[PATCH] x86: Properly handle IFUNC function pointer reference

[H.J. Lu]

Update

commit 68c4956b1401de70173848a6bdf620cb42fa9358
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Apr 26 09:08:54 2022 -0700

    x86: Properly handle function pointer reference

to properly handle IFUNC function pointer reference.  Since IFUNC symbol
value is only known at run-time, set pointer_equality_needed for IFUNC
function pointer reference in PDE so that it will be resolved to its PLT
entry directly.

bfd/

	PR ld/29216
	* elf32-i386.c (elf_i386_scan_relocs): Set pointer_equality_needed
	for IFUNC function pointer reference in PDE.
	* elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.

ld/

	PR ld/29216
	* testsuite/ld-ifunc/ifunc.exp: Run PR ld/29216 test.
	* testsuite/ld-ifunc/pr29216.c: New file.
---
 bfd/elf32-i386.c                |  8 ++++-
 bfd/elf64-x86-64.c              |  8 ++++-
 ld/testsuite/ld-ifunc/ifunc.exp |  9 +++++
 ld/testsuite/ld-ifunc/pr29216.c | 62 +++++++++++++++++++++++++++++++++
 4 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 ld/testsuite/ld-ifunc/pr29216.c

diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index b034154fb97..3bc710096aa 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -1778,7 +1778,13 @@ elf_i386_scan_relocs (bfd *abfd,
 		  if (r_type == R_386_32
 		      && (sec->flags & SEC_READONLY) == 0)
 		    func_pointer_ref = true;
-		  else
+
+		  /* IFUNC symbol needs pointer equality in PDE so that
+		     function pointer reference will be resolved to its
+		     PLT entry directly.  */
+		  if (!func_pointer_ref
+		      || (bfd_link_pde (info)
+			  && h->type == STT_GNU_IFUNC))
 		    h->pointer_equality_needed = 1;
 		}
 
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 6d69d6141ee..eac5e83d7f1 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -2221,7 +2221,13 @@ elf_x86_64_scan_relocs (bfd *abfd, struct bfd_link_info *info,
 			      && (r_type == R_X86_64_32
 				  || r_type == R_X86_64_32S))))
 		    func_pointer_ref = true;
-		  else
+
+		  /* IFUNC symbol needs pointer equality in PDE so that
+		     function pointer reference will be resolved to its
+		     PLT entry directly.  */
+		  if (!func_pointer_ref
+		      || (bfd_link_pde (info)
+			  && h->type == STT_GNU_IFUNC))
 		    h->pointer_equality_needed = 1;
 		}
 
diff --git a/ld/testsuite/ld-ifunc/ifunc.exp b/ld/testsuite/ld-ifunc/ifunc.exp
index 1cd8d388b26..fdb65d01f9f 100644
--- a/ld/testsuite/ld-ifunc/ifunc.exp
+++ b/ld/testsuite/ld-ifunc/ifunc.exp
@@ -714,6 +714,15 @@ run_ld_link_exec_tests [list \
 	"pr18841cn" \
 	"pr18841.out" \
     ] \
+    [list \
+	"Run pr29216" \
+	"$NOPIE_LDFLAGS" \
+	"" \
+	{ pr29216.c } \
+	"pr29216" \
+	"pass.out" \
+	"-fPIC" \
+    ] \
 ]
 
 # The pr23169 testcase is not valid.  In general, you can't call ifunc
diff --git a/ld/testsuite/ld-ifunc/pr29216.c b/ld/testsuite/ld-ifunc/pr29216.c
new file mode 100644
index 00000000000..5019c723c2b
--- /dev/null
+++ b/ld/testsuite/ld-ifunc/pr29216.c
@@ -0,0 +1,62 @@
+#include <stdio.h>
+
+static int
+one (void)
+{
+  return -30;
+}
+
+int foo (void) __attribute__ ((ifunc ("resolve_foo")));
+
+void *
+resolve_foo (void)
+{
+  return (void *) one;
+}
+
+typedef int (*foo_p) (void);
+
+foo_p foo_ptr = foo;
+
+foo_p
+__attribute__ ((noinline))
+get_foo_p (void)
+{
+  return foo_ptr;
+}
+
+foo_p
+__attribute__ ((noinline))
+get_foo (void)
+{
+  return foo;
+}
+
+int
+main (void)
+{
+  foo_p p;
+
+  p = get_foo ();
+  if (p != foo)
+    __builtin_abort ();
+  if ((*p) () != -30)
+    __builtin_abort ();
+
+  p = get_foo_p ();
+  if (p != foo)
+    __builtin_abort ();
+  if ((*p) () != -30)
+    __builtin_abort ();
+
+  if (foo_ptr != foo)
+    __builtin_abort ();
+  if ((*foo_ptr) () != -30)
+    __builtin_abort ();
+  if (foo () != -30)
+    __builtin_abort ();
+
+  printf ("PASS\n");
+
+  return 0;
+}
-- 
2.36.1