* [Ada] Fix handling of load addresses for backtraces through SO
@ 2017-12-05 11:58 Pierre-Marie de Rodat
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From: Pierre-Marie de Rodat @ 2017-12-05 11:58 UTC (permalink / raw)
To: gcc-patches; +Cc: Olivier Hainque
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The processing of shared library load addresses for backtrace symbolization
suffers from disconnects between various parts in the runtime library regarding
where run-time vs shared-object-file-relative addresses are at hand.
At some points the code processes a local copy of each address coming from a
backtrace, adjusted by the load address when it comes from a shared library,
while other places keep referring to the run-time (unadjusted) address within
the backtrace array, at spots where module-relative addresses are needed as
well, e.g. when looking up debug info mmaped from the module file.
The first obvious "fix" idea for this would be to adjust the addresses in the
backtrace array as well, but we need to keep the unadjusted address someplace,
at least be able to display it to the user. It corresponds to real run-time
addresses that can be looked-up and examined while the process is running, so
is generally valuable.
This change introduces more explicit and systematic use of the load address
shift instead.
Tested on x86_64-pc-linux-gnu, committed on trunk
2017-12-05 Olivier Hainque <hainque@adacore.com>
libgnat/
* s-trasym__dwarf.adb (spec of Module_Name.Get): Instead of
possibly adjusting the lookup address by a load address, expect
a extra argument through which the load address can be conveyed
separately.
(Multi_Module_Symbolic_Traceback): Adjust accordingly. Pass the
retrieved load address to Init_Module.
* s-tsmona__linux.adb (Get): Honor the new interface.
* s-tsmona__mingw.adb (Get): Likewise.
* s-dwalin.ads: Adjust comments to be explicit about which
addresses are from module info and which are run-time addresses,
offsetted by the module load address.
* s-dwalin.adb (Set_Load_Address): Simply set C.Load_Slide.
Do not alter the module Low and High (relative) addresses.
(Is_Inside): Improve documentation regarding the kinds of addresses
at hand and correct the test.
(Symbolic_Traceback): Use separate variables with explicit names
for the address in traceback (run-time value) and the address to
lookup within the shared object (module-relative). Adjust the
computation of address passed to Symbolic_Address for symbolization.
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Index: libgnat/s-tsmona__mingw.adb
===================================================================
--- libgnat/s-tsmona__mingw.adb (revision 255408)
+++ libgnat/s-tsmona__mingw.adb (working copy)
@@ -50,15 +50,20 @@
-- Get --
---------
- function Get (Addr : access System.Address) return String is
+ function Get (Addr : System.Address;
+ Load_Addr : access System.Address)
+ return String
+ is
Res : DWORD;
hModule : aliased HANDLE;
Path : String (1 .. 1_024);
begin
+ Load_Addr.all := System.Null_Address;
+
if GetModuleHandleEx
(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS,
- Addr.all,
+ Addr,
hModule'Access) = Win32.TRUE
then
Res := GetModuleFileName (hModule, Path'Address, Path'Length);
Index: libgnat/s-tsmona__linux.adb
===================================================================
--- libgnat/s-tsmona__linux.adb (revision 255408)
+++ libgnat/s-tsmona__linux.adb (working copy)
@@ -32,8 +32,6 @@
-- This is the GNU/Linux specific version of this package
with Interfaces.C; use Interfaces.C;
-with System.Address_Operations; use System.Address_Operations;
-
separate (System.Traceback.Symbolic)
package body Module_Name is
@@ -134,7 +132,10 @@
-- Get --
---------
- function Get (Addr : access System.Address) return String is
+ function Get (Addr : System.Address;
+ Load_Addr : access System.Address)
+ return String
+ is
-- Dl_info record for Linux, used to get sym reloc offset
@@ -154,13 +155,15 @@
info : aliased Dl_info;
begin
- if dladdr (Addr.all, info'Access) /= 0 then
+ Load_Addr.all := System.Null_Address;
+ if dladdr (Addr, info'Access) /= 0 then
+
-- If we have a shared library we need to adjust the address to
-- be relative to the base address of the library.
if Is_Shared_Lib (info.dli_fbase) then
- Addr.all := SubA (Addr.all, info.dli_fbase);
+ Load_Addr.all := info.dli_fbase;
end if;
return Value (info.dli_fname);
Index: libgnat/s-trasym__dwarf.adb
===================================================================
--- libgnat/s-trasym__dwarf.adb (revision 255408)
+++ libgnat/s-trasym__dwarf.adb (working copy)
@@ -132,10 +132,12 @@
procedure Build_Cache_For_All_Modules;
-- Create the cache for all current modules
- function Get (Addr : access System.Address) return String;
- -- Returns the module name for the given address, Addr may be updated
- -- to be set relative to a shared library. This depends on the platform.
- -- Returns an empty string for the main executable.
+ function Get (Addr : System.Address;
+ Load_Addr : access System.Address) return String;
+ -- Returns the module name for the given address Addr, or an empty
+ -- string for the main executable. Load_Addr is set to the shared
+ -- library load address if this information is available, or to
+ -- System.Null_Address otherwise.
function Is_Supported return Boolean;
pragma Inline (Is_Supported);
@@ -499,12 +501,14 @@
-- Otherwise, try a shared library
declare
- Addr : aliased System.Address := Traceback (F);
- M_Name : constant String := Module_Name.Get (Addr'Access);
+ Load_Addr : aliased System.Address;
+ M_Name : constant String :=
+ Module_Name.Get (Addr => Traceback (F),
+ Load_Addr => Load_Addr'Access);
Module : Module_Cache;
Success : Boolean;
begin
- Init_Module (Module, Success, M_Name, System.Null_Address);
+ Init_Module (Module, Success, M_Name, Load_Addr);
if Success then
Multi_Module_Symbolic_Traceback
(Traceback,
Index: libgnat/s-dwalin.adb
===================================================================
--- libgnat/s-dwalin.adb (revision 255408)
+++ libgnat/s-dwalin.adb (working copy)
@@ -372,7 +372,8 @@
function Is_Inside (C : Dwarf_Context; Addr : Address) return Boolean is
begin
- return Addr >= C.Low and Addr <= C.High;
+ return (Addr >= To_Address (To_Integer (C.Low) + C.Load_Slide)
+ and Addr <= To_Address (To_Integer (C.High) + C.Load_Slide));
end Is_Inside;
---------
@@ -771,15 +772,7 @@
procedure Set_Load_Address (C : in out Dwarf_Context; Addr : Address) is
begin
- if Addr = Null_Address then
- return;
- else
- C.Load_Slide :=
- To_Integer (Addr) - Integer_Address (Get_Load_Address (C.Obj.all));
-
- C.Low := To_Address (To_Integer (C.Low) + C.Load_Slide);
- C.High := To_Address (To_Integer (C.High) + C.Load_Slide);
- end if;
+ C.Load_Slide := To_Integer (Addr);
end Set_Load_Address;
------------------
@@ -1523,9 +1516,11 @@
Res : in out System.Bounded_Strings.Bounded_String)
is
use Ada.Characters.Handling;
- C : Dwarf_Context := Cin;
- Addr : Address;
+ C : Dwarf_Context := Cin;
+ Addr_In_Traceback : Address;
+ Addr_To_Lookup : Address;
+
Dir_Name : Str_Access;
File_Name : Str_Access;
Subprg_Name : String_Ptr_Len;
@@ -1543,10 +1538,14 @@
-- If the buffer is full, no need to do any useless work
exit when Is_Full (Res);
- Addr := PC_For (Traceback (J));
+ Addr_In_Traceback := PC_For (Traceback (J));
+
+ Addr_To_Lookup := To_Address
+ (To_Integer (Addr_In_Traceback) - C.Load_Slide);
+
Symbolic_Address
(C,
- To_Address (To_Integer (Addr) + C.Load_Slide),
+ Addr_To_Lookup,
Dir_Name,
File_Name,
Subprg_Name,
@@ -1608,7 +1607,7 @@
if Suppress_Hex then
Append (Res, "...");
else
- Append_Address (Res, Addr);
+ Append_Address (Res, Addr_In_Traceback);
end if;
if Subprg_Name.Len > 0 then
Index: libgnat/s-dwalin.ads
===================================================================
--- libgnat/s-dwalin.ads (revision 255408)
+++ libgnat/s-dwalin.ads (working copy)
@@ -73,11 +73,11 @@
function Is_Inside (C : Dwarf_Context; Addr : Address) return Boolean;
pragma Inline (Is_Inside);
- -- Return true iff Addr is within the module
+ -- Return true iff a run-time address Addr is within the module
function Low (C : Dwarf_Context) return Address;
pragma Inline (Low);
- -- Return the lowest address of C
+ -- Return the lowest address of C, from the module object file
procedure Dump (C : in out Dwarf_Context);
-- Dump each row found in the object's .debug_lines section to standard out
@@ -165,7 +165,7 @@
type Dwarf_Context (In_Exception : Boolean := False) is record
Load_Slide : System.Storage_Elements.Integer_Address := 0;
Low, High : Address;
- -- Bounds of the module
+ -- Bounds of the module, per the module object file
Obj : SOR.Object_File_Access;
-- The object file containing dwarf sections
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2017-12-05 11:58 [Ada] Fix handling of load addresses for backtraces through SO Pierre-Marie de Rodat
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