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[src/trunk]: src/libexec/ld.elf_so/arch/alpha Fix a serious performance probl...
details: https://anonhg.NetBSD.org/src/rev/a5d00ea729c6
branches: trunk
changeset: 536119:a5d00ea729c6
user: thorpej <thorpej%NetBSD.org@localhost>
date: Sun Sep 08 02:48:28 2002 +0000
description:
Fix a serious performance problem for large programs on the Alpha.
Large programs need multiple GOTs. The lazy binding stub in the PLT
can be reached from any of these GOTs, but the dynamic linker only
has enough information to fix up the first GOT entry. Thus, calls
through the other GOTs went through the time-consuming lazy binding
process on every call.
This fix rewrites the PLT entries themselves to bypass the lazy binding
for those GOT entries that the dynamic linker can't fixup.
Fix from FreeBSD.
Note that now that we patch up the PLT, we need to put back the "imb"
that was removed from the binder exit path.
diffstat:
libexec/ld.elf_so/arch/alpha/alpha_reloc.c | 178 ++++++++++++++++++++++++++++-
libexec/ld.elf_so/arch/alpha/rtld_start.S | 7 +-
2 files changed, 182 insertions(+), 3 deletions(-)
diffs (229 lines):
diff -r ecace7a0dc31 -r a5d00ea729c6 libexec/ld.elf_so/arch/alpha/alpha_reloc.c
--- a/libexec/ld.elf_so/arch/alpha/alpha_reloc.c Sun Sep 08 01:42:55 2002 +0000
+++ b/libexec/ld.elf_so/arch/alpha/alpha_reloc.c Sun Sep 08 02:48:28 2002 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: alpha_reloc.c,v 1.13 2002/09/06 15:17:55 mycroft Exp $ */
+/* $NetBSD: alpha_reloc.c,v 1.14 2002/09/08 02:48:28 thorpej Exp $ */
/*
* Copyright (c) 2001 Wasabi Systems, Inc.
@@ -35,6 +35,31 @@
* POSSIBILITY OF SUCH DAMAGE.
*/
+/*
+ * Copyright 1996, 1997, 1998, 1999 John D. Polstra.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
#include <sys/types.h>
#include <sys/stat.h>
@@ -243,6 +268,7 @@
Elf_Addr new_value;
const Elf_Sym *def;
const Obj_Entry *defobj;
+ Elf_Addr stubaddr;
assert(ELF_R_TYPE(rela->r_info) == R_TYPE(JMP_SLOT));
@@ -253,9 +279,157 @@
new_value = (Elf_Addr)(defobj->relocbase + def->st_value);
rdbg(dodebug, ("bind now/fixup in %s --> old=%p new=%p",
defobj->strtab + def->st_name, (void *)*where, (void *)new_value));
- if (*where != new_value)
+
+ if ((stubaddr = *where) != new_value) {
+ int64_t delta, idisp;
+ uint32_t insn[3], *stubptr;
+ int insncnt;
+ Elf_Addr pc;
+
+ /* Point this GOT entry at the target. */
*where = new_value;
+ /*
+ * Alpha shared objects may have multiple GOTs, each
+ * of which may point to this entry in the PLT. But,
+ * we only have a reference to the first GOT entry which
+ * points to this PLT entry. In order to avoid having to
+ * re-bind this call every time a non-first GOT entry is
+ * used, we will attempt to patch up the PLT entry to
+ * reference the target, rather than the binder.
+ *
+ * When the PLT stub gets control, PV contains the address
+ * of the PLT entry. Each PLT entry has room for 3 insns.
+ * If the displacement of the target from PV fits in a signed
+ * 32-bit integer, we can simply add it to PV. Otherwise,
+ * we must load the GOT entry itself into PV.
+ *
+ * Note if the shared object uses the old PLT format, then
+ * we cannot patch up the PLT safely, and so we skip it
+ * in that case[*].
+ *
+ * [*] Actually, if we're not doing lazy-binding, then
+ * we *can* (and do) patch up this PLT entry; the PLTGOT
+ * thunk won't yet point to any binder entry point, and
+ * so this test will fail as it would for the new PLT
+ * entry format.
+ */
+ if (obj->pltgot[2] == (Elf_Addr) &_rtld_bind_start_old) {
+ rdbg(dodebug, (" old PLT format"));
+ goto out;
+ }
+
+ delta = new_value - stubaddr;
+ rdbg(dodebug, (" stubaddr=%p, where-stubaddr=%ld, delta=%ld",
+ (void *)stubaddr, (long)where - (long)stubaddr,
+ (long)delta));
+ insncnt = 0;
+ if ((int32_t)delta == delta) {
+ /*
+ * We can adjust PV with an LDA, LDAH sequence.
+ *
+ * First, build an LDA insn to adjust the low 16
+ * bits.
+ */
+ insn[insncnt++] = 0x08 << 26 | 27 << 21 | 27 << 16 |
+ (delta & 0xffff);
+ rdbg(dodebug, (" LDA $27,%d($27)", (int16_t)delta));
+ /*
+ * Adjust the delta to account for the effects of
+ * the LDA, including sign-extension.
+ */
+ delta -= (int16_t)delta;
+ if (delta != 0) {
+ /*
+ * Build an LDAH instruction to adjust the
+ * high 16 bits.
+ */
+ insn[insncnt++] = 0x09 << 26 | 27 << 21 |
+ 27 << 16 | ((delta >> 16) & 0xffff);
+ rdbg(dodebug, (" LDAH $27,%d($27)",
+ (int16_t)(delta >> 16)));
+ }
+ } else {
+ int64_t dhigh;
+
+ /* We must load the GOT entry. */
+ delta = (Elf_Addr)where - stubaddr;
+
+ /*
+ * If the GOT entry is too far away from the PLT
+ * entry, then we can't patch up the PLT entry.
+ * This PLT entry will have to be bound for each
+ * GOT entry except for the first one. This program
+ * will still run, albeit very slowly. It is very
+ * unlikely that this case will ever happen in
+ * practice.
+ */
+ if ((int32_t)delta != delta) {
+ rdbg(dodebug,
+ (" PLT stub too far from GOT to relocate"));
+ goto out;
+ }
+ dhigh = delta - (int16_t)delta;
+ if (dhigh != 0) {
+ /*
+ * Build an LDAH instruction to adjust the
+ * high 16 bits.
+ */
+ insn[insncnt++] = 0x09 << 26 | 27 << 21 |
+ 27 << 16 | ((dhigh >> 16) & 0xffff);
+ rdbg(dodebug, (" LDAH $27,%d($27)",
+ (int16_t)(dhigh >> 16)));
+ }
+ /* Build an LDQ to load the GOT entry. */
+ insn[insncnt++] = 0x29 << 26 | 27 << 21 |
+ 27 << 16 | (delta & 0xffff);
+ rdbg(dodebug, (" LDQ $27,%d($27)",
+ (int16_t)delta));
+ }
+
+ /*
+ * Now, build a JMP or BR insn to jump to the target. If
+ * the displacement fits in a sign-extended 21-bit field,
+ * we can use the more efficient BR insn. Otherwise, we
+ * have to jump indirect through PV.
+ */
+ pc = stubaddr + (4 * (insncnt + 1));
+ idisp = (int64_t)(new_value - pc) >> 2;
+ if (-0x100000 <= idisp && idisp < 0x100000) {
+ insn[insncnt++] = 0x30 << 26 | 31 << 21 |
+ (idisp & 0x1fffff);
+ rdbg(dodebug, (" BR $31,%p", (void *)target));
+ } else {
+ insn[insncnt++] = 0x1a << 26 | 31 << 21 |
+ 27 << 16 | (idisp & 0x3fff);
+ rdbg(dodebug, (" JMP $31,($27),%d",
+ (int)(idisp & 0x3fff)));
+ }
+
+ /*
+ * Fill in the tail of the PLT entry first, for reentrancy.
+ * Until we have overwritten the first insn (an unconditional
+ * branch), the remaining insns have no effect.
+ */
+ stubptr = (uint32_t *)stubaddr;
+ while (insncnt > 1) {
+ insncnt--;
+ stubptr[insncnt] = insn[insncnt];
+ }
+ /*
+ * Commit the tail of the insn sequence to memory
+ * before overwriting the first insn.
+ */
+ __asm __volatile("wmb" ::: "memory");
+ stubptr[0] = insn[0];
+ /*
+ * I-stream will be sync'd when we either return from
+ * the binder (lazy bind case) or when the PLTGOT thunk
+ * is patched up (bind-now case).
+ */
+ }
+
+ out:
*addrp = (caddr_t)new_value;
return 0;
}
diff -r ecace7a0dc31 -r a5d00ea729c6 libexec/ld.elf_so/arch/alpha/rtld_start.S
--- a/libexec/ld.elf_so/arch/alpha/rtld_start.S Sun Sep 08 01:42:55 2002 +0000
+++ b/libexec/ld.elf_so/arch/alpha/rtld_start.S Sun Sep 08 02:48:28 2002 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: rtld_start.S,v 1.9 2002/09/04 19:13:01 mycroft Exp $ */
+/* $NetBSD: rtld_start.S,v 1.10 2002/09/08 02:48:28 thorpej Exp $ */
/*
* Copyright 1996 Matt Thomas <matt%3am-software.com@localhost>
@@ -167,6 +167,11 @@
ldq gp, 160(sp) ; \
/* XXX LDGP? */ \
\
+ /* \
+ * We've patched the PLT; sync the I-stream. \
+ */ \
+ imb ; \
+ \
/* Pop the stack frame and turn control to the destination. */ \
lda sp, 168(sp) ; \
jmp zero, (pv)
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