Fix resolving GNU ifunc bp locations when inferior runs resolver

I noticed that if you set a breakpoint on an ifunc before the ifunc is
resolved, and then let the program call the ifunc, thus resolving it,
GDB end up with a location for that original breakpoint that is
pointing to the ifunc target, but it is left pointing to the first
address of the function, instead of after its prologue.  After
prologue is what you get if you create a new breakpoint at that point.

1) With no debug info for the target function:

  1.a) Set before resolving, and then program continued passed resolving:

    Num     Type           Disp Enb Address            What
    1       breakpoint     keep y   0x0000000000400753 <final>

  1.b) Breakpoint set after inferior resolved ifunc:

    Num     Type           Disp Enb Address            What
    2       breakpoint     keep y   0x0000000000400757 <final+4>

2) With debug info for the target function:

   1.a) Set before resolving, and then program continued passed resolving:

     Num     Type           Disp Enb Address            What
     1       breakpoint     keep y   0x0000000000400753 in final at gdb/testsuite/gdb.base/gnu-ifunc-final.c:20

   1.b) Breakpoint set after inferior resolved ifunc:

     Num     Type           Disp Enb Address            What
     2       breakpoint     keep y   0x000000000040075a in final at gdb/testsuite/gdb.base/gnu-ifunc-final.c:21

The problem is that elf_gnu_ifunc_resolver_return_stop (called by the
internal breakpoint that traps the resolver returning) does not agree
with linespec.c:minsym_found.  It does not skip to the function's
start line (i.e., past the prologue).  We can now use the
find_function_start_sal overload added by the previous commmit to fix
this.

New tests included, which fail before the patch, and pass afterwards.

gdb/ChangeLog:
2018-04-26  Pedro Alves  <palves@redhat.com>

	* elfread.c (elf_gnu_ifunc_resolver_return_stop): Use
	find_function_start_sal instead of find_pc_line.

gdb/testsuite/ChangeLog:
2018-04-26  Pedro Alves  <palves@redhat.com>

	* gdb.base/gnu-ifunc.exp (set-break): Test that GDB resolves
	ifunc breakpoint locations correctly of ifunc breakpoints set
	while the program resolves the ifunc.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 59168894f98857f7691105b202baafa532d752eb..6164fc373a1c2f4812359def87b068716d0b247e 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-04-26  Pedro Alves  <palves@redhat.com>
+
+       * elfread.c (elf_gnu_ifunc_resolver_return_stop): Use
+       find_function_start_sal instead of find_pc_line.
+
 2018-04-26  Pedro Alves  <palves@redhat.com>
 
        * breakpoint.c (set_breakpoint_location_function): Handle

diff --git a/gdb/elfread.c b/gdb/elfread.c
index e724f347b9638b50b9f5c0e432058940edb5b803..e7925a3bc443a8a58b30d55a4db714552fb7e047 100644 (file)
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -1026,7 +1026,8 @@ elf_gnu_ifunc_resolver_return_stop (struct breakpoint *b)
 
   b->type = bp_breakpoint;
   update_breakpoint_locations (b, current_program_space,
-                              find_pc_line (resolved_pc, 0), {});
+                              find_function_start_sal (resolved_pc, NULL, true),
+                              {});
 }
 
 /* A helper function for elf_symfile_read that reads the minimal

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 29ae9b27c4a8c2fdf76100db217fc8e4d95ad62a..34da102c626ea004f3390bd1539d57e92d3d6a79 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2018-04-26  Pedro Alves  <palves@redhat.com>
+
+       * gdb.base/gnu-ifunc.exp (set-break): Test that GDB resolves
+       ifunc breakpoint locations correctly of ifunc breakpoints set
+       while the program resolves the ifunc.
+
 2018-04-26  Pedro Alves  <palves@redhat.com>
 
        * gdb.base/gnu-ifunc-final.c: New file.

diff --git a/gdb/testsuite/gdb.base/gnu-ifunc.exp b/gdb/testsuite/gdb.base/gnu-ifunc.exp
index 827ac1202d2224dc73eebb5c88cd126386388aec..d6ec6988a7d75668d06094414595652c5d401c29 100644 (file)
--- a/gdb/testsuite/gdb.base/gnu-ifunc.exp
+++ b/gdb/testsuite/gdb.base/gnu-ifunc.exp
@@ -106,6 +106,9 @@ proc_with_prefix set-break {resolver_attr resolver_debug final_debug} {
        return 1
     }
 
+    gdb_breakpoint [gdb_get_line_number "break-at-call"]
+    gdb_continue_to_breakpoint "break-at-call" ".*break-at-call.*"
+
     set ws "\[ \t\]+"
     set dot "\\.?"
 
@@ -131,19 +134,21 @@ proc_with_prefix set-break {resolver_attr resolver_debug final_debug} {
            "Breakpoint $decimal at gnu-indirect-function resolver at $hex"
        gdb_test "info breakpoints" \
            "$decimal${ws}STT_GNU_IFUNC resolver${ws}keep${ws}y${ws}$hex <${gnu_ifunc_resolver}>"
+
+       # Make the breakpoint conditional on a condition that always
+       # fails.  This is so that when the ifunc-resolver breakpoint
+       # triggers, GDB resumes the program immediately.
+       gdb_test_no_output "condition \$bpnum 0"
     }
 
     global final_src
 
     with_test_prefix "resolve" {
-       delete_breakpoints
        gdb_breakpoint [gdb_get_line_number "break-at-exit"]
        gdb_continue_to_breakpoint "break-at-exit" ".*break-at-exit.*"
     }
 
     with_test_prefix "after resolving" {
-       delete_breakpoints
-
        if {!$final_debug} {
            # Set a breakpoint both at the ifunc, and at the ifunc's
            # target.  GDB should resolve both to the same address.
@@ -176,7 +181,12 @@ proc_with_prefix set-break {resolver_attr resolver_debug final_debug} {
            gdb_test "break gnu_ifunc" "Breakpoint .* at $hex: file .*$final_src, line $lineno\\."
            set location "$decimal${ws}breakpoint${ws}keep${ws}y${ws}$hex in final at .*$final_src:$lineno"
        }
-       gdb_test "info breakpoints" "$location\r\n$location"
+
+       # The first location here is for the breakpoint that was set
+       # before the ifunc was resolved.  It should be resolved by
+       # now, and it should have the exact same address/line as the
+       # other two locations.
+       gdb_test "info breakpoints" "$location\r\n.*$location\r\n$location"
     }
 }