Bug#805730: glibc: __gmon_start__ symbol proliferation on hppa
Source: glibc
Version: 2.19-22
Severity: normal
Tags: patch
Dear Maintainer,
The symbol __gmon_start__ is defined on the hppa in crtn.S. As a result,
there is a weak definition in every executable. This was originally done
to address problems in the handling of weak undefined symbols. However,
the definition breaks the build of harfbuzz and vlc. It breaks the
--as-needed processing of binutils/ld and this results in unnecessary
libraries being needed by executables.
The patch removes this definition and improves the handling of weak
undefined symbols in glibc. The effect of removing __gmon_start is
handled by the dynamic linker, so it not necessary to immediately recompile
everything.
The problem is reported upstream here:
https://sourceware.org/bugzilla/show_bug.cgi?id=19170
Submitted patch is here:
https://sourceware.org/ml/libc-alpha/2015-11/msg00279.html
The attached change was installed in the +b4 build of 2.19-22 and no
regressions have been observed.
Would you please add the change to the debian/hppa patch set for glibc.
Regards,
Dave Anglin
-- System Information:
Debian Release: stretch/sid
APT prefers unreleased
APT policy: (500, 'unreleased'), (500, 'unstable')
Architecture: hppa (parisc64)
Kernel: Linux 3.18.24+ (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) (ignored: LC_ALL set to en_CA.utf8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)
Index: glibc-2.19/ports/sysdeps/hppa/crti.S
===================================================================
--- glibc-2.19.orig/ports/sysdeps/hppa/crti.S
+++ glibc-2.19/ports/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
Index: glibc-2.19/ports/sysdeps/hppa/crtn.S
===================================================================
--- glibc-2.19.orig/ports/sysdeps/hppa/crtn.S
+++ glibc-2.19/ports/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
Index: glibc-2.19/ports/sysdeps/hppa/dl-lookupcfg.h
===================================================================
--- glibc-2.19.orig/ports/sysdeps/hppa/dl-lookupcfg.h
+++ glibc-2.19/ports/sysdeps/hppa/dl-lookupcfg.h
@@ -74,7 +74,9 @@ void _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)
Index: glibc-2.19/ports/sysdeps/hppa/dl-trampoline.S
===================================================================
--- glibc-2.19.orig/ports/sysdeps/hppa/dl-trampoline.S
+++ glibc-2.19/ports/sysdeps/hppa/dl-trampoline.S
@@ -82,6 +82,11 @@ _dl_runtime_resolve:
bl _dl_fixup,%rp
copy %r21,%r19 /* set fixup func ltp */
+ /* Sometimes a final executable may attempt to call an undefined
+ weak function (e.g., __gmon_start__). Return if the function
+ was not resolved by _dl_fixup */
+ comib,= 0,%r28,1f
+
/* Load up the returned func descriptor */
copy %r28, %r22
copy %r29, %r19
@@ -107,6 +112,13 @@ _dl_runtime_resolve:
/* Jump to new function, but return to previous function */
bv %r0(%r22)
ldw -20(%sp),%rp
+
+1:
+ /* Return to previous function */
+ ldw -148(%sp),%rp
+ bv %r0(%rp)
+ ldo -128(%sp),%sp
+
.EXIT
.PROCEND
cfi_endproc
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