[compiler-rt] [tsan] Shrink RiscV64 48-bit LowApp region slightly to speed up TSan RestoreAddr (PR #72316)
Thurston Dang via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 14 13:59:06 PST 2023
https://github.com/thurstond created https://github.com/llvm/llvm-project/pull/72316
The RiscV64 48-bit mappings introduced in 46cb8d9a325233ac11ed5e90367c43774294d87e necessitated changing RestoreAddr to use 4-bits as the indicator. This roughly halves the speed of RestoreAddr, because it is now brute-force testing addresses in 1TB increments, rather than 2TB increments. Crucially, this slowdown applies to TSan on all platforms, not just RiscV64 48-bit.
This patch slightly shrinks the RiscV64 48-bit LowApp region mapping (from 5TB to 4TB); we hope that 4TB ought to be enough for anybody, especially since there is no ASLR applied to the binary in this region. This allows restoring RestoreAddr to use 3-bits as the indicator again, thus speeding up TSan on all platforms.
>From 0e164185d0c2d598c6a17ae8dcd56b93adfcaa2b Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Tue, 14 Nov 2023 21:56:59 +0000
Subject: [PATCH] [tsan] Shrink RiscV64 48-bit LowApp region slightly to speed
up TSan RestoreAddr
The RiscV64 48-bit mappings introduced in 46cb8d9a325233ac11ed5e90367c43774294d87e necessitated changing RestoreAddr to use 4-bits as the indicator. This roughly halves the speed of RestoreAddr, because it is now brute-force testing addresses in 1TB increments, rather than 2TB increments. Crucially, this slowdown applies to TSan on all platforms, not just RiscV64 48-bit.
This patch slightly shrinks the RiscV64 48-bit LowApp region mapping (from 5TB to 4TB); we hope that 4TB ought to be enough for anybody, especially since there is no ASLR applied to the binary in this region. This allows restoring RestoreAddr to use 3-bits as the indicator again, thus speeding up TSan on all platforms.
---
compiler-rt/lib/tsan/rtl/tsan_platform.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/compiler-rt/lib/tsan/rtl/tsan_platform.h b/compiler-rt/lib/tsan/rtl/tsan_platform.h
index d9ed3979b69eaf5..70b9ae09a990420 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_platform.h
+++ b/compiler-rt/lib/tsan/rtl/tsan_platform.h
@@ -413,18 +413,18 @@ struct MappingRiscv64_39 {
/*
C/C++ on linux/riscv64 (48-bit VMA)
-0000 0000 1000 - 0500 0000 0000: main binary ( 5 TB)
+0000 0000 1000 - 0400 0000 0000: main binary ( 4 TB)
0500 0000 0000 - 2000 0000 0000: -
2000 0000 0000 - 4000 0000 0000: shadow memory (32 TB)
4000 0000 0000 - 4800 0000 0000: metainfo ( 8 TB)
4800 0000 0000 - 5555 5555 5000: -
5555 5555 5000 - 5a00 0000 0000: main binary (PIE) (~5 TB)
5a00 0000 0000 - 7a00 0000 0000: -
-7a00 0000 0000 - 7fff ffff ffff: libraries and main thread stack ( 5 TB)
+7a00 0000 0000 - 7fff ffff ffff: libraries and main thread stack ( 6 TB)
*/
struct MappingRiscv64_48 {
static const uptr kLoAppMemBeg = 0x000000001000ull;
- static const uptr kLoAppMemEnd = 0x050000000000ull;
+ static const uptr kLoAppMemEnd = 0x040000000000ull;
static const uptr kShadowBeg = 0x200000000000ull;
static const uptr kShadowEnd = 0x400000000000ull;
static const uptr kMetaShadowBeg = 0x400000000000ull;
@@ -967,7 +967,7 @@ struct RestoreAddrImpl {
Mapping::kMidAppMemEnd, Mapping::kHiAppMemBeg, Mapping::kHiAppMemEnd,
Mapping::kHeapMemBeg, Mapping::kHeapMemEnd,
};
- const uptr indicator = 0x0f0000000000ull;
+ const uptr indicator = 0x0e0000000000ull;
const uptr ind_lsb = 1ull << LeastSignificantSetBitIndex(indicator);
for (uptr i = 0; i < ARRAY_SIZE(ranges); i += 2) {
uptr beg = ranges[i];
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