Handle __gmon_start__ as undefined weak on hppa.

[BZ libc/19170]
	* sysdeps/hppa/crti.S: Declare PREINIT_FUNCTION weak_extern when
	PREINIT_FUNCTION_WEAK is nonzero.
	(gmon_initializer): New function.  Put procedure label for it in
	.init_array section.
	(_init): Don't call PREINIT_FUNCTION.
	* sysdeps/hppa/crtn.S (__gmon_start__): Remove.
	* sysdeps/hppa/dl-lookupcfg.h (DL_FIXUP_MAKE_VALUE): Create null fixup
	value when map argument is null.

ChangeLog

@@ -1,5 +1,15 @@
 2017-12-02  John David Anglin  <danglin@gcc.gnu.org>
 
+	[BZ libc/19170]
+	* sysdeps/hppa/crti.S: Declare PREINIT_FUNCTION weak_extern when
+	PREINIT_FUNCTION_WEAK is nonzero.
+	(gmon_initializer): New function.  Put procedure label for it in
+	.init_array section.
+	(_init): Don't call PREINIT_FUNCTION.
+	* sysdeps/hppa/crtn.S (__gmon_start__): Remove.
+	* sysdeps/hppa/dl-lookupcfg.h (DL_FIXUP_MAKE_VALUE): Create null fixup
+	value when map argument is null.
+
 	* sysdeps/hppa/dl-fptr.c (elf_machine_resolve): Remove unnecessary
 	depi instruction from PIC pc-relative sequence.
 	* sysdeps/hppa/dl-fptr.h (ELF_MACHINE_LOAD_ADDRESS): Likewise.

sysdeps/hppa/crti.S

@@ -49,6 +49,95 @@
 # define PREINIT_FUNCTION_WEAK 1
 #endif
 
+#if PREINIT_FUNCTION_WEAK
+	weak_extern (PREINIT_FUNCTION)
+#else
+	.hidden PREINIT_FUNCTION
+#endif
+
+
+/* If we have working .init_array support, we want to keep the .init
+   section empty (apart from the mandatory prologue/epilogue.  This
+   ensures that the default unwind conventions (return-pointer in b0,
+   frame state in ar.pfs, etc.)  will do the Right Thing.  To ensure
+   an empty .init section, we register gmon_initializer() via the
+   .init_array.
+
+    --davidm 02/10/29 */
+
+#if PREINIT_FUNCTION_WEAK
+/* This blob of assembly code is one simple C function:
+
+static void
+__attribute__ ((used))
+gmon_initializer (void)
+{
+  extern void weak_function __gmon_start__ (void);
+
+  if (__gmon_start__)
+    (*__gmon_start__)();
+}
+
+In a final executable, PLABEL32 relocations for function pointers are
+resolved at link time.  Typically, binutils/ld resolves __gmon_start__
+using an external shared library.  __gmon_start__ is always called if
+it is found at link time.  If __gmon_start__ is not found at runtime
+due to a library update, then the function pointer will point at a null
+function descriptor and calling it will cause a segmentation fault.
+So, we call __canonicalize_funcptr_for_compare to obtain the canonicalized
+address of __gmon_start__ and skip calling __gmon_start__ if it is zero.
+
+ */
+	.type __canonicalize_funcptr_for_compare,@function
+	.type $$dyncall,@function
+
+	.section .data.rel.ro,"aw",@progbits
+	.align 4
+.LC0:
+	.type __gmon_start__,@function
+	.word P%__gmon_start__
+
+	.text
+	.align 4
+	.type gmon_initializer,@function
+gmon_initializer:
+	.PROC
+	.CALLINFO FRAME=64,CALLS,SAVE_RP,ENTRY_GR=4
+	.ENTRY
+	stw %r2,-20(%r30)
+	stwm %r4,64(%r30)
+	stw %r3,-60(%r30)
+	addil LT'.LC0,%r19
+	ldw RT'.LC0(%r1),%r28
+	ldw 0(%r28),%r3
+	comib,= 0,%r3,1f
+	copy %r19,%r4
+	stw %r19,-32(%r30)
+	bl __canonicalize_funcptr_for_compare,%r2
+	copy %r3,%r26
+	comib,= 0,%r28,1f
+	copy %r4,%r19
+	copy %r3,%r22
+	.CALL ARGW0=GR
+	bl $$dyncall,%r31
+	copy %r31,%r2
+1:
+	ldw -84(%r30),%r2
+	ldw -60(%r30),%r3
+	bv %r0(%r2)
+	ldwm -64(%r30),%r4
+	.EXIT
+	.PROCEND
+	.size gmon_initializer, .-gmon_initializer
+
+# undef PREINIT_FUNCTION
+# define PREINIT_FUNCTION gmon_initializer
+#endif
+
+	.section .init_array, "aw"
+	.word P% PREINIT_FUNCTION
+
+
 /* _init prologue.  */
 	.section .init, "ax", %progbits
 	.align 4
@@ -58,14 +147,6 @@ _init:
 	stw	%rp,-20(%sp)
 	stwm	%r4,64(%sp)
 	stw	%r19,-32(%sp)
-#if PREINIT_FUNCTION_WEAK
-	bl	PREINIT_FUNCTION,%rp
-	copy	%r19,%r4	/* delay slot */
-#else
-	bl	PREINIT_FUNCTION,%rp
-	copy	%r19,%r4	/* delay slot */
-#endif
-	copy	%r4,%r19
 
 /* _fini prologue.  */
         .section .fini,"ax",%progbits

sysdeps/hppa/crtn.S

@@ -38,27 +38,6 @@
 /* crtn.S puts function epilogues in the .init and .fini sections
    corresponding to the prologues in crti.S. */
 
-/* Note that we cannot have a weak undefined __gmon_start__, because
-   that would require this to be PIC, and the linker is currently not
-   able to generate a proper procedure descriptor for _init.  Sad but
-   true.  Anyway, HPPA is one of those horrible architectures where
-   making the comparison and indirect call is quite expensive (see the
-   comment in sysdeps/generic/initfini.c). */
-        .text
-        .align 4
-        .weak   __gmon_start__
-        .type    __gmon_start__,@function
-__gmon_start__:
-	.proc
-	.callinfo
-	.entry
-        bv,n %r0(%r2)
-	.exit
-	.procend
-
-/* Here is the tail end of _init.  We put __gmon_start before this so
-   that the assembler creates the .PARISC.unwind section for us, ie.
-   with the right attributes.  */
 	.section .init, "ax", @progbits
 	ldw	-84(%sp),%rp
 	copy	%r4,%r19

sysdeps/hppa/dl-lookupcfg.h

@@ -73,7 +73,8 @@ void attribute_hidden _dl_unmap (struct link_map *map);
 
 /* Construct a fixup value from the address and linkmap */
 #define DL_FIXUP_MAKE_VALUE(map, addr) \
-   ((struct fdesc) { (addr), (map)->l_info[DT_PLTGOT]->d_un.d_ptr })
+  (map) ? ((struct fdesc) { (addr), (map)->l_info[DT_PLTGOT]->d_un.d_ptr }) \
+	: ((struct fdesc) { 0, 0 })
 
 /* Extract the code address from a fixup value */
 #define DL_FIXUP_VALUE_CODE_ADDR(value) ((value).ip)