mirror of
https://github.com/golang/go
synced 2024-11-23 05:20:11 -07:00
359f44910f
Under certain circumstances, the existing rules for bit operations can
produce code that writes beyond its intended bounds. For example,
consider the following code:
func repro(b []byte, addr, bit int32) {
_ = b[3]
v := uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24 | 1<<(bit&31)
b[0] = byte(v)
b[1] = byte(v >> 8)
b[2] = byte(v >> 16)
b[3] = byte(v >> 24)
}
Roughly speaking:
1. The expression `1 << (bit & 31)` is rewritten into `(SHLL 1 bit)`
2. The expression `uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 |
uint32(b[3])<<24` is rewritten into `(MOVLload &b[0])`
3. The statements `b[0] = byte(v) ... b[3] = byte(v >> 24)` are
rewritten into `(MOVLstore &b[0], v)`
4. `(ORL (SHLL 1, bit) (MOVLload &b[0]))` is rewritten into
`(BTSL (MOVLload &b[0]) bit)`. This is a valid transformation because
the destination is a register: in this case, the bit offset is masked
by the number of bits in the destination register. This is identical
to the masking performed by `SHL`.
5. `(MOVLstore &b[0] (BTSL (MOVLload &b[0]) bit))` is rewritten into
`(BTSLmodify &b[0] bit)`. This is an invalid transformation because
the destination is memory: in this case, the bit offset is not
masked, and the chosen instruction may write outside its intended
32-bit location.
These changes fix the invalid rewrite performed in step (5) by
explicitly maksing the bit offset operand to `BT(S|R|C)(L|Q)modify`. In
the example above, the adjusted rules produce
`(BTSLmodify &b[0] (ANDLconst [31] bit))` in step (5).
These changes also add several new rules to rewrite bit sets, toggles,
and clears that are rooted at `(OR|XOR|AND)(L|Q)modify` operators into
appropriate `BT(S|R|C)(L|Q)modify` operators. These rules catch cases
where `MOV(L|Q)store ((OR|XOR|AND)(L|Q) ...)` is rewritten to
`(OR|XOR|AND)(L|Q)modify` before the `(OR|XOR|AND)(L|Q) ...` can be
rewritten to `BT(S|R|C)(L|Q) ...`.
Overall, compilecmp reports small improvements in code size on
darwin/amd64 when the changes to the compiler itself are exlcuded:
file before after Δ %
runtime.s 536464 536412 -52 -0.010%
bytes.s 32629 32593 -36 -0.110%
strings.s 44565 44529 -36 -0.081%
os/signal.s 7967 7959 -8 -0.100%
cmd/vendor/golang.org/x/sys/unix.s 81686 81678 -8 -0.010%
math/big.s 188235 188253 +18 +0.010%
cmd/link/internal/loader.s 89295 89056 -239 -0.268%
cmd/link/internal/ld.s 633551 633232 -319 -0.050%
cmd/link/internal/arm.s 18934 18928 -6 -0.032%
cmd/link/internal/arm64.s 31814 31801 -13 -0.041%
cmd/link/internal/riscv64.s 7347 7345 -2 -0.027%
cmd/compile/internal/ssa.s 4029173 4033066 +3893 +0.097%
total 21298280 21301472 +3192 +0.015%
Change-Id: I2e560548b515865129e1724e150e30540e9d29ce
GitHub-Last-Rev:
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| abi | ||
| alias3.dir | ||
| bench | ||
| chan | ||
| closure3.dir | ||
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| codegen | ||
| ddd2.dir | ||
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| interface | ||
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| retjmp.dir | ||
| runtime | ||
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| syntax | ||
| typeparam | ||
| uintptrescapes.dir | ||
| 64bit.go | ||
| 235.go | ||
| alg.go | ||
| alias1.go | ||
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| alias.go | ||
| align.go | ||
| append1.go | ||
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| args.go | ||
| armimm.go | ||
| assign1.go | ||
| assign.go | ||
| atomicload.go | ||
| bigalg.go | ||
| bigmap.go | ||
| blank1.go | ||
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| bom.go | ||
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| bounds.go | ||
| cannotassign.go | ||
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| checkbce.go | ||
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| closedchan.go | ||
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| cmp.go | ||
| cmplx.go | ||
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| cmplxdivide.c | ||
| cmplxdivide.go | ||
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| const1.go | ||
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| convert.go | ||
| convlit1.go | ||
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| copy1.go | ||
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| decl.go | ||
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| eof1.go | ||
| eof.go | ||
| escape2.go | ||
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| escape3.go | ||
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| escape5.go | ||
| escape_array.go | ||
| escape_calls.go | ||
| escape_closure.go | ||
| escape_field.go | ||
| escape_goto.go | ||
| escape_hash_maphash.go | ||
| escape_iface.go | ||
| escape_indir.go | ||
| escape_level.go | ||
| escape_map.go | ||
| escape_param.go | ||
| escape_runtime_atomic.go | ||
| escape_selfassign.go | ||
| escape_slice.go | ||
| escape_struct_param1.go | ||
| escape_struct_param2.go | ||
| escape_struct_return.go | ||
| escape_sync_atomic.go | ||
| escape_unsafe.go | ||
| escape.go | ||
| fibo.go | ||
| finprofiled.go | ||
| float_lit2.go | ||
| float_lit3.go | ||
| float_lit.go | ||
| floatcmp.go | ||
| for.go | ||
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| func3.go | ||
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| func5.go | ||
| func6.go | ||
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| func.go | ||
| funcdup2.go | ||
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| gc1.go | ||
| gc2.go | ||
| gc.go | ||
| gcgort.go | ||
| gcstring.go | ||
| goprint.go | ||
| goprint.out | ||
| goto.go | ||
| heapsampling.go | ||
| helloworld.go | ||
| helloworld.out | ||
| if.go | ||
| import1.go | ||
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| import.go | ||
| index0.go | ||
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| index.go | ||
| indirect1.go | ||
| indirect.go | ||
| init1.go | ||
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| initexp.go | ||
| initialize.go | ||
| initializerr.go | ||
| initloop.go | ||
| inline_big.go | ||
| inline_caller.go | ||
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| inline_literal.go | ||
| inline_math_bits_rotate.go | ||
| inline_sync.go | ||
| inline_variadic.go | ||
| inline.go | ||
| int_lit.go | ||
| intcvt.go | ||
| intrinsic_atomic.go | ||
| intrinsic.go | ||
| iota.go | ||
| label1.go | ||
| label.go | ||
| linkmain_run.go | ||
| linkmain.go | ||
| linkname2.go | ||
| linkname.go | ||
| linkobj.go | ||
| linkx_run.go | ||
| linkx.go | ||
| literal2.go | ||
| literal.go | ||
| live1.go | ||
| live2.go | ||
| live_syscall.go | ||
| live.go | ||
| locklinear.go | ||
| loopbce.go | ||
| mainsig.go | ||
| makechan.go | ||
| makemap.go | ||
| makenew.go | ||
| makeslice.go | ||
| mallocfin.go | ||
| map1.go | ||
| map.go | ||
| mapclear.go | ||
| maplinear.go | ||
| mergemul.go | ||
| method1.go | ||
| method2.go | ||
| method3.go | ||
| method4.go | ||
| method5.go | ||
| method6.go | ||
| method7.go | ||
| method.go | ||
| named1.go | ||
| named.go | ||
| nil.go | ||
| nilcheck.go | ||
| nilptr2.go | ||
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| nilptr.go | ||
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| peano.go | ||
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| prove.go | ||
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| README.md | ||
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| runtime.go | ||
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| sizeof.go | ||
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| solitaire.go | ||
| stack.go | ||
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| strength.go | ||
| string_lit.go | ||
| stringrange.go | ||
| struct0.go | ||
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| switch5.go | ||
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| switch.go | ||
| tinyfin.go | ||
| torture.go | ||
| turing.go | ||
| typecheck.go | ||
| typecheckloop.go | ||
| typeswitch1.go | ||
| typeswitch2.go | ||
| typeswitch2b.go | ||
| typeswitch3.go | ||
| typeswitch.go | ||
| uintptrescapes2.go | ||
| uintptrescapes3.go | ||
| uintptrescapes.go | ||
| undef.go | ||
| used.go | ||
| utf.go | ||
| varerr.go | ||
| varinit.go | ||
| winbatch.go | ||
| writebarrier.go | ||
| zerodivide.go | ||
The test directory contains tests of the Go tool chain and runtime. It includes black box tests, regression tests, and error output tests. They are run as part of all.bash.
To run just these tests, execute:
../bin/go run run.go
To run just tests from specified files in this directory, execute:
../bin/go run run.go -- file1.go file2.go ...
Standard library tests should be written as regular Go tests in the appropriate package.
The tool chain and runtime also have regular Go tests in their packages. The main reasons to add a new test to this directory are:
- it is most naturally expressed using the test runner; or
- it is also applicable to
gccgoand other Go tool chains.