https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115496
Bug ID: 115496
Summary: RFE: new warning to detect suspicious multline string
literals
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: dmalcolm at gcc dot gnu.org
Target Milestone: ---
I find I often forget to add trailing newlines when composing multiline string
literals in C/C++.
For example:
const char *str
= ("this is the first line\n"
"this is the second line"
"this is the third line\n");
where the supposed "second line" is missing a trailing "\n" and thus the string
is actually:
this is the first line
this is the second linethis is the third line
For a more insidious example, consider:
https://fobes.dev/general/2024/02/29/inline-assembly-dangers.html
where the code had this string literal:
asm volatile(
"# Clear bss area"
"la $2, _fbss"
"la $3, _end"
"1:"
"sltu $1, $2, $3"
"beq $1, $0, 2f"
"nop"
"sq $0, ($2)"
"addiu $2, $2, 16"
"j 1b"
"nop"
"2:"
" \n"
"# Save first argument \n"
"la $2, %0 \n"
"sw $4, ($2) \n"
" \n"
"# SetupThread \n"
"la $4, _gp \n"
"la $5, _stack \n"
"la $6, _stack_size \n"
"la $7, %1 \n"
"la $8, ExitThread \n"
"move $gp, $4 \n"
"addiu $3, $0, 60 \n"
"syscall \n"
"move $sp, $2 \n"
" \n"
"# Jump to _main \n"
"j %2 \n"
: /* No outputs. */
: "R"(args_start), "R"(args), "Csy"(_main));
Note that some lines have trailing "\n", but others don't, so that this is
actually:
"# Clear bss areala $2, _fbssla $3, _end1:sltu $1, $2, $3beq
$1, $0, 2fnopsq $0, ($2)[...snip...]"
" \n"
"# Save first argument \n"
"la $2, %0 \n"
"sw $4, ($2) \n"
" \n"
[...snip...]
and thus the "comment to end of line" in the assembler was treating much more
that one might expect from a casual reading of the C source.
Proposal: a new warning that detects suspicious line continuations in multiline
strings. I'm not sure precisely what the heuristics should be, but something
like:
- the string literal is on multiple source lines
- at least some of the lines have terminating "\n" characters
- some of the lines don't have terminating "\n" characters (warn for these) -
but probably don't worry about the final line
- probably some other heuristics
Perhaps: "-Wsuspicious-multiline-string-literal" or somesuch?
