bpf: avoid creating wrong symbols while parsing

To support the "pseudo-C" asm dialect in BPF, the BPF parser must often
attempt multiple different templates for a single instruction. In some
cases this can cause the parser to incorrectly parse part of the
instruction opcode as an expression, which leads to the creation of a
new undefined symbol.

Once the parser recognizes the error, the expression is discarded and it
tries again with a new instruction template. However, symbols created
during the process are added to the symbol table and are not removed
even if the expression is discarded.

This is a problem for BPF: generally the assembled object will be loaded
directly to the Linux kernel, without being linked. These erroneous
parser-created symbols are rejected by the kernel BPF loader, and the
entire object is refused.

This patch remedies the issue by tentatively creating symbols while
parsing instruction operands, and storing them in a temporary list
rather than immediately inserting them into the symbol table. Later,
after the parser is sure that it has correctly parsed the instruction,
those symbols are committed to the real symbol table.

This approach is modeled directly after Jan Beulich's patch for RISC-V:

  commit 7a29ee290307087e1749ce610207e93a15d0b78d
  RISC-V: adjust logic to avoid register name symbols

Many thanks to Jan for recognizing the problem as similar, and pointing
me to that patch.

gas/

	* config/tc-bpf.c (parsing_insn_operands): New.
	(parse_expression): Set it here.
	(deferred_sym_rootP, deferred_sym_lastP): New.
	(orphan_sym_rootP, orphan_sym_lastP): New.
	(bpf_parse_name): New.
	(parse_error): Clear deferred symbol list on error.
	(md_assemble): Clear parsing_insn_operands. Commit deferred
	symbols to symbol table on successful parse.
	* config/tc-bpf.h (md_parse_name): Define to...
	(bpf_parse_name): ...this. New prototype.
	* testsuite/gas/bpf/asm-extra-sym-1.s: New test source.
	* testsuite/gas/bpf/asm-extra-sym-1.d: New test.
	* testsuite/gas/bpf/bpf.exp: Run new test.

0 files changed, 0 insertions, 0 deletions