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[ELF][ARM] Implement support for Tag_ABI_VFP_args 

The Tag_ABI_VFP_args build attribute controls the procedure call standard
used for floating point parameters on ARM. The values are:
0 - Base AAPCS (FP Parameters passed in Core (Integer) registers
1 - VFP AAPCS (FP Parameters passed in FP registers)
2 - Toolchain specific (Neither Base or VFP)
3 - Compatible with all (No use of floating point parameters)

If the Tag_ABI_VFP_args build attribute is missing it has an implicit value
of 0.
    
We use the attribute in two ways:
- Detect a clash in calling convention between Base, VFP and Toolchain.
we follow ld.bfd's lead and do not error if there is a clash between an
implicit Base AAPCS caused by a missing attribute. Many projects
including the hard-float (VFP AAPCS) version of glibc contain assembler
files that do not use floating point but do not have Tag_ABI_VFP_args.
- Set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD ELF header flag
for Base or VFP AAPCS respectively. This flag is used by some ELF
loaders.
    
References:
- Addenda to, and Errata in, the ABI for the ARM Architecture for
Tag_ABI_VFP_args
- Elf for the ARM Architecture for ELF header flags
    
Fixes PR36009
    
Differential Revision: https://reviews.llvm.org/D49993

llvm-svn: 338377
This commit is contained in:
Peter Smith 2018-07-31 13:41:59 +00:00
parent 4aec86d37a
commit 70997f9a4e
11 changed files with 241 additions and 1 deletions
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11
lld/ELF/Arch/ARM.cpp
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@ -97,10 +97,19 @@ ARM::ARM() {
}
uint32_t ARM::calcEFlags() const {
// The ABIFloatType is used by loaders to detect the floating point calling
// convention.
uint32_t ABIFloatType = 0;
if (Config->ARMVFPArgs == ARMVFPArgKind::Base ||
Config->ARMVFPArgs == ARMVFPArgKind::Default)
ABIFloatType = EF_ARM_ABI_FLOAT_SOFT;
else if (Config->ARMVFPArgs == ARMVFPArgKind::VFP)
ABIFloatType = EF_ARM_ABI_FLOAT_HARD;
// We don't currently use any features incompatible with EF_ARM_EABI_VER5,
// but we don't have any firm guarantees of conformance. Linux AArch64
// kernels (as of 2016) require an EABI version to be set.
return EF_ARM_EABI_VER5;
return EF_ARM_EABI_VER5 | ABIFloatType;
}
RelExpr ARM::getRelExpr(RelType Type, const Symbol &S,

4
lld/ELF/Config.h
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@ -58,6 +58,9 @@ enum class SortSectionPolicy { Default, None, Alignment, Name, Priority };
// For --target2
enum class Target2Policy { Abs, Rel, GotRel };
// For tracking ARM Float Argument PCS
enum class ARMVFPArgKind { Default, Base, VFP, ToolChain };
struct SymbolVersion {
llvm::StringRef Name;
bool IsExternCpp;
@ -196,6 +199,7 @@ struct Configuration {
StripPolicy Strip;
UnresolvedPolicy UnresolvedSymbols;
Target2Policy Target2;
ARMVFPArgKind ARMVFPArgs = ARMVFPArgKind::Default;
BuildIdKind BuildId = BuildIdKind::None;
ELFKind EKind = ELFNoneKind;
uint16_t DefaultSymbolVersion = llvm::ELF::VER_NDX_GLOBAL;

42
lld/ELF/InputFiles.cpp
View File

@ -494,6 +494,46 @@ void ObjFile<ELFT>::initializeSections(
}
}
// For ARM only, to set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD
// flag in the ELF Header we need to look at Tag_ABI_VFP_args to find out how
// the input objects have been compiled.
static void updateARMVFPArgs(const ARMAttributeParser &Attributes,
const InputFile *F) {
if (!Attributes.hasAttribute(ARMBuildAttrs::ABI_VFP_args))
// If an ABI tag isn't present then it is implicitly given the value of 0
// which maps to ARMBuildAttrs::BaseAAPCS. However many assembler files,
// including some in glibc that don't use FP args (and should have value 3)
// don't have the attribute so we do not consider an implicit value of 0
// as a clash.
return;
unsigned VFPArgs = Attributes.getAttributeValue(ARMBuildAttrs::ABI_VFP_args);
ARMVFPArgKind Arg;
switch (VFPArgs) {
case ARMBuildAttrs::BaseAAPCS:
Arg = ARMVFPArgKind::Base;
break;
case ARMBuildAttrs::HardFPAAPCS:
Arg = ARMVFPArgKind::VFP;
break;
case ARMBuildAttrs::ToolChainFPPCS:
// Tool chain specific convention that conforms to neither AAPCS variant.
Arg = ARMVFPArgKind::ToolChain;
break;
case ARMBuildAttrs::CompatibleFPAAPCS:
// Object compatible with all conventions.
return;
default:
error(toString(F) + ": unknown Tag_ABI_VFP_args value: " + Twine(VFPArgs));
return;
}
// Follow ld.bfd and error if there is a mix of calling conventions.
if (Config->ARMVFPArgs != Arg && Config->ARMVFPArgs != ARMVFPArgKind::Default)
error(toString(F) + ": incompatible Tag_ABI_VFP_args");
else
Config->ARMVFPArgs = Arg;
}
// The ARM support in lld makes some use of instructions that are not available
// on all ARM architectures. Namely:
// - Use of BLX instruction for interworking between ARM and Thumb state.
@ -573,6 +613,8 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
ArrayRef<uint8_t> Contents = check(this->getObj().getSectionContents(&Sec));
Attributes.Parse(Contents, /*isLittle*/ Config->EKind == ELF32LEKind);
updateSupportedARMFeatures(Attributes);
updateARMVFPArgs(Attributes, this);
// FIXME: Retain the first attribute section we see. The eglibc ARM
// dynamic loaders require the presence of an attribute section for dlopen
// to work. In a full implementation we would merge all attribute sections.

16
lld/test/ELF/Inputs/arm-vfp-arg-base.s Normal file
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@ -0,0 +1,16 @@
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 0 // Tag_ABI_VFP_args = 0 (AAPCS, Base variant)
.syntax unified
.global f0
.type f0, %function
f0: bx lr

16
lld/test/ELF/Inputs/arm-vfp-arg-compat.s Normal file
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@ -0,0 +1,16 @@
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 3 // Tag_ABI_VFP_args = 3 (Compatible with all)
.syntax unified
.global f3
.type f3, %function
f3: bx lr

15
lld/test/ELF/Inputs/arm-vfp-arg-toolchain.s Normal file
View File

@ -0,0 +1,15 @@
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 2 // Tag_ABI_VFP_args = 2 (Toolchain specific)
.syntax unified
.global f2
.type f1, %function
f2: bx lr

15
lld/test/ELF/Inputs/arm-vfp-arg-vfp.s Normal file
View File

@ -0,0 +1,15 @@
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 1 // Tag_ABI_VFP_args = 1 (AAPCS, VFP variant)
.syntax unified
.global f1
.type f1, %function
f1: bx lr

1
lld/test/ELF/arm-eabi-version.s
View File

@ -9,6 +9,7 @@ _start:
bx lr
// CHECK: Flags [
// CHECK-NEXT: 0x200
// CHECK-NEXT: 0x1000000
// CHECK-NEXT: 0x4000000
// CHECK-NEXT: ]

29
lld/test/ELF/arm-tag-vfp-args-errs.s Normal file
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@ -0,0 +1,29 @@
// REQUIRES:arm
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-base.s -o %tbase.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-vfp.s -o %tvfp.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-toolchain.s -o %ttoolchain.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
// RUN: not ld.lld %t.o %tbase.o %tvfp.o 2>&1 | FileCheck %s
// RUN: not ld.lld %t.o %tbase.o %ttoolchain.o 2>&1 | FileCheck %s
// RUN: not ld.lld %t.o %tvfp.o %tbase.o 2>&1 | FileCheck %s
// RUN: not ld.lld %t.o %tvfp.o %ttoolchain.o 2>&1 | FileCheck %s
// RUN: not ld.lld %t.o %ttoolchain.o %tbase.o 2>&1 | FileCheck %s
// RUN: not ld.lld %t.o %ttoolchain.o %tvfp.o 2>&1 | FileCheck %s
// CHECK: incompatible Tag_ABI_VFP_args
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 3 // Tag_ABI_VFP_args = 3 (Compatible with all)
.syntax unified
.globl _start
.type _start, %function
_start: bx lr

21
lld/test/ELF/arm-tag-vfp-args-illegal.s Normal file
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@ -0,0 +1,21 @@
// REQUIRES:arm
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
// RUN: not ld.lld %t.o -o %t 2>&1 | FileCheck %s
// CHECK: arm-tag-vfp-args-illegal.s.tmp.o: unknown Tag_ABI_VFP_args value: 5
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
.eabi_attribute 28, 5 // Tag_ABI_VFP_args = 5 (Illegal value)
.syntax unified
.globl _start
.type _start, %function
_start: bx lr

72
lld/test/ELF/arm-tag-vfp-args.s Normal file
View File

@ -0,0 +1,72 @@
// REQUIRES:arm
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-base.s -o %tbase.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-vfp.s -o %tvfp.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-toolchain.s -o %ttoolchain.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %S/Inputs/arm-vfp-arg-compat.s -o %tcompat.o
// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
// The default for this file is 0 (Base AAPCS)
// RUN: ld.lld %t.o -o %tdefault
// RUN: llvm-readobj -file-headers %tdefault | FileCheck -check-prefix=CHECK-BASE %s
// Expect explicit Base AAPCS.
// RUN: ld.lld %t.o %tbase.o -o %tbase
// RUN: llvm-readobj -file-headers %tbase | FileCheck -check-prefix=CHECK-BASE %s
// Expect explicit Base AAPCS when linking Base and Compatible.
// RUN: ld.lld %t.o %tbase.o %tcompat.o -o %tbasecompat
// RUN: llvm-readobj -file-headers %tbasecompat | FileCheck -check-prefix=CHECK-BASE %s
// CHECK-BASE: Flags [ (0x5000200)
// CHECK-BASE-NEXT: 0x200
// CHECK-BASE-NEXT: 0x1000000
// CHECK-BASE-NEXT: 0x4000000
// CHECK-BASE-NEXT: ]
// Expect Hard float VFP AAPCS
// RUN: ld.lld %t.o %tvfp.o -o %tvfp
// RUN: llvm-readobj -file-headers %tvfp | FileCheck -check-prefix=CHECK-VFP %s
// Expect Hard float VFP AAPCS when linking VFP and Compatible
// RUN: ld.lld %t.o %tvfp.o %tcompat.o -o %tvfpcompat
// RUN: llvm-readobj -file-headers %tvfpcompat | FileCheck -check-prefix=CHECK-VFP %s
// CHECK-VFP: Flags [ (0x5000400)
// CHECK-VFP-NEXT: 0x400
// CHECK-VFP-NEXT: 0x1000000
// CHECK-VFP-NEXT: 0x4000000
// CHECK-VFP-NEXT: ]
// Expect Toolchain specifc to not use either Base or VFP AAPCS
// RUN: ld.lld %t.o %ttoolchain.o -o %ttoolchain
// RUN: llvm-readobj -file-headers %ttoolchain | FileCheck -check-prefix=CHECK-TOOLCHAIN %s
// Expect Toolchain and Compatible to have same affect as Toolchain.
// RUN: ld.lld %t.o %ttoolchain.o %tcompat.o -o %ttoolchaincompat
// RUN: llvm-readobj -file-headers %ttoolchaincompat | FileCheck -check-prefix=CHECK-TOOLCHAIN %s
// CHECK-TOOLCHAIN: Flags [ (0x5000000)
// CHECK-TOOLCHAIN-NEXT: 0x1000000
// CHECK-TOOLCHAIN-NEXT: 0x4000000
// CHECK-TOOLCHAIN-NEXT: ]
.arch armv7-a
.eabi_attribute 20, 1
.eabi_attribute 21, 1
.eabi_attribute 23, 3
.eabi_attribute 24, 1
.eabi_attribute 25, 1
.eabi_attribute 26, 2
.eabi_attribute 30, 6
.eabi_attribute 34, 1
.eabi_attribute 18, 4
// We do not specify Tag_ABI_VFP_args (.eabi_attribute 28) in this file.
// When omitted the value of the tag defaults to 0, however if there
// are other files with explicit Tag_ABI_VFP_args we use that in
// preference.
.syntax unified
.globl _start
.type _start, %function
_start: bx lr