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[PATCH 5/5 v4] Allow target to decide where to map jump-pad.
- From: Wei-cheng Wang <cole945 at gmail dot com>
- To: uweigand at de dot ibm dot com, gdb-patches at sourceware dot org
- Cc: Wei-cheng Wang <cole945 at gmail dot com>
- Date: Sun, 28 Jun 2015 00:21:42 +0800
- Subject: [PATCH 5/5 v4] Allow target to decide where to map jump-pad.
- Authentication-results: sourceware.org; auth=none
- References: <1435422102-39438-1-git-send-email-cole945 at gmail dot com>
Ulrich Weigand wrote:
> Looks OK to me. Note that getauxval was only introduced with
> a relatively recent glibc release, so might warrant a configure
> check to avoid breaking the build on older releases ...
Current configure.ac had alreadly check getauxval,
AC_CHECK_FUNCS(getauxval pread pwrite pread64 setns)
so I simply add the old-fashioned-way getauxval fallback if it's not there.
Thanks,
Wei-cheng
---
This patch adds an IPA function, jump_pad_area_hint, for giving a hint
where to map jump pad buffer. For some targets, addr = page-size is
too far to reach from executable.
gdb/gdbserver/ChangeLog
2015-06-27 Wei-cheng Wang <cole945@gmail.com>
* tracepoint.c (initialize_tracepoint): Call jump_pad_area_hint
to get where to map gdb_jump_pad_buffer. Remove MAP_FIXED.
* tracepoint.h (jump_pad_area_hint): Add declaration.
* linux-amd64-ipa.c (jump_pad_area_hint): New function.
* linux-i386-ipa.c (jump_pad_area_hint): New function.
* linux-ppc-ipa.c (jump_pad_area_hint): New function.
(getauxvl): New function.
---
gdb/gdbserver/linux-amd64-ipa.c | 10 ++++++++
gdb/gdbserver/linux-i386-ipa.c | 10 ++++++++
gdb/gdbserver/linux-ppc-ipa.c | 51 +++++++++++++++++++++++++++++++++++++++++
gdb/gdbserver/tracepoint.c | 7 +++---
gdb/gdbserver/tracepoint.h | 3 +++
5 files changed, 77 insertions(+), 4 deletions(-)
diff --git a/gdb/gdbserver/linux-amd64-ipa.c b/gdb/gdbserver/linux-amd64-ipa.c
index a6dfb03..65cd748 100644
--- a/gdb/gdbserver/linux-amd64-ipa.c
+++ b/gdb/gdbserver/linux-amd64-ipa.c
@@ -77,6 +77,16 @@ gdb_agent_get_raw_reg (const unsigned char *raw_regs, int regnum)
return *(ULONGEST *) (raw_regs + x86_64_ft_collect_regmap[regnum]);
}
+/* See tracepoint.h. */
+
+uintptr_t
+jump_pad_area_hint (void)
+{
+ /* Allocate scratch buffer aligned on a page boundary, at a low
+ address (close to the main executable's code). */
+ return sysconf (_SC_PAGE_SIZE);
+}
+
#ifdef HAVE_UST
#include <ust/processor.h>
diff --git a/gdb/gdbserver/linux-i386-ipa.c b/gdb/gdbserver/linux-i386-ipa.c
index eb30dcd..dc0dfaf 100644
--- a/gdb/gdbserver/linux-i386-ipa.c
+++ b/gdb/gdbserver/linux-i386-ipa.c
@@ -114,6 +114,16 @@ gdb_agent_get_raw_reg (const unsigned char *raw_regs, int regnum)
return *(int *) (raw_regs + i386_ft_collect_regmap[regnum]);
}
+/* See tracepoint.h. */
+
+uintptr_t
+jump_pad_area_hint (void)
+{
+ /* Allocate scratch buffer aligned on a page boundary, at a low
+ address (close to the main executable's code). */
+ return sysconf (_SC_PAGE_SIZE);
+}
+
#ifdef HAVE_UST
#include <ust/processor.h>
diff --git a/gdb/gdbserver/linux-ppc-ipa.c b/gdb/gdbserver/linux-ppc-ipa.c
index 73d8899..ddb2174 100644
--- a/gdb/gdbserver/linux-ppc-ipa.c
+++ b/gdb/gdbserver/linux-ppc-ipa.c
@@ -21,6 +21,8 @@
#include "server.h"
#include "tracepoint.h"
+#include <sys/auxv.h>
+
#if defined __PPC64__
void init_registers_powerpc_64l (void);
extern const struct target_desc *tdesc_powerpc_64l;
@@ -105,6 +107,55 @@ gdb_agent_get_raw_reg (const unsigned char *raw_regs, int regnum)
+ ppc_ft_collect_regmap[regnum] * REGSZ);
}
+#ifndef HAVE_GETAUXVAL
+/* Retrieve the value of TYPE from the auxiliary vector. If TYPE is not
+ found, 0 is returned. This function is provided if glibc is too old. */
+
+static unsigned long
+getauxval (unsigned long type)
+{
+ unsigned long data[2];
+ FILE *f = fopen ("/proc/self/auxv", "r");
+ unsigned long value = 0;
+
+ if (f == NULL)
+ return 0;
+
+ while (fread (data, sizeof (data), 1, f) > 0)
+ {
+ if (data[0] == AT_HWCAP)
+ {
+ value = data[1];
+ break;
+ }
+ }
+
+ fclose (f);
+ return value;
+}
+#endif
+
+/* See tracepoint.h. */
+
+uintptr_t
+jump_pad_area_hint (void)
+{
+ /* Use AT_PHDR address to guess where the main executable is mapped,
+ and try to map the jump pad before it. The jump pad should be
+ closed enough to the executable for unconditional branch (+/- 32MB). */
+
+ const int SCRATCH_BUFFER_NPAGES = 20;
+ uintptr_t base = getauxval (AT_PHDR);
+ uintptr_t pagesz = sysconf (_SC_PAGE_SIZE);
+ uintptr_t hint = (base & ~(pagesz - 1)) - SCRATCH_BUFFER_NPAGES * pagesz;
+
+ /* Return the lowest possible value if wrap-around. */
+ if (hint > base)
+ hint = pagesz;
+
+ return hint;
+}
+
/* Initialize ipa_tdesc and others. */
void
diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c
index fdec7db..d1c03cf 100644
--- a/gdb/gdbserver/tracepoint.c
+++ b/gdb/gdbserver/tracepoint.c
@@ -7355,13 +7355,12 @@ initialize_tracepoint (void)
#define SCRATCH_BUFFER_NPAGES 20
- /* Allocate scratch buffer aligned on a page boundary, at a low
- address (close to the main executable's code). */
- for (addr = pagesize; addr != 0; addr += pagesize)
+ addr = jump_pad_area_hint ();
+ for (; addr != 0; addr += pagesize)
{
gdb_jump_pad_buffer = mmap ((void *) addr, pagesize * SCRATCH_BUFFER_NPAGES,
PROT_READ | PROT_WRITE | PROT_EXEC,
- MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
+ MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
if (gdb_jump_pad_buffer != MAP_FAILED)
break;
diff --git a/gdb/gdbserver/tracepoint.h b/gdb/gdbserver/tracepoint.h
index 30d0b58..139894f 100644
--- a/gdb/gdbserver/tracepoint.h
+++ b/gdb/gdbserver/tracepoint.h
@@ -131,6 +131,9 @@ void supply_static_tracepoint_registers (struct regcache *regcache,
CORE_ADDR pc);
void set_trampoline_buffer_space (CORE_ADDR begin, CORE_ADDR end,
char *errmsg);
+/* Return the address for where to allocate buffer for jump pad.
+ The buffer should be close enough for tracepoints. */
+uintptr_t jump_pad_area_hint (void);
extern const struct target_desc *ipa_tdesc;
--
1.9.1