Re: [patch] Relocate phdr in read_program_header

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Fri, 30 Sep 2011 21:31:33 +0200, Aleksandar Ristovski wrote:
>     * solib-svr4.c (read_program_header): If PT_PHDR is present, use it
>     to calculate correct address in case of PIE.

FSF ChangeLog should describe the changes, not their reason.  Therefore:
	* solib-svr4.c (read_program_header): New variable pt_phdr, initialize
	it from target PT_PHDR p_vaddr, relocate sect_addr by it.


> --- gdb/solib-svr4.c	30 Aug 2011 02:48:05 -0000	1.154
> +++ gdb/solib-svr4.c	30 Sep 2011 17:47:13 -0000
> @@ -385,7 +385,7 @@ static gdb_byte *
>  read_program_header (int type, int *p_sect_size, int *p_arch_size)
>  {
>    enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch);
> -  CORE_ADDR at_phdr, at_phent, at_phnum;
> +  CORE_ADDR at_phdr, at_phent, at_phnum, pt_phdr;
>    int arch_size, sect_size;
>    CORE_ADDR sect_addr;
>    gdb_byte *buf;
> @@ -408,6 +408,10 @@ read_program_header (int type, int *p_se
>    else
>      return 0;
>  
> +  pt_phdr = (CORE_ADDR)-1; /* Address of the first entry. If not PIE,
> +			      this will be zero.
> +			      For PIE, it will be unrelocated at_phdr. */

There is CORE_ADDR_MAX.  But I would prefer new `int pt_phdr_p' as "predicate"
boolean flag for valid pt_phdr value, these special values are fragile and one
has to think whether they can happen.


> +
>    /* Find the requested segment.  */
>    if (type == -1)
>      {
> @@ -427,6 +431,11 @@ read_program_header (int type, int *p_se
>  	    return 0;
>  
>  	  if (extract_unsigned_integer ((gdb_byte *)phdr.p_type,
> +					4, byte_order) == PT_PHDR)
> +	    pt_phdr = extract_unsigned_integer ((gdb_byte *)phdr.p_vaddr,
> +						4, byte_order);
> +
> +	  if (extract_unsigned_integer ((gdb_byte *)phdr.p_type,
>  					4, byte_order) == type)

That p_type could be decoded only once.  Also any casta are `(type) val' with
a space accoridng to GCS (GNU Coding Standards).


>  	    break;
>  	}
> @@ -453,6 +462,11 @@ read_program_header (int type, int *p_se
>  	    return 0;
>  
>  	  if (extract_unsigned_integer ((gdb_byte *)phdr.p_type,
> +					4, byte_order) == PT_PHDR)
> +	    pt_phdr = extract_unsigned_integer ((gdb_byte *)phdr.p_vaddr,
> +						8, byte_order);
> +
> +	  if (extract_unsigned_integer ((gdb_byte *)phdr.p_type,
>  					4, byte_order) == type)
>  	    break;
>  	}
> @@ -467,6 +481,16 @@ read_program_header (int type, int *p_se
>  					    8, byte_order);
>      }
>  
> +  /* at_phdr is real address in memory. pt_phdr is what pheader says it is.
> +     Relocation offset is the difference between the two. */
> +  if (pt_phdr != (CORE_ADDR)-1)
> +    {
> +      /* PT_PHDR is optional in the execution view, but we really need it
> +	 for PIE to make this work in general.  However, if not found,
> +	 work with what you have.  */
> +      sect_addr = sect_addr + (at_phdr - pt_phdr);
> +    }
> +
>    /* Read in requested program header.  */
>    buf = xmalloc (sect_size);
>    if (target_read_memory (sect_addr, buf, sect_size))


Just about the style, I do not see any problems of the patch, thanks.

Wrote the testcase, it is probably GNU/Linux-specific.

I would like to review yet the changes.


Thanks,
Jan


2011-10-16  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/attach-pie-noexec.c: New files.
	* gdb.base/attach-pie-noexec.exp: New files.

--- /dev/null
+++ b/gdb/testsuite/gdb.base/attach-pie-noexec.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2011 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+
+int
+main (void)
+{
+  sleep (600);
+  return 0;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/attach-pie-noexec.exp
@@ -0,0 +1,66 @@
+# Copyright (C) 2011 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Manipulation with PID on target is not supported.
+if [is_remote target] then {
+    return 0
+}
+
+set testfile attach-pie-noexec
+set executable ${testfile}
+set binfile ${objdir}/${subdir}/${executable}
+
+if { [prepare_for_testing ${testfile}.exp $executable "" [list debug "additional_flags=-fPIE -pie"]] } {
+    return -1
+}
+
+clean_restart $executable
+set arch ""
+set test "show architecture"
+gdb_test_multiple $test $test {
+    -re "The target architecture is set automatically \\(currently (.*)\\)\r\n$gdb_prompt $" {
+	set arch $expect_out(1,string)
+	pass $test
+    }
+}
+if ![runto_main] {
+    return 0
+}
+set test "sanity check info shared"
+gdb_test_multiple "info shared" $test {
+    -re "From\[ \t\]+To\[ \t\]+Syms Read\[ \t\]+Shared Object Library\r\n0x.*\r\n$gdb_prompt $" {
+	pass $test
+    }
+    -re "No shared libraries loaded at this time\\.\r\n$gdb_prompt $" {
+	untested ${testfile}.exp
+    }
+}
+gdb_exit
+
+if {$arch == ""} {
+    untested ${testfile}.exp
+    return 0
+}
+
+set testpid [eval exec $binfile &]
+exec sleep 2
+
+gdb_start
+file delete -- $binfile
+gdb_test "attach $testpid" "Attaching to process $testpid\r\n.*: No such file or directory\\." "attach"
+gdb_test "set architecture $arch" "The target architecture is assumed to be $arch"
+gdb_test "info shared" "From\[ \t\]+To\[ \t\]+Syms Read\[ \t\]+Shared Object Library\r\n0x.*"
+
+eval exec kill -9 $testpid