[binutils-gdb] Fix breakpoints on file reloads for PIE binaries

[binutils-gdb] Fix breakpoints on file reloads for PIE binaries

[Alan Hayward]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ea142fbfc9c1708a83d3532257d6728e1f5c142e

commit ea142fbfc9c1708a83d3532257d6728e1f5c142e
Author: Alan Hayward <alan.hayward@arm.com>
Date:   Mon Jul 8 10:00:25 2019 +0100

    Fix breakpoints on file reloads for PIE binaries
    
    When a binary is built using PIE, reloading the file will cause GDB to error
    on restart.  For example:
    gdb ./a.out
    (gdb) break main
    (gdb) run
    (gdb) file ./a.out
    (gdb) continue
    
    Will cause GDB to error with:
    Continuing.
    Warning:
    Cannot insert breakpoint 1.
    Cannot access memory at address 0x9e0
    Command aborted.
    
    This is due to the symbol offsets not being relocated after reloading the file.
    
    Fix is to ensure solib_create_inferior_hook is called, in the same manner as
    infrun.c:follow_exec().
    
    Expand the idempotent test to cover PIE scenarios.
    
    gdb/ChangeLog:
    
    	* symfile.c (symbol_file_command): Call solib_create_inferior_hook.
    
    gdb/testsuite/ChangeLog:
    
    	* gdb.base/break-idempotent.exp: Test both PIE and non PIE.

Diff:
---
 gdb/ChangeLog                               |  4 ++
 gdb/symfile.c                               | 12 ++++++
 gdb/testsuite/ChangeLog                     |  4 ++
 gdb/testsuite/gdb.base/break-idempotent.exp | 66 ++++++++++++++++-------------
 4 files changed, 56 insertions(+), 30 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index dfd1041..218bbf6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2019-08-04  Alan Hayward  <alan.hayward@arm.com>
+
+	* symfile.c (symbol_file_command): Call solib_create_inferior_hook.
+
 2019-07-04  Tom Tromey  <tom@tromey.com>
 
 	PR tui/24724:
diff --git a/gdb/symfile.c b/gdb/symfile.c
index 59647bf..dc6bdf3 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1672,7 +1672,19 @@ symbol_file_command (const char *args, int from_tty)
 
       validate_readnow_readnever (flags);
 
+      /* Set SYMFILE_DEFER_BP_RESET because the proper displacement for a PIE
+	 (Position Independent Executable) main symbol file will only be
+	 computed by the solib_create_inferior_hook below.  Without it,
+	 breakpoint_re_set would fail to insert the breakpoints with the zero
+	 displacement.  */
+      add_flags |= SYMFILE_DEFER_BP_RESET;
+
       symbol_file_add_main_1 (name, add_flags, flags, offset);
+
+      solib_create_inferior_hook (from_tty);
+
+      /* Now it's safe to re-add the breakpoints.  */
+      breakpoint_re_set ();
     }
 }
 
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 7631cce..a6d6843 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2019-07-08  Alan Hayward  <alan.hayward@arm.com>
+
+	* gdb.base/break-idempotent.exp: Test both PIE and non PIE.
+
 2019-07-04  Pedro Alves  <palves@redhat.com>
 
 	* lib/gdb.exp (foreach_with_prefix): Don't return early if
diff --git a/gdb/testsuite/gdb.base/break-idempotent.exp b/gdb/testsuite/gdb.base/break-idempotent.exp
index 902a5f8..96f91c5 100644
--- a/gdb/testsuite/gdb.base/break-idempotent.exp
+++ b/gdb/testsuite/gdb.base/break-idempotent.exp
@@ -36,23 +36,6 @@
 
 standard_testfile
 
-if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
-    return -1
-}
-
-if ![runto_main] then {
-    fail "can't run to main"
-    return 0
-}
-
-if [is_remote host] {
-    set arg [remote_download host $binfile]
-    if { $arg == "" } {
-	perror "download failed"
-	return -1
-    }
-}
-
 # Force a breakpoint re-set in GDB.  Currently this is done by
 # reloading symbols with the "file" command.
 
@@ -62,11 +45,11 @@ proc force_breakpoint_re_set {} {
     set test "file \$binfile"
     gdb_test_multiple "file $binfile" $test {
 	-re "Are you sure you want to change the file. .*y or n. $" {
-	    send_gdb "y\n"
+	    send_gdb "y\n" optional
 	    exp_continue
 	}
 	-re "Load new symbol table from \".*\".*y or n. $" {
-	    send_gdb "y\n"
+	    send_gdb "y\n" optional
 	    exp_continue
 	}
 	-re "Reading symbols from.*$gdb_prompt $" {
@@ -123,7 +106,7 @@ proc set_breakpoint { break_command } {
 proc test_break { always_inserted break_command } {
     set cmd [lindex [split "$break_command"] 0]
 
-    with_test_prefix "always-inserted $always_inserted: $cmd" {
+    with_test_prefix "$cmd" {
 	delete_breakpoints
 
 	if ![runto_main] then {
@@ -163,20 +146,43 @@ proc test_break { always_inserted break_command } {
     }
 }
 
-foreach always_inserted { "off" "on" } {
-    test_break $always_inserted "break"
+# The testcase uses the "file" command to force breakpoint re-set in
+# GDB.  Test both with and without PIE, as GDB used to mishandle
+# breakpoint re-set when reloading PIEs.
+foreach_with_prefix pie { "nopie" "pie" } {
+
+    set opts {debug}
+    lappend opts $pie
 
-    if {![skip_hw_breakpoint_tests]} {
-	test_break $always_inserted "hbreak"
+    set binfile [standard_output_file $testfile-$pie]
+
+    if {[prepare_for_testing "failed to prepare" $binfile $srcfile $opts]} {
+	continue
     }
 
-    if {![skip_hw_watchpoint_tests]} {
-	test_break $always_inserted "watch"
+    if [is_remote host] {
+	set arg [remote_download host $binfile]
+	if { $arg == "" } {
+	    untested "download failed"
+	    continue
+	}
     }
 
-    if {![skip_hw_watchpoint_access_tests]
-	&& ![skip_hw_watchpoint_multi_tests]} {
-	test_break $always_inserted "rwatch"
-	test_break $always_inserted "awatch"
+    foreach_with_prefix always_inserted { "off" "on" } {
+	test_break $always_inserted "break"
+
+	if {![skip_hw_breakpoint_tests]} {
+	    test_break $always_inserted "hbreak"
+	}
+
+	if {![skip_hw_watchpoint_tests]} {
+	    test_break $always_inserted "watch"
+	}
+
+	if {![skip_hw_watchpoint_access_tests]
+	    && ![skip_hw_watchpoint_multi_tests]} {
+	    test_break $always_inserted "rwatch"
+	    test_break $always_inserted "awatch"
+	}
     }
 }