rtld: Clean up PT_NOTE and add PT_GNU_PROPERTY handling

Add generic code to handle PT_GNU_PROPERTY notes. Invalid
content is ignored, _dl_process_pt_gnu_property is always called
after PT_LOAD segments are mapped and it has no failure modes.
Currently only one NT_GNU_PROPERTY_TYPE_0 note is handled, which
contains target specific properties: the _dl_process_gnu_property
hook is called for each property.

The old _dl_process_pt_note and _rtld_process_pt_note differ in how
the program header is read.  The old _dl_process_pt_note is called
before PT_LOAD segments are mapped and _rtld_process_pt_note is called
after PT_LOAD segments are mapped. The old _rtld_process_pt_note is
removed and _dl_process_pt_note is always called after PT_LOAD
segments are mapped and now it has no failure modes.

The program headers are scanned backwards so that PT_NOTE can be
skipped if PT_GNU_PROPERTY exists.

Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

2 files changed, 15 insertions, 12 deletions

diff --git a/sysdeps/generic/dl-prop.h b/sysdeps/generic/dl-prop.h
index 6b0f2aa95a..f1cf576fe3 100644
--- a/sysdeps/generic/dl-prop.h
+++ b/sysdeps/generic/dl-prop.h
@@ -20,11 +20,11 @@
 #define _DL_PROP_H
 
 /* The following functions are used by the dynamic loader and the
-   dlopen machinery to process PT_NOTE entries in the binary or
-   shared object.  The notes can be used to change the behaviour of
-   the loader, and as such offer a flexible mechanism for hooking in
-   various checks related to ABI tags or implementing "flag day" ABI
-   transitions.  */
+   dlopen machinery to process PT_NOTE and PT_GNU_PROPERTY entries in
+   the binary or shared object.  The notes can be used to change the
+   behaviour of the loader, and as such offer a flexible mechanism
+   for hooking in various checks related to ABI tags or implementing
+   "flag day" ABI transitions.  */
 
 static inline void __attribute__ ((always_inline))
 _rtld_main_check (struct link_map *m, const char *program)
@@ -36,17 +36,16 @@ _dl_open_check (struct link_map *m)
 {
 }
 
-#ifdef FILEBUF_SIZE
-static inline int __attribute__ ((always_inline))
-_dl_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph,
-		     int fd, struct filebuf *fbp)
+static inline void __attribute__ ((always_inline))
+_dl_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph)
 {
-  return 0;
 }
-#endif
 
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of L,
+   processing of the properties continues until this returns 0.  */
 static inline int __attribute__ ((always_inline))
-_rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph)
+_dl_process_gnu_property (struct link_map *l, uint32_t type, uint32_t datasz,
+			  void *data)
 {
   return 0;
 }
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index d08b97a5ef..c525ffa12c 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -910,6 +910,10 @@ extern void _dl_setup_hash (struct link_map *map) attribute_hidden;
 extern void _dl_rtld_di_serinfo (struct link_map *loader,
 				 Dl_serinfo *si, bool counting);
 
+/* Process PT_GNU_PROPERTY program header PH in module L after
+   PT_LOAD segments are mapped.  */
+void _dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph);
+
 
 /* Search loaded objects' symbol tables for a definition of the symbol
    referred to by UNDEF.  *SYM is the symbol table entry containing the