bpf: gas: consolidate handling of immediate overflows
This commit changes the BPF GAS port in order to handle immediate overflows the same way than the clang BPF assembler: - For an immediate field of N bits, any written number (positive or negative) whose two's complement encoding fit in N its is accepted. This means that -2 is the same than 0xffffffe. It is up to the instructions to decide how to interpret the encoded value. - Immediate fields in jump instructions are no longer relaxed. Relaxing to jump instructions with wider range is only performed when expressions are involved. - The manual is updated to document this, and testsuite adapted accordingly. Tested in x86_64-linux-gnu host, bpf-unknown-none target. gas/ChangeLog: 2023-08-17 Jose E. Marchesi <jose.marchesi@oracle.com> * config/tc-bpf.c (check_immediate_overflow): New function. (encode_insn): Use check_immediate_overflow. (md_assemble): Do not relax instructions with constant disp16 fields. * doc/c-bpf.texi (BPF Instructions): Add note about how numerical literal values are interpreted for instruction immediate operands. * testsuite/gas/bpf/disp16-overflow.s: Adapt accordingly. * testsuite/gas/bpf/jump-relax-jump.s: Likewise. * testsuite/gas/bpf/jump-relax-jump.d: Likewise. * testsuite/gas/bpf/jump-relax-jump-be.d: Likewise. * testsuite/gas/bpf/jump-relax-ja.s: Likewise. * testsuite/gas/bpf/jump-relax-ja.d: Likewise. * testsuite/gas/bpf/jump-relax-ja-be.d: Likewise. * testsuite/gas/bpf/disp16-overflow-relax.l: Likewise. * testsuite/gas/bpf/imm32-overflow.s: Likewise. * testsuite/gas/bpf/disp32-overflow.s: Likewise. * testsuite/gas/bpf/disp16-overflow.l: Likewise. * testsuite/gas/bpf/disp32-overflow.l: Likewise. * testsuite/gas/bpf/imm32-overflow.l: Likewise. * testsuite/gas/bpf/offset16-overflow.l: Likewise.
This commit is contained in:
Jose E. Marchesi
parent
646657284f
commit
5be1b78727
@ -1,3 +1,26 @@
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2023-08-17 Jose E. Marchesi <jose.marchesi@oracle.com>
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* config/tc-bpf.c (check_immediate_overflow): New function.
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(encode_insn): Use check_immediate_overflow.
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(md_assemble): Do not relax instructions with
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constant disp16 fields.
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* doc/c-bpf.texi (BPF Instructions): Add note about how numerical
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literal values are interpreted for instruction immediate operands.
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* testsuite/gas/bpf/disp16-overflow.s: Adapt accordingly.
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* testsuite/gas/bpf/jump-relax-jump.s: Likewise.
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* testsuite/gas/bpf/jump-relax-jump.d: Likewise.
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* testsuite/gas/bpf/jump-relax-jump-be.d: Likewise.
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* testsuite/gas/bpf/jump-relax-ja.s: Likewise.
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* testsuite/gas/bpf/jump-relax-ja.d: Likewise.
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* testsuite/gas/bpf/jump-relax-ja-be.d: Likewise.
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* testsuite/gas/bpf/disp16-overflow-relax.l: Likewise.
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* testsuite/gas/bpf/imm32-overflow.s: Likewise.
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* testsuite/gas/bpf/disp32-overflow.s: Likewise.
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* testsuite/gas/bpf/disp16-overflow.l: Likewise.
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* testsuite/gas/bpf/disp32-overflow.l: Likewise.
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* testsuite/gas/bpf/imm32-overflow.l: Likewise.
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* testsuite/gas/bpf/offset16-overflow.l: Likewise.
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2023-07-30 Jose E. Marchesi <jose.marchesi@oracle.com>
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* config/tc-bpf.h (elf_tc_final_processing): Define.
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@ -286,6 +286,26 @@ signed_overflow (offsetT value, unsigned bits)
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return (value < -lim || value >= lim);
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}
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/* Return non-zero if the two's complement encoding of VALUE would
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overflow an immediate field of width BITS bits. */
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static bool
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immediate_overflow (int64_t value, unsigned bits)
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{
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if (value < 0)
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return signed_overflow (value, bits);
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else
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{
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valueT lim;
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if (bits >= sizeof (valueT) * 8)
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return false;
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lim = (valueT) 1 << bits;
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return ((valueT) value >= lim);
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}
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}
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/* Functions concerning relocs. */
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@ -379,7 +399,7 @@ tc_gen_reloc (asection *sec ATTRIBUTE_UNUSED, fixS *fixP)
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#define RELAX_BRANCH_UNCOND(i) (((i) & 1) != 0)
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/* Compute the length of a branch seuqence, and adjust the stored
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/* Compute the length of a branch sequence, and adjust the stored
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length accordingly. If FRAG is NULL, the worst-case length is
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returned. */
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@ -854,7 +874,8 @@ md_apply_fix (fixS *fixP, valueT *valP, segT seg ATTRIBUTE_UNUSED)
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immediates are encoded as zeroes. */
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static void
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encode_insn (struct bpf_insn *insn, char *bytes, int relaxed)
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encode_insn (struct bpf_insn *insn, char *bytes,
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int relaxed ATTRIBUTE_UNUSED)
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{
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uint8_t src, dst;
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@ -911,8 +932,8 @@ encode_insn (struct bpf_insn *insn, char *bytes, int relaxed)
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{
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int64_t imm = insn->imm32.X_add_number;
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if (signed_overflow (imm, 32))
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as_bad (_("signed immediate out of range, shall fit in 32 bits"));
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if (immediate_overflow (imm, 32))
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as_bad (_("immediate out of range, shall fit in 32 bits"));
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else
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encode_int32 (insn->imm32.X_add_number, bytes + 4);
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}
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@ -921,8 +942,8 @@ encode_insn (struct bpf_insn *insn, char *bytes, int relaxed)
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{
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int64_t disp = insn->disp32.X_add_number;
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if (signed_overflow (disp, 32))
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as_bad (_("signed pc-relative offset out of range, shall fit in 32 bits"));
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if (immediate_overflow (disp, 32))
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as_bad (_("pc-relative offset out of range, shall fit in 32 bits"));
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else
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encode_int32 (insn->disp32.X_add_number, bytes + 4);
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}
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@ -931,8 +952,8 @@ encode_insn (struct bpf_insn *insn, char *bytes, int relaxed)
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{
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int64_t offset = insn->offset16.X_add_number;
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if (signed_overflow (offset, 16))
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as_bad (_("signed pc-relative offset out of range, shall fit in 16 bits"));
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if (immediate_overflow (offset, 16))
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as_bad (_("pc-relative offset out of range, shall fit in 16 bits"));
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else
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encode_int16 (insn->offset16.X_add_number, bytes + 2);
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}
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@ -941,8 +962,8 @@ encode_insn (struct bpf_insn *insn, char *bytes, int relaxed)
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{
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int64_t disp = insn->disp16.X_add_number;
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if (!relaxed && signed_overflow (disp, 16))
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as_bad (_("signed pc-relative offset out of range, shall fit in 16 bits"));
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if (immediate_overflow (disp, 16))
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as_bad (_("pc-relative offset out of range, shall fit in 16 bits"));
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else
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encode_int16 (insn->disp16.X_add_number, bytes + 2);
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}
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@ -1517,7 +1538,7 @@ md_assemble (char *str ATTRIBUTE_UNUSED)
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break;
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}
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insn.has_disp16 = 1;
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insn.is_relaxable = 1;
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insn.is_relaxable = (insn.disp16.X_op != O_constant);
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p += 4;
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}
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else if (strncmp (p, "%d32", 4) == 0)
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@ -844,7 +844,7 @@ struct pop_entry pop_table[] =
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{
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{ "hix", BFD_RELOC_SPARC_HIX22, F_POP_V9 },
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{ "lox", BFD_RELOC_SPARC_LOX10, F_POP_V9 },
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{ "hi", BFD_RELOC_HI22, F_POP_PCREL },
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{ "hi"5, BFD_RELOC_HI22, F_POP_PCREL },
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{ "lo", BFD_RELOC_LO10, F_POP_PCREL },
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{ "pc22", BFD_RELOC_SPARC_PC22, F_POP_PCREL },
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{ "pc10", BFD_RELOC_SPARC_PC10, F_POP_PCREL },
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@ -172,6 +172,14 @@ Signed 32-bit immediate.
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Signed 64-bit immediate.
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@end table
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@noindent
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Note that the assembler allows to express the value for an immediate
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using any numerical literal whose two's complement encoding fits in
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the immediate field. For example, @code{-2}, @code{0xfffffffe} and
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@code{4294967294} all denote the same encoded 32-bit immediate, whose
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value may be then interpreted by different instructions as either as a
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negative or a positive number.
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@subsection Arithmetic instructions
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The destination register in these instructions act like an
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@ -1,3 +1,5 @@
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.*: Assembler messages:
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.*:2: Error: signed instruction operand out of range, shall fit in 32 bits
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.*:4: Error: signed instruction operand out of range, shall fit in 32 bits
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.*:1: Error: pc-relative offset out of range, shall fit in 16 bits
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.*:2: Error: pc-relative offset out of range, shall fit in 16 bits
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.*:3: Error: pc-relative offset out of range, shall fit in 16 bits
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.*:4: Error: pc-relative offset out of range, shall fit in 16 bits
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@ -1,4 +1,4 @@
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jeq %r1,%r2,2147483647
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jeq %r1,%r2,2147483647 ; Overflows.
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jlt %r3,%r4,2147483648 ; Overflows.
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jge %r5,10,-2147483648
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jge %r5,10,-2147483648 ; Overflows.
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ja -2147483649 ; Overflows.
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@ -1,3 +1,3 @@
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.*: Assembler messages:
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.*:2: Error: signed pc-relative offset out of range, shall fit in 16 bits
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.*:4: Error: signed pc-relative offset out of range, shall fit in 16 bits
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.*:2: Error: pc-relative offset out of range, shall fit in 16 bits
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.*:4: Error: pc-relative offset out of range, shall fit in 16 bits
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@ -1,4 +1,4 @@
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ja 32767
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jeq %r1,%r2,32768 ; Overflows
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jeq %r1,%r2,65536 ; Overflows
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jlt %r3,%r4,-32768
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jge %r5,10,-32769 ; Overflows
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@ -1,3 +1,3 @@
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.*: Assembler messages:
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.*:2: Error: signed pc-relative offset out of range, shall fit in 32 bits
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.*:4: Error: signed pc-relative offset out of range, shall fit in 32 bits
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.*:2: Error: pc-relative offset out of range, shall fit in 32 bits
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.*:4: Error: pc-relative offset out of range, shall fit in 32 bits
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@ -1,4 +1,4 @@
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call -2147483648
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call -2147483649 ; This overflows.
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call 2147483647
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call 2147483648 ; This overflows.
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call 4294967295
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call 4294967296 ; This overflows.
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@ -1,3 +1,3 @@
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.*: Assembler messages:
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.*:2: Error: signed immediate out of range, shall fit in 32 bits
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.*:4: Error: signed immediate out of range, shall fit in 32 bits
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.*:2: Error: immediate out of range, shall fit in 32 bits
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.*:4: Error: immediate out of range, shall fit in 32 bits
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@ -1,4 +1,4 @@
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add %r1, 2147483647
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or %r2, 2147483648 ; This overflows.
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xor %r3, -2147483648
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sub %r4, -2147483649 ; This overflows.
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or %r2, 4294967296 ; This overflows.
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xor %r3, 4294967295
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sub %r4, 4294967296 ; This overflows.
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@ -13,7 +13,5 @@ Disassembly of section .text:
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10: 05 00 ff fd 00 00 00 00 ja -3
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18: 05 00 00 00 00 00 00 00 ja 0
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18: R_BPF_GNU_64_16 undefined
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20: 06 00 00 00 ff ff 7f ff jal -32769
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28: 06 00 00 00 00 00 80 00 jal 32768
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30: 06 00 00 00 00 00 80 01 jal 32769
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38: 06 00 00 00 00 00 80 01 jal 32769
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20: 06 00 00 00 00 00 80 01 jal 32769
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28: 06 00 00 00 00 00 80 01 jal 32769
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@ -13,7 +13,5 @@ Disassembly of section .text:
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10: 05 00 fd ff 00 00 00 00 ja -3
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18: 05 00 00 00 00 00 00 00 ja 0
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18: R_BPF_GNU_64_16 undefined
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20: 06 00 00 00 ff 7f ff ff jal -32769
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28: 06 00 00 00 00 80 00 00 jal 32768
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30: 06 00 00 00 01 80 00 00 jal 32769
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38: 06 00 00 00 01 80 00 00 jal 32769
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20: 06 00 00 00 01 80 00 00 jal 32769
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28: 06 00 00 00 01 80 00 00 jal 32769
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@ -9,10 +9,6 @@
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;; The following instruction has an undefined symbol as a
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;; target. It is not to be relaxed.
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ja undefined + 10
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;; The following instructions are relaxed to JAL instructions
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;; so they can fit their displacements.
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ja -32769
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ja 32768
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;; The following instructions refer to a defined symbol that
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;; is not on reach. They shall be relaxed to a JAL.
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ja tail
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@ -11,15 +11,9 @@ Disassembly of section .text:
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0: 1d 12 80 00 00 00 00 00 jeq %r1,%r2,-32768
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8: ad 12 7f ff 00 00 00 00 jlt %r1,%r2,32767
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10: bd 12 ff fd 00 00 00 00 jle %r1,%r2,-3
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18: 3d 12 00 01 00 00 00 00 jge %r1,%r2,1
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18: 1d 12 00 01 00 00 00 00 jeq %r1,%r2,1
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20: 05 00 00 01 00 00 00 00 ja 1
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28: 06 00 00 00 ff ff 7f ff jal -32769
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28: 06 00 00 00 00 00 80 01 jal 32769
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30: 2d 12 00 01 00 00 00 00 jgt %r1,%r2,1
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38: 05 00 00 01 00 00 00 00 ja 1
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40: 06 00 00 00 00 00 80 00 jal 32768
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48: 1d 12 00 01 00 00 00 00 jeq %r1,%r2,1
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50: 05 00 00 01 00 00 00 00 ja 1
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58: 06 00 00 00 00 00 80 01 jal 32769
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60: 2d 12 00 01 00 00 00 00 jgt %r1,%r2,1
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68: 05 00 00 01 00 00 00 00 ja 1
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70: 06 00 00 00 00 00 80 01 jal 32769
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40: 06 00 00 00 00 00 80 01 jal 32769
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@ -11,15 +11,9 @@ Disassembly of section .text:
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0: 1d 21 00 80 00 00 00 00 jeq %r1,%r2,-32768
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8: ad 21 ff 7f 00 00 00 00 jlt %r1,%r2,32767
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10: bd 21 fd ff 00 00 00 00 jle %r1,%r2,-3
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18: 3d 21 01 00 00 00 00 00 jge %r1,%r2,1
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18: 1d 21 01 00 00 00 00 00 jeq %r1,%r2,1
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20: 05 00 01 00 00 00 00 00 ja 1
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28: 06 00 00 00 ff 7f ff ff jal -32769
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28: 06 00 00 00 01 80 00 00 jal 32769
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30: 2d 21 01 00 00 00 00 00 jgt %r1,%r2,1
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38: 05 00 01 00 00 00 00 00 ja 1
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40: 06 00 00 00 00 80 00 00 jal 32768
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48: 1d 21 01 00 00 00 00 00 jeq %r1,%r2,1
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50: 05 00 01 00 00 00 00 00 ja 1
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58: 06 00 00 00 01 80 00 00 jal 32769
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60: 2d 21 01 00 00 00 00 00 jgt %r1,%r2,1
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68: 05 00 01 00 00 00 00 00 ja 1
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70: 06 00 00 00 01 80 00 00 jal 32769
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40: 06 00 00 00 01 80 00 00 jal 32769
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@ -5,11 +5,6 @@
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;; The following instruction refers to a defined symbol that
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;; is on reach, so it should not be relaxed.
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jle %r1, %r2, 1b
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;; The following instructions are relaxed to sequences
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;; involving unconditional jumps, so they can fi their
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;; displacements.
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jge %r1, %r2, -32769
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jgt %r1, %r2, 32768
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;; The following instructions refer to a defined symbol that
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;; is not on reach. They shall be relaxed.
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jeq %r1, %r2, tail
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@ -1,3 +1,3 @@
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.*: Assembler messages:
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.*:2: Error: signed pc-relative offset out of range, shall fit in 16 bits
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.*:4: Error: signed pc-relative offset out of range, shall fit in 16 bits
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.*:2: Error: pc-relative offset out of range, shall fit in 16 bits
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.*:4: Error: pc-relative offset out of range, shall fit in 16 bits
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@ -1,4 +1,4 @@
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ldxh %r2, [%r1 + 32767]
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ldxw %r2, [%r1 + 32768] ; This overflows
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ldxh %r2, [%r1 + 65535]
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ldxw %r2, [%r1 + 65536] ; This overflows
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stxw [%r2 - 32768], %r1
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stxdw [%r2 - 32769], %r1 ; This overflows
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