eddyz87 added a comment.
Hi @dblaikie,
After this revision landed yesterday one BPF kernel selftest (written in C)
stopped building. I narrowed the issue to the following example:
#define SEC(n) __attribute__((section(n)))
const int with_init SEC("foo") = 1;
const int no_init SEC("foo");
It fails with the following error:
$ clang -c t.c -o -
t.c:4:11: error: 'no_init' causes a section type conflict with 'with_init'
4 | const int no_init SEC("foo");
| ^
t.c:3:11: note: declared here
3 | const int with_init SEC("foo") = 1;
| ^
1 error generated.
The error occurs because clang infers `PSF_Read` attribute for section "foo"
when `with_init` is processed and `PSF_Read | PSF_Write` attributes for section
"foo" when `no_init` is processed, thus reporting `diag::err_section_conflict`.
The behavior changed because of the following lines introduced in this revision:
void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
...
if (GlobalStorage && var->isThisDeclarationADefinition() &&
!inTemplateInstantiation()) {
...
if (var->hasInit() && HasConstInit && !(Reason =
var->getType().isNonConstantStorage(Context, true, false))) {
Stack = &ConstSegStack;
} else {
SectionFlags |= ASTContext::PSF_Write;
Stack = var->hasInit() && HasConstInit ? &DataSegStack : &BSSSegStack;
}
...
}
...
}
Because of the `var->hasInit()` check any global w/o initializer gets a
`PSF_Write` flag, which was not the case before this revision. So, now if one
wants to have some `const` globals in the same section, these globals need to
have an initializer.
I checked C language standard (N3088, section "6.7.3 Type qualifiers") and it
does not offer much to tell if my example is correct or not, so I guess it is
implementation dependent. GCC accepts my example w/o errors or warnings.
So, a question: might it be the case that `var->hasInit()` check is too
restrictive?
(I do understand that w/o some custom linker behavior `const` globals w/o
initializer don't make much sense).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D156726/new/
https://reviews.llvm.org/D156726
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