The fix for PR123457 to fix PCH was only partial. While it added the table
pointers to GTY so they're tracked as roots, it didn't fix the pointers of the
nested classes that are used as hashes for the object.
This leads to the PCH tests all still crashing when the toolchain is configured
with -PIE.
There are three pointers being used in function_instance::hash ()
const char *base_name;
const function_base *base;
const function_shape *shape;
These points when PIE and PCH will be loaded into different offsets by each
invocation of the compiler sharing the same PCH file since these pointer point
into the compiler's executable and are no objects allocated by GGC.
The documentation states that GTY((callback)) can only be used for function
pointers so can't be used for data pointers. The base class is marked
GTY((user)) anyway. The easiest fix is dropping the pointers from the
calculation of the hash, however this weakens the hash function.
Instead this patch registers the pointers with the walkers through
gt_pch_note_callback and then instead of using the pointers in the hash it uses
the stable ptr diff between an anchor and the pointer.
The idea is that as the executable gets loaded into different addresses, since
PCH enforced that it must be the exact same version of the binary that the
offsets are constant. So by storing the ptr - offset we get a stable "hash" ID.
The anchor here is chosen to be the function_table itself which is being
relocated by PCH.
Bootstrapped Regtested on aarch64-none-linux-gnu with and
wihtout --enable-host-pie and no issues.
Ok for master? and backport to active all branches?
Thanks,
Tamar
gcc/ChangeLog:
PR target/20957
* config/aarch64/aarch64-acle-builtins.cc (function_instance::hash):
Use ptr diff for hash instead of ptr.
(gt_pch_nx): Add the pointers to PCH tracking.
---
diff --git a/gcc/config/aarch64/aarch64-acle-builtins.cc
b/gcc/config/aarch64/aarch64-acle-builtins.cc
index
5a063fb46ebbc6818c6db00781799c0fc1a5c79a..9841ae941685db577421081cb9eb360a21cbcbf6
100644
--- a/gcc/config/aarch64/aarch64-acle-builtins.cc
+++ b/gcc/config/aarch64/aarch64-acle-builtins.cc
@@ -456,8 +456,10 @@ function_instance::hash () const
{
inchash::hash h;
/* BASE uniquely determines BASE_NAME, so we don't need to hash both. */
- h.add_ptr (base);
- h.add_ptr (shape);
+ /* FUNCTION_TABLE has a fixed address relative to BASE and SHAPE within
+ the compiler binary, even if PIE changes the binary's load address. */
+ h.add_hwi ((uintptr_t) base - (uintptr_t) &function_table);
+ h.add_hwi ((uintptr_t) shape - (uintptr_t) &function_table);
h.add_int (mode_suffix_id);
h.add_int (type_suffix_ids[0]);
h.add_int (type_suffix_ids[1]);
@@ -4681,8 +4683,14 @@ gt_pch_nx (function_instance *)
}
inline void
-gt_pch_nx (function_instance *, gt_pointer_operator, void *)
-{
+gt_pch_nx (function_instance *instance, gt_pointer_operator, void *)
+{
+ /* The instance is the first member of its containing GC object. PCH
+ adjusts these pointers if the compiler has a different PIE load base. */
+ static_assert (offsetof (registered_function, instance) == 0);
+ gt_pch_note_callback (&instance->base_name, instance);
+ gt_pch_note_callback (&instance->base, instance);
+ gt_pch_note_callback (&instance->shape, instance);
}
#include "gt-aarch64-acle-builtins.h"
--
diff --git a/gcc/config/aarch64/aarch64-acle-builtins.cc b/gcc/config/aarch64/aarch64-acle-builtins.cc
index 5a063fb46ebbc6818c6db00781799c0fc1a5c79a..9841ae941685db577421081cb9eb360a21cbcbf6 100644
--- a/gcc/config/aarch64/aarch64-acle-builtins.cc
+++ b/gcc/config/aarch64/aarch64-acle-builtins.cc
@@ -456,8 +456,10 @@ function_instance::hash () const
{
inchash::hash h;
/* BASE uniquely determines BASE_NAME, so we don't need to hash both. */
- h.add_ptr (base);
- h.add_ptr (shape);
+ /* FUNCTION_TABLE has a fixed address relative to BASE and SHAPE within
+ the compiler binary, even if PIE changes the binary's load address. */
+ h.add_hwi ((uintptr_t) base - (uintptr_t) &function_table);
+ h.add_hwi ((uintptr_t) shape - (uintptr_t) &function_table);
h.add_int (mode_suffix_id);
h.add_int (type_suffix_ids[0]);
h.add_int (type_suffix_ids[1]);
@@ -4681,8 +4683,14 @@ gt_pch_nx (function_instance *)
}
inline void
-gt_pch_nx (function_instance *, gt_pointer_operator, void *)
-{
+gt_pch_nx (function_instance *instance, gt_pointer_operator, void *)
+{
+ /* The instance is the first member of its containing GC object. PCH
+ adjusts these pointers if the compiler has a different PIE load base. */
+ static_assert (offsetof (registered_function, instance) == 0);
+ gt_pch_note_callback (&instance->base_name, instance);
+ gt_pch_note_callback (&instance->base, instance);
+ gt_pch_note_callback (&instance->shape, instance);
}
#include "gt-aarch64-acle-builtins.h"
