sframe));
 }
 
 static inline void
 _dl_find_object_to_external (struct dl_find_object_internal *internal,
                              struct dl_find_object *external)
 {
-  external->dlfo_flags = 0;
+  external->dlfo_flags = internal->flags;
   external->dlfo_map_start = (void *) internal->map_start;
   external->dlfo_map_end = (void *) internal->map_end;
   external->dlfo_link_map = internal->map;
@@ -84,6 +90,7 @@  _dl_find_object_to_external (struct dl_find_object_internal *internal,
 # if DLFO_STRUCT_HAS_EH_COUNT
   external->dlfo_eh_count = internal->eh_count;
 # endif
+  external->dlfo_sframe = internal->sframe;
 }
 
 /* Extract the object location data from a link map and writes it to
@@ -92,6 +99,8 @@  static void __attribute__ ((unused))
 _dl_find_object_from_map (struct link_map *l,
                           struct dl_find_object_internal *result)
 {
+  uint64_t read_seg = 0;
+  atomic_store_relaxed (&result->flags, 0);
   atomic_store_relaxed (&result->map_start, (uintptr_t) l->l_map_start);
   atomic_store_relaxed (&result->map_end, (uintptr_t) l->l_map_end);
   atomic_store_relaxed (&result->map, l);
@@ -100,23 +109,40 @@  _dl_find_object_from_map (struct link_map *l,
   atomic_store_relaxed (&result->eh_dbase, (void *) l->l_info[DT_PLTGOT]);
 #endif
 
+  /* Initialize object's exception handling segment and SFrame segment
+     data.  */
+  atomic_store_relaxed (&result->sframe, NULL);
+  atomic_store_relaxed (&result->eh_frame, NULL);
+#if DLFO_STRUCT_HAS_EH_COUNT
+  atomic_store_relaxed (&result->eh_count, 0);
+#endif
+
   for (const ElfW(Phdr) *ph = l->l_phdr, *ph_end = l->l_phdr + l->l_phnum;
        ph < ph_end; ++ph)
-    if (ph->p_type == DLFO_EH_SEGMENT_TYPE)
+    switch (ph->p_type)
       {
+      case DLFO_EH_SEGMENT_TYPE:
         atomic_store_relaxed (&result->eh_frame,
                               (void *) (ph->p_vaddr + l->l_addr));
 #if DLFO_STRUCT_HAS_EH_COUNT
         atomic_store_relaxed (&result->eh_count, ph->p_memsz / 8);
 #endif
-        return;
-      }
+        read_seg |= 1;
+        break;
 
-  /* Object has no exception handling segment.  */
-  atomic_store_relaxed (&result->eh_frame, NULL);
-#if DLFO_STRUCT_HAS_EH_COUNT
-  atomic_store_relaxed (&result->eh_count, 0);
-#endif
+      case DLFO_SFRAME_SEGMENT_TYPE:
+        atomic_store_relaxed (&result->sframe,
+                              (void *) (ph->p_vaddr + l->l_addr));
+        atomic_store_relaxed (&result->flags,
+			      atomic_load_relaxed (&result->flags)
+			      | DLF_SFRAME);
+        read_seg |= 2;
+        /* Fall through.  */
+      default:
+        if (read_seg == 3)
+          return;
+        break;
+      }
 }
 
 /* Called by the dynamic linker to set up the data structures for the
diff --git a/manual/dynlink.texi b/manual/dynlink.texi
index 1500a53de6..865a8dcdf7 100644
--- a/manual/dynlink.texi
+++ b/manual/dynlink.texi
@@ -442,7 +442,7 @@  result data to the caller.
 
 @table @code
 @item unsigned long long int dlfo_flags
-Currently unused and always 0.
+Bit zero signals if SFrame stack data is valid.
 
 @item void *dlfo_map_start
 The start address of the inspected mapping.  This information comes from
@@ -459,6 +459,10 @@  This member contains a pointer to the link map of the object.
 This member contains a pointer to the exception handling data of the
 object.  See @code{DLFO_EH_SEGMENT_TYPE} below.
 
+@item void *dlfo_sframe
+This member contains a pointer to the SFrame stack trace data of the
+object.  See @code{DLFO_SFRAME_SEGMENT_TYPE} below.
+
 @end table
 
 This structure is a GNU extension.
@@ -496,6 +500,25 @@  macro expands to the program header type for the unwinding data.
 This macro is a GNU extension.
 @end deftypevr
 
+@deftypevr Macro int DLFO_SFRAME_SEGMENT_TYPE
+@standards{GNU, dlfcn.h}
+On targets using SFrame stack tracer, this macro expands to
+@code{PT_GNU_SFRAME}.  This indicates that @code{dlfo_sframe} in
+@code{struct dl_find_object} points to the @code{PT_GNU_SFRAME}
+segment of the object.
+
+This macro is a GNU extension.
+@end deftypevr
+
+@deftypevr Macro int DLFO_STRUCT_HAS_SFRAME
+@standards{GNU, dlfcn.h}
+On most targets, this macro is defined as @code{0}.  If it is defined to
+@code{1}, @code{struct dl_find_object} contains an additional member
+@code{dlfo_sframe}.
+
+This macro is a GNU extension.
+@end deftypevr
+
 @deftypefun {int} _dl_find_object (void *@var{address}, struct dl_find_object *@var{result})
 @standards{GNU, dlfcn.h}
 @safety{@mtsafe{}@assafe{}@acsafe{}}