2f1e6eb6c3
Ihor Solodrai reported a case ([1]) where gcc reports an error but clang ignores that error and proceeds to generate incorrect code. More specifically, the problematic code looks like: if r1 == 0xcafefeeddeadbeef goto <label> Here, 0xcafefeeddeadbeef needs to be encoded in a 32-bit imm field of the insns and the 32-bit imm allows sign extenstion to 64-bit imm. Obviously, 0xcafefeeddeadbeef cannot encode properly. The compilation failed for gcc with the following error: Error: immediate out of range, shall fit in 32 bits Given a 64-bit imm value, converting to the proper 32-bit imm value must satisfy the following 64-bit patterns: 00000000 00000000 00000000 00000000 xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx 11111111 11111111 11111111 11111111 1xxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx So if the top 32-bits is 0 or the top 33-bits is 0x1ffffffff, then the 64-bit imm value can be truncated into proper 32-bit imm. Otherwise, a warning message, the same as gcc, will be issued. If -Werror is enabled during compilation, the warning will turn into an error. [1] https://lore.kernel.org/bpf/70affb12-327b-4882-bd1d-afda8b8c6f56@linux.dev/
16 lines
539 B
LLVM
16 lines
539 B
LLVM
; RUN: llc -mtriple=bpfel -filetype=obj < %s 2>&1 >/dev/null | FileCheck %s
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; CHECK: warning: immediate out of range, shall fit in 32 bits
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define dso_local void @test_1() naked {
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tail call void asm sideeffect
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"r1 = 40; if r1 == 0x1deadbeef goto +0; r0 = 0; exit;", "~{r0},~{r1}"()
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unreachable
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}
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; CHECK: warning: immediate out of range, shall fit in 32 bits
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define dso_local void @test_2() naked {
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tail call void asm sideeffect
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"r1 = 40; if r1 == 0xffffffff00000000 goto +0; r0 = 0; exit;", "~{r0},~{r1}"()
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unreachable
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}
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