[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 Andrew Pinski changed: What|Removed |Added Severity|normal |enhancement
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 --- Comment #12 from jwjagersma at gmail dot com --- (In reply to Xi Ruoyao from comment #11) > Generally a patch should be sent to gcc-patc...@gcc.gnu.org. See > https://gcc.gnu.org/contribute.html. The patches attached to a Bugzilla > ticket are considered prototypes and for discussion only. This patch isn't complete yet, I posted it here in hopes of receiving some comments. It works for simple structs that are managed externally (eg, from inline asm). But other than that it doesn't integrate with the C++ type system so well. There is no way to make AS-qualified ctors/dtors (in fact, calling a dtor on an AS-qualified ptr/ref is currently allowed - that's very bad), and also no placement-new for AS-qualified pointers. Granted, I don't think clang implements that either, but it does provide stuff like __builtin_memcpy(). That is missing from this patch. I also recall running into one bug where it generated code to access a stack variable via fs:[esp]. I think it was something to do with rvalue references? But it disappeared when I attempted to write a smaller test case, couldn't figure that one out.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 Xi Ruoyao changed: What|Removed |Added CC||xry111 at gcc dot gnu.org Keywords||patch --- Comment #11 from Xi Ruoyao --- Generally a patch should be sent to gcc-patc...@gcc.gnu.org. See https://gcc.gnu.org/contribute.html. The patches attached to a Bugzilla ticket are considered prototypes and for discussion only.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 Adam Belay changed: What|Removed |Added CC||abelay at mit dot edu --- Comment #10 from Adam Belay --- I realize this bug and patch is a couple years old, but I wanted to mention that my research group is working on a new kernel in C++ and this feature would be very useful to us. Without it, the FS and GS segment can only be accessed via inline assembly, which is less convenient and more difficult for GCC to optimize.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 --- Comment #9 from jwjagersma at gmail dot com --- Created attachment 51840 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51840=edit diagnostics This patch adds checks for: - Top-level AS-qualifiers on fields, local variables, function parameters and function return types. - Assignment of pointers and references to different address spaces. - Combining AS-qualifiers in template substitution. An appropriate error message is emitted in each case. Not detected: AS-qualifiers on non-type template parameters (but they are stripped and ignored, of course). I think this covers most invalid uses. Am I missing anything?
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 --- Comment #8 from jwjagersma at gmail dot com --- Created attachment 51808 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51808=edit basic implementation Tentative patch. Produces working code but could use some (many) checks to diagnose incorrect usage, eg. AS-qualified struct fields, function parameters, non-type template parameters. Assigning an AS-qualified pointer to non-qualified is already diagnosed correctly, but the inverse is not. I don't know if mangling address-space-qualified member functions would be covered by ABI version 10, or if the version number needs to be bumped.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549
--- Comment #7 from Thiago Macieira ---
(In reply to Andrew Pinski from comment #6)
> The above is not the reason why namespaces are not handled in GCC's C++
> front-end. The reason why they are not handled in C++ is because you need
> to handle them in overloads and templates correctly. Does clang handle
> those correctly or does it ignore that issue?
It handles them:
$ clang -O2 -S -o - -include stdint.h -xc++ - <<<'template void
f(T); void f() { auto tib = (void * __seg_fs*)(0); f(tib); }' | c++filt
.text
.file "-"
.globl f() # -- Begin function f()
.p2align4, 0x90
.type f(),@function
f(): # @f()
.cfi_startproc
# %bb.0:
xorl%edi, %edi
jmp void f(void* AS257*) # TAILCALL
The mangled symbol was _Z1fIPU5AS257PvEvT_. That "AS257" is encoded as U5AS257,
which is an extended qualifier.
:
5.1.5.1 Qualified types
::=
::= *
::= U [] # vendor extended
type qualifier
::= [r] [V] [K]# restrict (C99), volatile, const
::= R # & ref-qualifier
::= O # && ref-qualifier
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549
--- Comment #6 from Andrew Pinski ---
(In reply to Thiago Macieira from comment #5)
> BTW, Clang solved this by making __seg_fs, __seg_gs macros that resolve to
> __attribute__:
> That way, they don't need to be deduced as qualifiers in C, like const,
> volatile and _Atomic.
You still need to handle the attribute like qualifiers
> So this compiles with Clang in C++:
>
> void *tid() { auto tib = (void * __seg_fs*)(0); return *tid; }
The above is not the reason why namespaces are not handled in GCC's C++
front-end. The reason why they are not handled in C++ is because you need to
handle them in overloads and templates correctly. Does clang handle those
correctly or does it ignore that issue?
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549
--- Comment #5 from Thiago Macieira ---
BTW, Clang solved this by making __seg_fs, __seg_gs macros that resolve to
__attribute__:
$ clang -dM -E -xc /dev/null | grep __seg_.s
#define __seg_fs __attribute__((address_space(257)))
#define __seg_gs __attribute__((address_space(256)))
That way, they don't need to be deduced as qualifiers in C, like const,
volatile and _Atomic.
So this compiles with Clang in C++:
void *tid() { auto tib = (void * __seg_fs*)(0); return *tid; }
_Z3tibv:# @_Z3tibv
movq%fs:0, %rax
retq
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 --- Comment #4 from Thiago Macieira --- And in GCC 11. gcc version 11.0.1 20210308 (experimental) (GCC)
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 Julian Stecklina changed: What|Removed |Added CC||js at alien8 dot de --- Comment #3 from Julian Stecklina --- This is still an issue with 8.3.1.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2017-03-27 Ever confirmed|0 |1 --- Comment #2 from Jonathan Wakely --- (In reply to Thiago Macieira from comment #0) > It works in C: > > $ cat test.c > __seg_gs char * ptr; > $ gcc -c test.c && echo Success > Success It's documenbted as being a feature in GNU C, and it doesn't say it's also supported for C++. > But not in C++: > > $ gcc -xc++ -c test.c > test.c:1:1: error: ‘__seg_gs’ does not name a type > > Even though it's advertised as supported: > > $ gcc -xc++ -dM -E /dev/null | grep SEG_GS > #define __SEG_GS 1 That seems persuasive. Either the macro shouldn't be defined or it should be supported.
[Bug c++/69549] Named Address Spaces does not compile in C++
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69549 --- Comment #1 from Thiago Macieira --- Bump? Still happening on 7.0 (built 20160502)
