[lld] r187645 - [PECOFF] A symbol with symbol with section number 0 and non-zero value represents a BSS atom.
Rui Ueyama
ruiu at google.com
Tue Aug 6 08:48:44 PDT 2013
On Tue, Aug 6, 2013 at 8:16 AM, Shankar Easwaran <shankare at codeaurora.org>wrote:
> On 8/5/2013 11:06 PM, Rui Ueyama wrote:
>
> On Mon, Aug 5, 2013 at 8:58 PM, Shankar Easwaran <shankare at codeaurora.org> <shankare at codeaurora.org>wrote:
>
>
> Isnt this supposed to be meant for common symbols ?
>
> I guess it's the correct terminology, but I don't know much about it. Is
> this different from atoms for BSS?
>
> This is the definition for ELF common symbols (extracted from Ian's blog)
> :-
>
> A section index of SHN_COMMON (0xfff2) indicates a common symbol. Common
> symbols were invented to handle Fortran common blocks, and they are also
> often used for uninitialized global variables in C. A common symbol has
> unusual semantics. Common symbols have a value of zero, but set the size
> field to the desired size. If one object file has a common symbol and
> another has a definition, the common symbol is treated as an undefined
> reference. If there is no definition for a common symbol, the program
> linker acts as though it saw a definition initialized to zero of the
> appropriate size. Two object files may have common symbols of different
> sizes, in which case the program linker will use the largest size. I
>
The MS COFF only says that such a symbol is a common symbol and does not
give any definition for that, but I'd think it refers to this definition.
I'll make a change accordingly. Thank you for the info!
> On 8/2/2013 12:25 AM, Rui Ueyama wrote:
>
>
> Author: ruiu
> Date: Fri Aug 2 00:25:31 2013
> New Revision: 187645
>
> URL: http://llvm.org/viewvc/llvm-**project?rev=187645&view=rev<http://llvm.org/viewvc/llvm-project?rev=187645&view=rev> <http://llvm.org/viewvc/llvm-project?rev=187645&view=rev>
> Log:
> [PECOFF] A symbol with symbol with section number 0 and non-zero value
> represents a BSS atom.
>
> Added:
> lld/trunk/test/pecoff/Inputs/**bss-undef.obj.yaml
> lld/trunk/test/pecoff/bss-**undef.test
> Modified:
> lld/trunk/lib/ReaderWriter/**PECOFF/ReaderCOFF.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/**PECOFF/ReaderCOFF.cpp
> URL: http://llvm.org/viewvc/llvm-**project/lld/trunk/lib/**
> ReaderWriter/PECOFF/**ReaderCOFF.cpp?rev=187645&r1=**
> 187644&r2=187645&view=diff<http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp?rev=187645&r1=187644&r2=187645&view=diff> <http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp?rev=187645&r1=187644&r2=187645&view=diff>
> ==============================**==============================**
> ==================
> --- lld/trunk/lib/ReaderWriter/**PECOFF/ReaderCOFF.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/**PECOFF/ReaderCOFF.cpp Fri Aug 2
> 00:25:31 2013
> @@ -161,6 +161,20 @@ private:
> // Filter non-defined atoms, and group defined atoms by its section.
> SectionToSymbolsT definedSymbols;
> for (const coff_symbol *sym : symbols) {
> + // A symbol with section number 0 and non-zero value represents an
> + // uninitialized data. I don't understand why there are two ways
> to define
> + // an uninitialized data symbol (.bss and this way), but that's
> how COFF
> + // works.
> + if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_**UNDEFINED &&
> + sym->Value > 0) {
> + StringRef name = _symbolName[sym];
> + uint32_t size = sym->Value;
> + auto *atom = new (_alloc) COFFBSSAtom(*this, name, sym, size, 0);
> + result.push_back(atom);
> + continue;
> + }
> +
> + // Skip if it's not for defined atom.
> if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_ABSOLUTE ||
> sym->SectionNumber == llvm::COFF::IMAGE_SYM_**UNDEFINED)
> continue;
>
> Added: lld/trunk/test/pecoff/Inputs/**bss-undef.obj.yaml
> URL: http://llvm.org/viewvc/llvm-**project/lld/trunk/test/pecoff/**
> Inputs/bss-undef.obj.yaml?rev=**187645&view=auto<http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml?rev=187645&view=auto> <http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml?rev=187645&view=auto>
> ==============================**==============================**
> ==================
> --- lld/trunk/test/pecoff/Inputs/**bss-undef.obj.yaml (added)
> +++ lld/trunk/test/pecoff/Inputs/**bss-undef.obj.yaml Fri Aug 2
> 00:25:31 2013
> @@ -0,0 +1,43 @@
> +---
> +header:
> + Machine: IMAGE_FILE_MACHINE_I386
> + Characteristics: [ ]
> +sections:
> + - Name: .text
> + Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE,
> IMAGE_SCN_MEM_READ ]
> + Alignment: 4
> + SectionData: ""
> + - Name: .data
> + Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_**DATA,
> IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
> + Alignment: 4
> + SectionData: 03000000
> +symbols:
> + - Name: .text
> + Value: 0
> + SectionNumber: 1
> + SimpleType: IMAGE_SYM_TYPE_NULL
> + ComplexType: IMAGE_SYM_DTYPE_NULL
> + StorageClass: IMAGE_SYM_CLASS_STATIC
> + NumberOfAuxSymbols: 1
> + AuxiliaryData: 000000000000000000000000000000**000000
> + - Name: .data
> + Value: 0
> + SectionNumber: 2
> + SimpleType: IMAGE_SYM_TYPE_NULL
> + ComplexType: IMAGE_SYM_DTYPE_NULL
> + StorageClass: IMAGE_SYM_CLASS_STATIC
> + NumberOfAuxSymbols: 1
> + AuxiliaryData: 040000000000000000000000000000**000000
> + - Name: _bssdata1
> + Value: 4
> + SectionNumber: 0
> + SimpleType: IMAGE_SYM_TYPE_NULL
> + ComplexType: IMAGE_SYM_DTYPE_NULL
> + StorageClass: IMAGE_SYM_CLASS_EXTERNAL
> + - Name: _bssdata2
> + Value: 4
> + SectionNumber: 0
> + SimpleType: IMAGE_SYM_TYPE_NULL
> + ComplexType: IMAGE_SYM_DTYPE_NULL
> + StorageClass: IMAGE_SYM_CLASS_EXTERNAL
> +...
>
> Added: lld/trunk/test/pecoff/bss-**undef.test
> URL: http://llvm.org/viewvc/llvm-**project/lld/trunk/test/pecoff/**
> bss-undef.test?rev=187645&**view=auto<http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/bss-undef.test?rev=187645&view=auto> <http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/bss-undef.test?rev=187645&view=auto>
> ==============================**==============================**
> ==================
> --- lld/trunk/test/pecoff/bss-**undef.test (added)
> +++ lld/trunk/test/pecoff/bss-**undef.test Fri Aug 2 00:25:31 2013
> @@ -0,0 +1,22 @@
> +# RUN: yaml2obj %p/Inputs/bss-undef.obj.yaml > %t.obj
> +#
> +# RUN: lld -flavor link /out:%t /subsystem:console /force -- %t.obj \
> +# RUN: && llvm-readobj -sections %t | FileCheck %s
> +
> +CHECK: Section {
> +CHECK: Number: 2
> +CHECK-NEXT: Name: .bss
> +CHECK-NEXT: VirtualSize: 0x0
> +CHECK-NEXT: VirtualAddress: 0x2000
> +CHECK-NEXT: RawDataSize: 512
> +CHECK-NEXT: PointerToRawData: 0x0
> +CHECK-NEXT: PointerToRelocations: 0x0
> +CHECK-NEXT: PointerToLineNumbers: 0x0
> +CHECK-NEXT: RelocationCount: 0
> +CHECK-NEXT: LineNumberCount: 0
> +CHECK-NEXT: Characteristics [
> +CHECK-NEXT: IMAGE_SCN_CNT_UNINITIALIZED_**DATA
> +CHECK-NEXT: IMAGE_SCN_MEM_READ
> +CHECK-NEXT: IMAGE_SCN_MEM_WRITE
> +CHECK-NEXT: ]
> +CHECK-NEXT: }
>
>
> ______________________________**_________________
> llvm-commits mailing listllvm-commits at cs.uiuc.eduhttp://lists.cs.uiuc.edu/**mailman/listinfo/llvm-commits<http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits> <http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits>
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
>
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130806/bcbd6d14/attachment.html>
More information about the llvm-commits
mailing list