forked from OSchip/llvm-project
13f6c81c5d
The current pattern matching for zext results in the following code snippet being produced, w1 = w0 r1 <<= 32 r1 >>= 32 Because BPF implementations require zero extension on 32bit loads this both adds a few extra unneeded instructions but also makes it a bit harder for the verifier to track the r1 register bounds. For example in this verifier trace we see at the end of the snippet R2 offset is unknown. However, if we track this correctly we see w1 should have the same bounds as r8. R8 smax is less than U32 max value so a zero extend load should keep the same value. Adding a max value of 800 (R8=inv(id=0,smax_value=800)) to an off=0, as seen in R7 should create a max offset of 800. However at the end of the snippet we note the R2 max offset is 0xffffFFFF. R0=inv(id=0,smax_value=800) R1_w=inv(id=0,umax_value=2147483647,var_off=(0x0; 0x7fffffff)) R6=ctx(id=0,off=0,imm=0) R7=map_value(id=0,off=0,ks=4,vs=1600,imm=0) R8_w=inv(id=0,smax_value=800,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R9=inv800 R10=fp0 fp-8=mmmm???? 58: (1c) w9 -= w8 59: (bc) w1 = w8 60: (67) r1 <<= 32 61: (77) r1 >>= 32 62: (bf) r2 = r7 63: (0f) r2 += r1 64: (bf) r1 = r6 65: (bc) w3 = w9 66: (b7) r4 = 0 67: (85) call bpf_get_stack#67 R0=inv(id=0,smax_value=800) R1_w=ctx(id=0,off=0,imm=0) R2_w=map_value(id=0,off=0,ks=4,vs=1600,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R3_w=inv(id=0,umax_value=800,var_off=(0x0; 0x3ff)) R4_w=inv0 R6=ctx(id=0,off=0,imm=0) R7=map_value(id=0,off=0,ks=4,vs=1600,imm=0) R8_w=inv(id=0,smax_value=800,umax_value=4294967295,var_off=(0x0; 0xffffffff)) R9_w=inv(id=0,umax_value=800,var_off=(0x0; 0x3ff)) R10=fp0 fp-8=mmmm???? After this patch R1 bounds are not smashed by the <<=32 >>=32 shift and we get correct bounds on R2 umax_value=800. Further it reduces 3 insns to 1. Signed-off-by: John Fastabend <john.fastabend@gmail.com> Differential Revision: https://reviews.llvm.org/D73985 |
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| llvm.spec.in | ||
README.txt
The LLVM Compiler Infrastructure ================================ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you are writing a package for LLVM, see docs/Packaging.rst for our suggestions.