On 08/23/2018 03:27 AM, Bernd Edlinger wrote: > On 08/22/18 18:28, Martin Sebor wrote: >> On 08/22/2018 08:41 AM, Bernd Edlinger wrote: >>> Hi! >>> >>> >>> This patch adds some more checks to c_getstr to fix PR middle-end/87053 >>> wrong code bug. >>> >>> Unfortunately this patch alone is not sufficient to fix the problem, >>> but also the patch for PR 86714 that hardens c_getstr is necessary >>> to prevent the wrong folding. >>> >>> >>> Bootstrapped and reg-tested on top of my PR 86711/86714 patch. >>> Is it OK for trunk? >> >> This case is also the subject of the patch I submitted back in >> July for 86711/86714 and 86552. With it, GCC avoid folding >> the strlen call early and warns for the missing nul: >> >> warning: ‘__builtin_strlen’ argument missing terminating nul >> [-Wstringop-overflow=] >> if (__builtin_strlen (u.z) != 7) >> ^~~~~~~~~~~~~~~~ >> >> The patch doesn't doesn't prevent all such strings from being >> folded and it eventually lets fold_builtin_strlen() do its thing: >> >> /* To avoid warning multiple times about unterminated >> arrays only warn if its length has been determined >> and is being folded to a constant. */ >> if (nonstr) >> warn_string_no_nul (loc, NULL_TREE, fndecl, nonstr); >> >> return fold_convert_loc (loc, type, len); >> >> Handling this case is a matter of avoiding the folding here as >> well and moving the warning later. >> >> Since my patch is still in the review queue and does much more >> than just prevent folding of non-nul terminated arrays it should >> be reviewed first. >> > > Hmmm, now you made me curious. > > So I tried to install your patch (I did this on r263508 > since it does not apply to trunk, one thing I noted is > that part 4 and part 3 seem to create > gcc/testsuite/gcc.dg/warn-strcpy-no-nul.c > I did not check if they are identical or not). > > So I tried the test case from this PR on the compiler built with your patch: > > $ cat cat pr87053.c > /* PR middle-end/87053 */ > > const union > { struct { > char x[4]; > char y[4]; > }; > struct { > char z[8]; > }; > } u = {{"1234", "567"}}; > > int main () > { > if (__builtin_strlen (u.z) != 7) > __builtin_abort (); > } > $ gcc -S pr87053.c > pr87053.c: In function 'main': > pr87053.c:15:7: warning: '__builtin_strlen' argument missing terminating nul > [-Wstringop-overflow=] > 15 | if (__builtin_strlen (u.z) != 7) > | ^~~~~~~~~~~~~~~~ > pr87053.c:11:3: note: referenced argument declared here > 11 | } u = {{"1234", "567"}}; > | ^ > $ cat pr87053.s > .file "pr87053.c" > .text > .globl u > .section .rodata > .align 8 > .type u, @object > .size u, 8 > u: > .ascii "1234" > .string "567" > .text > .globl main > .type main, @function > main: > .LFB0: > .cfi_startproc > pushq %rbp > .cfi_def_cfa_offset 16 > .cfi_offset 6, -16 > movq %rsp, %rbp > .cfi_def_cfa_register 6 > call abort > .cfi_endproc > .LFE0: > .size main, .-main > .ident "GCC: (GNU) 9.0.0 20180813 (experimental)" > .section .note.GNU-stack,"",@progbits > > > So we get a warning, and still wrong code. > > That is the reason why I think this patch of yours adds > confusion by trying to fix everything in one step. > > And I would like you to think of ways how to solve > a problem step by step. > > And at this time, sorry, we should restore correctness issues. > And fix wrong-code issues. > If possible without breaking existing warnings, yes. > But no new warnings, sorry again. Just a note, Martin's most fix for 86711/86714 fixes codegen issues without breaking existing warnings or adding new warnings. The new warnings were broken out into follow-up patches.
jeff > Bernd. >