Add "section" attribute

[4ntoine]

__attribute__ ((section("name")))

[4ntoine]

Assume regular 'section' attribute is for ARM. Otherwise should revert:

def Section : InheritableAttr, TargetSpecificAttr<TargetARM>

[4ntoine]

Tested:

source:

#include <avr/io.h>

 __attribute__ ((section (".CSEG")))
const int i = 31;

int main()
{
    DDRB = 0x00;        //configure portB as input
    DDRC = 0xFF;        //configure portC as output

    while(1)
    {
        PORTC = PINB;
    }
    return 0;
}

generated bitcode:

; ModuleID = '/tmp/avr/Test1.c'
target datalayout = "e-p:16:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8"
target triple = "avr"

@i = constant i16 31, section ".CSEG", align 2

; Function Attrs: nounwind
define i16 @main() #0 {
entry:
  %retval = alloca i16, align 2
  store i16 0, i16* %retval
  store volatile i8 0, i8* inttoptr (i16 36 to i8*), align 1
  store volatile i8 -1, i8* inttoptr (i16 39 to i8*), align 1
  br label %while.body

while.body:                                       ; preds = %entry, %while.body
  %0 = load volatile i8* inttoptr (i16 35 to i8*), align 1
  store volatile i8 %0, i8* inttoptr (i16 40 to i8*), align 1
  br label %while.body

return:                                           ; No predecessors!
  %1 = load i16* %retval
  ret i16 %1
}

attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.ident = !{!0}

!0 = metadata !{metadata !"clang version 3.6.0 (https://github.com/4ntoine/clang.git 2516492e3fe7fb4ed4aa25d733368035f6c17cde) (https://github.com/dylanmckay/llvm.git 1aea34ae240696b0c6f2903601a4a14da1244e1d)"}

seems to be ok

[dylanmckay]

Why is there a seperate section attribute for AVR? Can't we use the regular section attribute? It too adds the , section ".CSEG" qualifier to values, and the output seems to be the same.

[4ntoine]

They are almost identical.

Regular one:

def Section : InheritableAttr {
  let Spellings = [GCC<"section">, Declspec<"allocate">];
  let Args = [StringArgument<"Name">];
  let Subjects = SubjectList<[Function, GlobalVar,
                              ObjCMethod, ObjCProperty], ErrorDiag,
                             "ExpectedFunctionGlobalVarMethodOrProperty">;
  let Documentation = [SectionDocs];
}

AVR-specific:

def AVRSection : InheritableAttr, TargetSpecificAttr<TargetAVR> {
  let Spellings = [GNU<"section">];
  let Args = [StringArgument<"Name">];
  let Subjects = SubjectList<[Function, GlobalVar], ErrorDiag, "ExpectedFunctionGlobalVarMethodOrProperty">;
  let ParseKind = "Section";
  let Documentation = [SectionDocs];
}

I'm not sure about Declspec<"allocate"> and attribute usage in obj-c so it was removed. Probably should think about reverting. To be honest i've created new one and then found existing attribute with the same name

[dylanmckay]

Microsoft documents the allocate attribute as placing something in a specified section, so I believe the two attributes are semantically equivalent. Personally, I've never heard of it.

I'm not sure about Declspec<"allocate"> and attribute usage in obj-c so it was removed.

I'm not sure about obj-c either, but if we can use the regular Section attribute, which means touching less of clang's files and possibly supporting obj-c, it sounds like a good thing.

[dylanmckay]

Plus if we use the reguar Section, we don't have to handle it explicitly in AVR-LLVM and we can let the ELFObjectWriter class in LLVM handle it for us.

[4ntoine]

ok, agree. Reverted to use regular section attribute. But left TargetAVR declaration for future attributes