mirror of
https://gitee.com/openharmony/third_party_jsoncpp
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127 lines
4.6 KiB
Diff
127 lines
4.6 KiB
Diff
From 42e892d96e47b1f6e29844cc705e148ec4856448 Mon Sep 17 00:00:00 2001
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From: Jessica Clarke <jrtc27@jrtc27.com>
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Date: Wed, 12 Jan 2022 21:27:16 +0000
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Subject: [PATCH] Use default rather than hard-coded 8 for maximum aggregate
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member alignment (#1378)
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On CHERI, and thus Arm's Morello prototype, pointers are represented as
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hardware capabilities. These capabilities are comprised of not just an
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integer address, as is the representation for traditional pointers, but
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also bounds, permissions and other metadata, plus a tag bit used as the
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validity bit, which provides fine-grained spatial and referential safety
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for C and C++ in hardware. This tag bit is not part of the data itself
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and is instead kept on the side, flowing with the capability between
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registers and the memory subsystem, and any attempt to amplify the
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privilege of or corrupt a capability clears this tag (or, in some cases,
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traps), rendering them impossible to forge; you can only create
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capabilities that are (possibly trivial) subsets of existing ones.
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When the capability is stored in memory, this tag bit needs to be
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preserved, which is done through the use of tagged memory. Every
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capability-sized word gains an additional non-addressable (from the
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CPU's perspective; depending on the implementation the tag bits may be
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stored in a small block of memory carved out of normal DRAM that the CPU
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is blocked from accessing) bit. This means that capabilities can only be
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stored to aligned locations; attempting to store them to unaligned
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locations will trap with an alignment fault or, if you end up using a
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memcpy call, will copy the raw bytes of the capability's representation
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but lose the tag, so when it is eventually loaded back as a capability
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and dereferenced it will fault.
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Since, on 64-bit architectures, our capabilities, used to implement C
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language pointers, are 128-bit quantities, this means they need 16-byte
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alignment. Currently the various #pragma pack directives, used to work
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around (extremely broken and bogus) code that includes jsoncpp in a
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context where the maximum alignment has been overridden, hard-code 8 as
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the maximum alignment to use, and so do not sufficiently align CHERI /
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Morello capabilities on 64-bit architectures. On Windows x64, the
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default is also not 8 but 16 (ARM64 is supposedly 8), so this is
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slightly dodgy to do there too, but in practice likely not an issue so
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long as you don't use any 128-bit types there.
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Instead of hard-coding a width, use a directive that resets the packing
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back to the default. Unfortunately, whilst GCC and Clang both accept
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using #pragma pack(push, 0) as shorthand like for any non-zero value,
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MSVC does not, so this needs to be two directives.
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---
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include/json/allocator.h | 3 ++-
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include/json/json_features.h | 3 ++-
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include/json/reader.h | 3 ++-
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include/json/value.h | 3 ++-
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include/json/writer.h | 3 ++-
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5 files changed, 10 insertions(+), 5 deletions(-)
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diff --git a/include/json/allocator.h b/include/json/allocator.h
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index 95ef8a5..7540642 100644
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--- a/include/json/allocator.h
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+++ b/include/json/allocator.h
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@@ -9,7 +9,8 @@
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#include <cstring>
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#include <memory>
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-#pragma pack(push, 8)
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+#pragma pack(push)
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+#pragma pack()
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namespace Json {
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template <typename T> class SecureAllocator {
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diff --git a/include/json/json_features.h b/include/json/json_features.h
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index 7c7e9f5..e4a61d6 100644
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--- a/include/json/json_features.h
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+++ b/include/json/json_features.h
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@@ -10,7 +10,8 @@
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#include "forwards.h"
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#endif // if !defined(JSON_IS_AMALGAMATION)
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-#pragma pack(push, 8)
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+#pragma pack(push)
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+#pragma pack()
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namespace Json {
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diff --git a/include/json/reader.h b/include/json/reader.h
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index be0d767..46975d8 100644
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--- a/include/json/reader.h
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+++ b/include/json/reader.h
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@@ -23,7 +23,8 @@
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#pragma warning(disable : 4251)
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#endif // if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
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-#pragma pack(push, 8)
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+#pragma pack(push)
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+#pragma pack()
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namespace Json {
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diff --git a/include/json/value.h b/include/json/value.h
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index 0edeb05..57ecb13 100644
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--- a/include/json/value.h
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+++ b/include/json/value.h
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@@ -53,7 +53,8 @@
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#pragma warning(disable : 4251 4275)
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#endif // if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
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-#pragma pack(push, 8)
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+#pragma pack(push)
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+#pragma pack()
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/** \brief JSON (JavaScript Object Notation).
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*/
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diff --git a/include/json/writer.h b/include/json/writer.h
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index 03f9906..7d8cf4d 100644
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--- a/include/json/writer.h
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+++ b/include/json/writer.h
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@@ -20,7 +20,8 @@
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#pragma warning(disable : 4251)
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#endif // if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
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-#pragma pack(push, 8)
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+#pragma pack(push)
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+#pragma pack()
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namespace Json {
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--
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2.42.0.windows.2
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