Hi, this completes the previous patches, and adds a check in varasm.c that ensures that all string constants are NUL terminated, And that varasm does not strip anything but _exactly_ one NUL character.
Bootstrapped and reg-tested on x86_64-pc-linux-gnu. Is it OK for trunk? Thanks Bernd.
2018-08-01 Bernd Edlinger <bernd.edlin...@hotmail.de> * varasm.c (check_string_literal): New checking function. (output_constant): Use it. diff -pur gcc/varasm.c gcc/varasm.c --- gcc/varasm.c 2018-07-17 11:19:27.000000000 +0200 +++ gcc/varasm.c 2018-07-31 10:16:12.058827505 +0200 @@ -4774,6 +4774,29 @@ initializer_constant_valid_for_bitfield_ return false; } +/* Check if a STRING_CST fits into the field. + Tolerate only the case when the NUL termination + does not fit into the field. */ + +bool +check_string_literal (tree string, unsigned HOST_WIDE_INT size) +{ + tree eltype = TREE_TYPE (TREE_TYPE (string)); + unsigned HOST_WIDE_INT elts = tree_to_uhwi (TYPE_SIZE_UNIT (eltype)); + const char *p = TREE_STRING_POINTER (string); + int len = TREE_STRING_LENGTH (string); + + if (elts != 1 && elts != 2 && elts != 4) + return false; + if (len <= 0 || len % elts != 0) + return false; + if ((unsigned)len != size && (unsigned)len != size + elts) + return false; + if (memcmp (p + len - elts, "\0\0\0\0", elts) != 0) + return false; + return true; +} + /* output_constructor outer state of relevance in recursive calls, typically for nested aggregate bitfields. */ @@ -4942,6 +4965,7 @@ output_constant (tree exp, unsigned HOST case STRING_CST: thissize = MIN ((unsigned HOST_WIDE_INT)TREE_STRING_LENGTH (exp), size); + gcc_checking_assert (check_string_literal (exp, thissize)); assemble_string (TREE_STRING_POINTER (exp), thissize); break; case VECTOR_CST: