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[gwp-asan] Initialize AllocatorVersionMagic at runtime

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GWP-ASan's `AllocatorState` was recently extended with a
`AllocatorVersionMagic` structure required so that GWP-ASan bug reports
can be understood by tools at different versions.

On Fuchsia, this in included in the `scudo::Allocator` structure, and
by having non-zero initializers, this effectively moved the static
allocator structure from the `.bss` segment to the `.data` segment, thus
increasing (significantly) the size of the libc.

This CL proposes to initialize the structure with its magic numbers at
runtime, allowing for the allocator to go back into the `.bss` segment.

I will work on adding a test on the Scudo side to ensure that this type
of changes get detected early on. Additional work is also needed to
reduce the footprint of the (large) memory-tagging related structures
that are currently part of the allocator.

Differential Revision: https://reviews.llvm.org/D110575
This commit is contained in:
Kostya Kortchinsky 2021-09-27 12:31:59 -07:00
parent ee6228ff8c
commit 04f5913395
2 changed files with 19 additions and 6 deletions
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18
compiler-rt/lib/gwp_asan/common.h
View file

@ -22,16 +22,22 @@ namespace gwp_asan {
// Magic header that resides in the AllocatorState so that GWP-ASan bugreports
// can be understood by tools at different versions. Out-of-process crash
// handlers, like crashpad on Fuchsia, take the raw conents of the
// handlers, like crashpad on Fuchsia, take the raw contents of the
// AllocationMetatada array and the AllocatorState, and shove them into the
// minidump. Online unpacking of these structs needs to know from which version
// of GWP-ASan its extracting the information, as the structures are not stable.
// of GWP-ASan it's extracting the information, as the structures are not
// stable.
struct AllocatorVersionMagic {
const uint8_t Magic[4] = {'A', 'S', 'A', 'N'};
// The values are copied into the structure at runtime, during
// `GuardedPoolAllocator::init()` so that GWP-ASan remains completely in the
// `.bss` segment.
static constexpr uint8_t kAllocatorVersionMagic[4] = {'A', 'S', 'A', 'N'};
uint8_t Magic[4] = {};
// Update the version number when the AllocatorState or AllocationMetadata
// change.
const uint16_t Version = 1;
const uint16_t Reserved = 0;
static constexpr uint16_t kAllocatorVersion = 1;
uint16_t Version = 0;
uint16_t Reserved = 0;
};
enum class Error : uint8_t {
@ -99,7 +105,7 @@ struct AllocationMetadata {
// set of information required for understanding a GWP-ASan crash.
struct AllocatorState {
constexpr AllocatorState() {}
const AllocatorVersionMagic VersionMagic{};
AllocatorVersionMagic VersionMagic{};
// Returns whether the provided pointer is a current sampled allocation that
// is owned by this pool.

7
compiler-rt/lib/gwp_asan/guarded_pool_allocator.cpp
View file

@ -59,6 +59,13 @@ void GuardedPoolAllocator::init(const options::Options &Opts) {
SingletonPtr = this;
Backtrace = Opts.Backtrace;
State.VersionMagic = {{AllocatorVersionMagic::kAllocatorVersionMagic[0],
AllocatorVersionMagic::kAllocatorVersionMagic[1],
AllocatorVersionMagic::kAllocatorVersionMagic[2],
AllocatorVersionMagic::kAllocatorVersionMagic[3]},
AllocatorVersionMagic::kAllocatorVersion,
0};
State.MaxSimultaneousAllocations = Opts.MaxSimultaneousAllocations;
const size_t PageSize = getPlatformPageSize();