3rd Ping [PATCH v9 0/5] New attribute "counted_by" to annotate bounds for C99 FAM(PR108896)

[Qing Zhao <qing.zhao@oracle.com>]

Hi, 

This is the 3rd ping for the middle-end approval for this patch set. 
I’m hoping to commit this feature into GCC15 as early as possible to enable linux kernel to use it and have more testing. 

For your info, this new feature has been committed to CLANG since last October (https://github.com/llvm/llvm-project/pull/68750, https://github.com/llvm/llvm-project/pull/70606)

Linux kernel started to use the counted-by attribute in the source code since then with CLANG:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/compiler_attributes.h?h=v6.9#n97
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?h=v6.9&qt=grep&q=__counted_by

The patch set includes C FE changes, documentation changes, and middle end changes.

**All C FE changes + documentation changes have been approved by Joseph already (please see the approval below):
1/5 (All are C FE and documentation changes, approved):
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649857.html
2/5: (C FE approved)
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649189.html
4/5: (All are C FE changes, approved)
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649190.html
5/5: (C FE approved)
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649191.html

**All middle-end changes has been reviewed by Siddhesh, fixed all the comments raised by him, no remaining issue:
2/5: (middle-end reviewed without issue)
https://gcc.gnu.org/pipermail/gcc-patches/2024-March/647566.html
3/5: (All are Middle-end changes reviewed without issue)
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649256.html
5/5: (middle-end reviewed without issue)
https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649217.html

Okay for GCC15?

Thanks a lot !

Qing
> On May 7, 2024, at 10:14, Qing Zhao <qing.zhao@oracle.com> wrote:
> 
> 
> 
>> On May 7, 2024, at 10:02, Qing Zhao <qing.zhao@oracle.com> wrote:
>> 
>> 2nd Ping for the middle-end change approval. -:)
>> 
>> ******Approval status:
>> 
>> All C FE changes have been approved.
>> 
>> ******Review status:
>> 
>> All Middle-end changes have been reviewed by Sid, no remaining issue. 
>> 
>> Okay for GCC15? 
> 
> For convenience, the following is the links to the 9th version:
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649389.html
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649390.html
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649391.html
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649392.html
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649394.html
> https://gcc.gnu.org/pipermail/gcc-patches/2024-April/649393.html
> 
> One more note, CLANG has supported this attribute since last year.
> 
> Qing
>> 
>> 
>> 
>> thanks.
>> 
>> Qing
>> 
>>> Begin forwarded message:
>>> 
>>> From: Qing Zhao <qing.zhao@oracle.com>
>>> Subject: Re: [PATCH v9 0/5] New attribute "counted_by" to annotate bounds for C99 FAM(PR108896)
>>> Date: April 23, 2024 at 15:56:26 EDT
>>> To: Richard Biener <richard.guenther@gmail.com>, Siddhesh Poyarekar <siddhesh@gotplt.org>
>>> Cc: Joseph Myers <josmyers@redhat.com>, "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>, "isanbard@gmail.com" <isanbard@gmail.com>, Kees Cook <keescook@chromium.org>, "uecker@tugraz.at" <uecker@tugraz.at>
>>> 
>>> Ping for the middle-end change approval.
>>> 
>>> And an update on the status of the patch set:
>>> 
>>> ******Approval status:
>>> 
>>> All C FE changes have been approved.
>>> 
>>> ******Review status:
>>> 
>>> All Middle-end changes have been reviewed by Sid, no remaining issue. 
>>> 
>>> Okay for GCC15? 
>>> 
>>> thanks.
>>> 
>>> Qing
>>> 
>>>> On Apr 12, 2024, at 09:54, Qing Zhao <qing.zhao@oracle.com> wrote:
>>>> 
>>>> Hi,
>>>> 
>>>> This is the 9th version of the patch.
>>>> 
>>>> Compare with the 8th version, the difference are:
>>>> 
>>>> updates per Joseph's comments:
>>>> 
>>>> 1. in C FE, add checking for counted_by attribute for the new multiple definitions of the same tag for C23 in the routine "tagged_types_tu_compatible_p".
>>>>  Add a new testing case flex-array-counted-by-8.c for this. 
>>>>  This is for Patch 1;
>>>> 
>>>> 2. two minor typo fixes in c-typeck.cc. 
>>>>  This is for Patch 2;
>>>> 
>>>> Approval status:
>>>> 
>>>>  Patch 2's C FE change has been approved with minor typo fixes (the above 2);
>>>>  Patch 4 has been approved; 
>>>>  Patch 5's C FE change has been approved;
>>>> 
>>>> Review status:
>>>> 
>>>>  Patch 3, Patch 2 and Patch 5's Middle-end change have been review by Sid, No issue.
>>>> 
>>>> More review needed:
>>>> 
>>>>  Patch 1's new change to C FE (the above 1);
>>>>  Patch 2, 3 and 5's middle-end change need to be approved   
>>>> 
>>>> The 8th version is here:
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648559.html
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648560.html
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648561.html
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648562.html
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2024-March/648563.html
>>>> 
>>>> It based on the following original proposal:
>>>> 
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2023-November/635884.html
>>>> Represent the missing dependence for the "counted_by" attribute and its consumers
>>>> 
>>>> ******The summary of the proposal is:
>>>> 
>>>> * Add a new internal function ".ACCESS_WITH_SIZE" to carry the size information for every reference to a FAM field;
>>>> * In C FE, Replace every reference to a FAM field whose TYPE has the "counted_by" attribute with the new internal function ".ACCESS_WITH_SIZE";
>>>> * In every consumer of the size information, for example, BDOS or array bound sanitizer, query the size information or ACCESS_MODE information from the new internal function;
>>>> * When expansing to RTL, replace the internal function with the actual reference to the FAM field;
>>>> * Some adjustment to ipa alias analysis, and other SSA passes to mitigate the impact to the optimizer and code generation.
>>>> 
>>>> 
>>>> ******The new internal function
>>>> 
>>>> .ACCESS_WITH_SIZE (REF_TO_OBJ, REF_TO_SIZE, CLASS_OF_SIZE, TYPE_OF_SIZE, ACCESS_MODE, TYPE_OF_REF)
>>>> 
>>>> INTERNAL_FN (ACCESS_WITH_SIZE, ECF_LEAF | ECF_NOTHROW, NULL)
>>>> 
>>>> which returns the "REF_TO_OBJ" same as the 1st argument;
>>>> 
>>>> Both the return type and the type of the first argument of this function have been converted from the incomplete array type to the corresponding pointer type.
>>>> 
>>>> The call to .ACCESS_WITH_SIZE is wrapped with an INDIRECT_REF, whose type is the original imcomplete array type.
>>>> 
>>>> Please see the following link for why:
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2023-November/638793.html
>>>> https://gcc.gnu.org/pipermail/gcc-patches/2023-December/639605.html
>>>> 
>>>> 1st argument "REF_TO_OBJ": The reference to the object;
>>>> 2nd argument "REF_TO_SIZE": The reference to the size of the object,
>>>> 3rd argument "CLASS_OF_SIZE": The size referenced by the REF_TO_SIZE represents
>>>>  0: the number of bytes;
>>>>  1: the number of the elements of the object type;
>>>> 4th argument "TYPE_OF_SIZE": A constant 0 with the TYPE of the object
>>>> refed by REF_TO_SIZE
>>>> 5th argument "ACCESS_MODE":
>>>> -1: Unknown access semantics
>>>>  0: none
>>>>  1: read_only
>>>>  2: write_only
>>>>  3: read_write
>>>> 6th argument "TYPE_OF_REF": A constant 0 with the pointer TYPE to
>>>> to the original flexible array type.
>>>> 
>>>> ****** The Patch sets included:
>>>> 
>>>> 1. Provide counted_by attribute to flexible array member field;
>>>>     which includes:
>>>>     * "counted_by" attribute documentation;
>>>>     * C FE handling of the new attribute;
>>>>       syntax checking, error reporting;
>>>>     * testing cases;
>>>> 
>>>> 2. Convert "counted_by" attribute to/from .ACCESS_WITH_SIZE.
>>>>     which includes:
>>>>     * The definition of the new internal function .ACCESS_WITH_SIZE in internal-fn.def.
>>>>     * C FE converts every reference to a FAM with "counted_by" attribute to a call to the internal function .ACCESS_WITH_SIZE.
>>>>       (build_component_ref in c_typeck.cc)
>>>>       This includes the case when the object is statically allocated and initialized.
>>>>       In order to make this working, we should update initializer_constant_valid_p_1 and output_constant in varasm.cc to include calls to .ACCESS_WITH_SIZE.
>>>> 
>>>>       However, for the reference inside "offsetof", ignore the "counted_by" attribute since it's not useful at all. (c_parser_postfix_expression in c/c-parser.cc)
>>>> In addtion to "offsetof", for the reference inside operator "typeof" and
>>>> "alignof", we ignore counted_by attribute too.
>>>> When building ADDR_EXPR for the .ACCESS_WITH_SIZE in C FE,
>>>> replace the call with its first argument.
>>>> 
>>>>     * Convert every call to .ACCESS_WITH_SIZE to its first argument.
>>>>       (expand_ACCESS_WITH_SIZE in internal-fn.cc)
>>>>     * adjust alias analysis to exclude the new internal from clobbering anything.
>>>>       (ref_maybe_used_by_call_p_1 and call_may_clobber_ref_p_1 in tree-ssa-alias.cc)
>>>>     * adjust dead code elimination to eliminate the call to .ACCESS_WITH_SIZE when
>>>>       it's LHS is eliminated as dead code.
>>>>       (eliminate_unnecessary_stmts in tree-ssa-dce.cc)
>>>>     * Provide the utility routines to check the call is .ACCESS_WITH_SIZE and
>>>>       get the reference from the call to .ACCESS_WITH_SIZE.
>>>>       (is_access_with_size_p and get_ref_from_access_with_size in tree.cc)
>>>>     * testing cases. (for offsetof, static initialization, generation of calls to
>>>>       .ACCESS_WITH_SIZE, code runs correctly after calls to .ACCESS_WITH_SIZE are
>>>>       converted back)
>>>> 
>>>> 3. Use the .ACCESS_WITH_SIZE in builtin object size (sub-object only)
>>>>     which includes:
>>>>     * use the size info of the .ACCESS_WITH_SIZE for sub-object.
>>>>     * when the size is a negative integer, treat it as zero.
>>>>     * testing cases. 
>>>> 
>>>> 4 Use the .ACCESS_WITH_SIZE in bound sanitizer
>>>>     which includes:
>>>>     * Instrument array_ref with a call to .ACCESS_WITH_SIZE for bound sanitizer.
>>>>     * when the size is a negative integer, treat it as zero.
>>>>     * testing cases. 
>>>> 
>>>> 5. Add the 6th argument to .ACCESS_WITH_SIZE to carry the TYPE of the flexible array.
>>>>     which includes:
>>>>     * Add the 6th argument to .ACCESS_WITH_SIZE.
>>>>     * use the type of the 6th argument of the routine in tree-object-size.cc
>>>>     * testing case.
>>>> 
>>>> ******Remaining works: 
>>>> 
>>>> 6  Improve __bdos to use the counted_by info in whole-object size for the structure with FAM.
>>>> 7  Emit warnings when the user breaks the requirments for the new counted_by attribute
>>>>  compilation time: -Wcounted-by
>>>>  run time: -fsanitizer=counted-by
>>>>     * The initialization to the size field should be done before the first reference to the FAM field.
>>>>     * the array has at least # of elements specified by the size field all the time during the program.
>>>> 
>>>> I have bootstrapped and regression tested on both x86 and aarch64, no issue.
>>>> 
>>>> Let me know your comments.
>>>> 
>>>> thanks.
>>>> 
>>>> Qing